AAPM Spring Clinical Meeting – Abstracts

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Fetus Phantom Constructions for Organ Dose Assessment of Pregnant Patients Who Underwent Radiotherapy

R Makkia^1,*, K Nelson², M Dingfelder³

(1) East Carolina University, Greenville, NC, (2) Vidant Medical Center, Greeville, NC, (3) East Carolina University, Greenville, NC

Purpose

To accurately estimate the radiation dose to the fetus and assess the uncertainty of fetus position and rotation for a pregnant patient who is undergoing radiation therapy or diagnostic treatment using a series of realistic fetus computational model sets.

Methods

Three computational phantom models were obtained using de‐identified good quality MRI and CT imaging data for each fetus model as a starting point to construct a complete anatomically accurate fetus, gravid uterus, and placenta. All Radiological images in DICOM sets were obtained from Vidant Medical Center archive to conduct this study. The method started with outlines most of the fetus organs from radiological images via Velocity TPS and exported in the DICOM‐STRUCTURE set, which then was imported to Rhinoceros software, 3D model software for further reconstruction. All fetus volume organs were adjusting to match ICRP‐89 data record. Since radiotherapy is not allowed during the first trimester of pregnancy, our fetus model series ages start from 20, 31, and 35 weeks of pregnancy. After the models were finished, different fetus angles and locations were applied to represent fetus motion inside the uterus for each trimester of pregnancy with the guide of ultra sound images. Researchers have created a couple of computational fetus phantoms, but most of them have either been scaled to match certain weeks or lack of representing realistic models. However, no research has been done to show how the fetus angle and location may lead to uncertainty in dose calculations.

Results

A series of computational fetus models can be used to estimate the radiation dose to the fetus and evaluate the risk from radiation exposure due to a particular procedure.

Conclusion

This approach is demonstrating that newly developed fetus phantom models provide realistic anatomical details that are useful in treatment planning and ultimately risk assessment for pregnant patient.

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How to Determine the MRI Safety and Compatibility of an Implant or a Medical Device?

S Sammet^*

(1) University of Chicago, Chicago, IL

Purpose

To give an overview on how to determine the MRI safety and compatibility of an implant or a medical device.

Methods

An introduction to MRI safety including published books and searchable on‐line catalogs that list MRI‐safe devices and MRI‐safe implants with their allowed magnetic field strengths and gradient limitations will be provided. A detailed decision matrix with a step‐by step analysis on how to determine the MR safety of implants which are not listed in the literature or in online resources will be introduced. Works on MRI safety, published books and searchable on‐line catalogs that list MRI‐safe devices and MRI‐safe implants with their allowed magnetic field strengths and gradient limitations will be listed. This includes an introduction of the Food and Drug Administration labeling of devices and how to determine manufacturer and model of any implanted devices. Examples will demonstrate how to locate the MRI safety information in the manufacturer's labeling. A decision matrix on how to determine the MR safety will be provided for implants which are not listed in the literature or in on‐line resources. This decision matrix includes a step‐by‐step analysis to determine the MR safety. Responsibilities of MR Safety Officers and MR Medical Directors in the decision process will be discussed. For MR conditional devices, examples of scan conditions such as static magnetic field strength, coil types, specific absorption rate, maximum spatial field gradient, and dB/dt limitations will be demonstrated.

Results

A detailed MRI safety screening of implants and devices can prevent injuries. The introduced practical screening guideline improves the safety of patients with implants and medical devices.

Conclusion

Regular MRI safety training for staff, comprehensive screening forms and thorough patient evaluations, patient interviews before the exam, proper patient positioning, and constant visual and audio monitoring during the exam will improve the safety of patients.

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Electronic Records with Alerts for CT Technologist QC Across Multiple Locations

K Little^*, A Leighty, X Jiang, X Yang, D Hintenlang

(1) Ohio State University, Columbus, OH

Purpose

To simplify the recording and review of technologists’ quality control (QC) in computed tomography (CT) across multiple locations, to enable email‐based alerts for missed QC, and to immediately identify out‐of‐range QC results using software available at our institution.

Methods

Daily, weekly, and monthly QC forms for the diagnostic CT scanners in our system were implemented with Microsoft Excel and hosted using our institution's existing Microsoft SharePoint website. The QC site could be accessed by technologists, administrators, and physicists across our multiple sites, and versioning with timestamps was used to track changes. Conditional formatting was used to identify QC values that were outside their expected range. A Python script was utilized to trigger timely email alerts for missing QC to a qualified medical physicist (QMP) and the respective system's lead technologist for follow‐up. A dashboard was created using Excel‐based indicators in SharePoint to give an overview of the QC status of the enterprise. QC Technologists’ feedback was used to refine the system and to implement improvements, such as including guidance for performing QC directly on the form.

Results

Email alerts allow missed QC tests to be corrected the same day instead of being discovered after their due date by a technologist or by the physicist's periodic QC review. QC tests those are out of range are easily identified, and appropriate action can be taken. QC review by the QMP can be done remotely and more frequently, and preparation for regulatory inspections of QC logs has been simplified. In addition, in two cases in the first 6 months of use, failing QC values gave an early indication of tube failure.

Conclusion

Using software available at our institution, we implemented a QC system that improves efficiency for technologists, lead technologists, and the QMP by giving timely on‐screen and email‐based feedback.

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A Quality Control Monitoring Program in Digital Radiography

M Hoerner^*, A Mustafa

(1) Yale‐New Haven Hospital, New Haven, CT

Purpose

Quality control is an undervalued aspect in digital radiography imaging due to the large number of units that perform a sizable number of exams every year and the fast transition from screen‐film to digital detection and display methods. Tracking this data can be difficult. Metrics such as exam repeat rate, reject rate, and exposure index are used by the imaging community to evaluate performance of the overall practice and the radiographic imaging equipment. The goal was to develop a methodology to collect, standardize, and analyze data to produce these metrics.

Methods

Each digital radiographic device is capable of exporting data for each exam performed within a given timeframe. Every month, these data were collected and stored. Every 3 months, the data were combined and processed using a software program which organizes the data, performs calculations, and standardizes the information so that it can be analyzed. The result is a large excel file which can then be used to create pivot tables to facilitate further data analysis.

Results

Data can be organized by patient age, exam type, exposure index, number of rejects, number of repeats, unit the exam was performed on, total number of exams, technologist who performed the exam, and total repeat/reject rate. A common application compares how individual x ray units relate to one another for exposure index and repeat rejects rate for different exam types. This information identifies potential areas of improvement.

Conclusion

The results demonstrate a significant advancement for performing digital imaging quality control and properly identify areas of weakness and optimize time and effort spent in corrective actions. None of these areas would have been visible before. Technologist education and training has been implemented and has begun to result in lower radiation doses to patients, improvement in x ray imaging practice, and improved image quality.

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Shielding a High‐Sensitivity Digital Detector from Electromagnetic Interference (EMI)

D Hintenlang^*, K Little, X Jiang

(1) Ohio State University, Columbus, OH

Purpose

To document a study in shielding a high‐sensitivity digital mammography system detector from AC magnetic fields of magnitudes great enough to induce imaging artifacts.

Methods

Preliminary evaluation of AC magnetic fields at a site designated for a digital breast tomosynthesis (DBT) system raised concerns that the magnetic component of electromagnetic interference (EMI) may be great enough to induce imaging artifacts. Subsequent measurements using digital detector arrays from two separate manufacturers verified this concern, and AC magnetic fields were mapped, spatially and temporally, throughout the area of concern. A simple shielding model was developed to elucidate the physics of extremely low frequency (ELF) EMI shielding and independently verify a commercial group's proposed shielding design and installation. Post‐shielding measurements were performed to demonstrate that the EMI fields were reduced to acceptable levels.

Results

Pre‐shielding measurements showed AC magnetic fields significantly exceeding manufacturers’ tolerances for artifact‐free imaging in DBT. Continuous measurements demonstrated that the EMI fields varied significantly over time. Some locations in the room routinely averaged above 30 mG and occasionally exceeded 100 mG. The source was attributed to an adjacent electrical supply room, and temporal changes of the EMI were attributed to variations of the building electrical loads. The proposed shielding primarily consisted of continuous aluminum (1/4” nominal thickness) and was installed by a group specializing in electromagnetic field shielding. Post‐shielding measurements demonstrated that the EMI fields were significantly reduced, generally to less than 0.5 mG, and that the shielding effectively dampened the large variations due to dynamic building electrical loads. Subsequent installation and evaluation of a DBT system revealed no issues with imaging artifacts.

Conclusion

The successful shielding of ELF EMI involves physical principles that are not commonly encountered by medical physicists. Modern high‐sensitivity digital detectors may be successfully shielded against imaging artifacts with careful application of these principles.

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Implementation of Quality Assurance Program for Diffusion Weighted Imaging, Employing ACR Phantom, in Large Medical Center Setting

Y Rudzevich^1,*, E Cameron², C Lin³

(1) Indiana University School of Medicine, Indianapolis, IN, (2) Purdue University, West Lafayette, IN, (3) Mayo Clinic, Jacksonville, FL

Purpose

In this work, we present the preliminary results of DWI QA using ACR phantom on a large fleet of clinical MR scanners. We demonstrate sensitivity and feasibility of this technique.

Methods

A DWI QA procedure was integrated into the regular ACR phantom annual QA. The DWI QA protocol was scanned twice for each phase encoding direction (AP,RL). For each acquisition, three sets of images were reconstructed: source images, diffusion weighted images, ADC maps. The temperature of the ACR phantom was measured to calculate the expected ADC value. A total of 15 scanners were surveyed and analyzed. ADC Accuracy, ADC Spatial Variation, DWI Geometry Accuracy (Image Misregistration and Distortion), DWI Percent Signal Ghosting (PSG) were analyzed to evaluate the quality of DWI.

Results

The percent error of ADC value over 15 scanners was analyzed with respect to field strength and bore size. There was no statistical correlation between ADC accuracy and field strength. However, ADC values for the 60 cm bore size demonstrated clear underestimation of ADC values, while the 70 cm bore scanners overestimated ADC values with a higher absolute error (−0.77% vs. 1.12%, respectively). Absolute error of image Spatial Variation in vertical (AP) and horizontal (RL) directions were 0.59% and 0.4%, respectively. Image Misregistration and Distortion have a better performance in the horizontal (RL) direction compared to the vertical (AP Mean Shift = 0.89 mm, RL Mean Shift = 0.62 mm, AP Distortion = 0.8 mm, and RL Distortion = 0.61 mm). Mean PSG for 1.5T scanners was 1.75% while 3T showed significantly better performance with PSG = 0.76%.

Conclusion

To the best of our knowledge, this is the first time, a DWI QA procedure was tested on a large number of clinical MRI scanners of different makes and models. It can be readily incorporated in the regular weekly, monthly or annual QA tests.

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Leveraging Deep Learning Artificial Intelligence to Conduct Quality Control On Chest X Ray Images

M Zhang¹, K Nye², G Avinash¹, JM Sabol^2,*

(1) GE Healthcare, San Ramon, CA, (2) GE Healthcare, Waukesha, WI

Purpose

To develop and assess performance of artificial intelligence (AI) algorithms that perform automatic quality control (QC) checks on chest x ray images.

Methods

Over 100,000 x ray images of numerous anatomical exams and views were compliantly collected from five institutions in the USA, Canada, and China. All images had been either QC rejected on the modality or QC accepted and sent to PACS. Variational autoencoder (VAE) deep learning and convolutional neural networks (CNNs) were used to create AI algorithms to automatically perform two QC tasks. The first algorithm, a one‐class classifier using VAE and CNNs, trained to detect a single class — frontal (AP/PA) chest x ray image versus image of other anatomy. DICOM header information was used to provide initial image level labels, followed by manual review and annotation correction. The second algorithm, a binary classifier using CNNs, was trained to determine whether the patient positioning in a frontal chest x ray was acceptable. This algorithm was trained using x ray images rejected for patient positioning errors by a technologist as well as those accepted. The technologists’ self‐reported reject reasons were used as initial image level labels. Then, radiographic technologists manually reviewed and conducted annotation corrections. Performance of the algorithm for correct view and positioning were evaluated using receiver operating characteristic (ROC) analysis.

Results

Both algorithms performed very effectively; each with an ROC area‐under‐the‐curve of 0.99. The accuracies of the algorithms were 0.99 and 0.95 for the frontal chest x ray detection algorithm and patient positioning algorithm, respectively.

Conclusion

This work demonstrates the feasibility of using AI as a virtual QC technologist to determine if incorrect anatomy or view were acquired and whether patient positioning was acceptable for chest x ray images. These results warrant further development to expand anatomy and view types, and additional image reject reasons.

All authors are employees of GE Healthcare

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Using Max Standardized Uptake Value (SUV) From Positron Emission Tomography (PET) to Assess Tumor Responses After Lung Stereotactic Body Radiotherapy (SBRT) for Different Prescriptions

M Ding^1,*, W Zollinger², R Ebeling³, D Heard⁴, R Posey⁵

(1) Tulane University, New Orleans, LA, (2) Northeast Louisiana Cancer Institute, Monroe, Louisiana, (3) Northeast Louisiana Cancer Institute, Monroe, Louisiana, (4) Northeast Louisiana Cancer Institute, Monroe, Louisiana, (5) Northeast Louisiana Cancer Institute, Monroe, Louisiana

Purpose

To compare tumor responses after lung Stereotactic body radiotherapy (SBRT) using maximum Standardized Uptake Value (SUV) from 18F‐fluorodeoxyglucose (FDG) Positron Emission Tomography (PET) for different SBRT prescriptions.

Methods

Tumor responses among different SBRT prescriptions were compared by examining 48 treatments that used four different SBRT prescriptions. All SBRT patients were treated on 21iX and Trilogy machines (Varian Medical Systems, Palo Alto, CA) using RapidArc®. This study used a simplified tumor response criteria: (1) Complete Response (CR) — post max SUV (SUVpost) after SBRT in the treated tumor region was almost the same as the SUVs in the surrounding regions; (2) Partial Response (PR) — SUVpost was smaller than previous max SUV (SUVpre), but was greater than the SUVs in the surrounding regions; (3) No Response (NR) — SUVpost was the same as or greater than SUVpre. Some SUVpost reported as mild or favorable responses were classified as CR/PR. Biologically equivalent dose (BED₁₀) calculated using an α/β of 10 Gy were used in the discussions.

Results

We observed that max SUVpost at or below 1.9 showed similar max SUVs in surrounding regions for patients treated with SBRT. SUVpost ≤ 1.9 was classified as CR. The 4 SBRT prescriptions of 45 Gy @ 9 Gy × 5, 50 Gy @ 10 Gy × 5, 55 Gy @ 11 Gy × 5, and 48 Gy @ 12 Gy × 4 had 29%, 40%, 58%, and 79% CR, respectively.

Conclusion

We found that 3 month post max SUV could efficiently assess local tumor responses after SBRT. The lung SBRTs treated at our institute had very favorable tumor responses. Comparing the tumor responses among different SBRT prescriptions historically used at our institute, SBRTs delivered with a BED₁₀ > 100 seemed to result in an improved rate of CR.

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Influence of Oral Contrast Agent On Dose Calculation of Radiotherapy Treatment Planning for Pancreatic Cancer a Multi‐Factor Systematic Analysis Based On 3D Conformal Radiation Therapy and Volumetric Modulated Arc Therapy

F Zhu^*, W Wu, F Zhu, Y Wang, T Xia

(1) General Airforce Hospital, PLA, Beijing, Beijing

Purpose

To investigate the dosimetric influence of oral contrast medium used for pancreatic cancer radiotherapy treatment planning, as well as the influence intension correlated with different levels of contrast density and different radiation techniques.

Methods

Ten candidates with locally advanced pancreatic cancer and no remote metastasis were enrolled in our study. A total of 250 ml of diluted solution consisting 3% iopamidol was given orally 15 mins before CT scanning. Target volumes, normal tissues and astrointestinal contrast volume (CV) under irradiation implicated were countered on the oral contrast CT images, respectively. In our study, we simulated four branches of treatment plans as 5/7/9‐beam conformal radiotherapy (5/7/9b‐CRT) and volumetric modulated arc therapy (VMAT) for each patient. For each plan, eight QA‐plans were designed keeping all parameters the same except the HU value of CV were forced filled with eight bulk of HU value varied from 0HU(ED = 1.0) to 1000HU (ED = 1.54). Finally, dose distribution of isolate plan was compiled and compared.

Results

The analysis warranted that as CV HU enlarged from 0HU to 1000HU, the dose deviation of target volume was linearly overestimated but the percentage difference was relatively small. It shows a decline trend of dose deviation when higher modulated techniques were employed. Dose in target volume showed a relatively smaller deviation compared with that in OARs. All percentage difference was smaller than 1% and a whole picture gamma index analysis indicated 100% pass rate for 2%/2 mm criteria when CV HU<500, while in clinical the CV mean HU value is around 200.

Conclusion

The dosimetric influence of oral contrast medium for pancreatic cancer radiotherapy was clinically negligible if the enhanced electron density was controlled in a reasonable zone. The quantitative analysis indicated the dose deviation was smaller than 1% if enhancement level kept in a suitable level. Furthermore, higher modulation technique can reduce the deviation.

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A User Friendly GUI for Calculation of Radiobiological Indices and Applicator Displacements in HDR Brachytherapy

M Rahman^1,*, M Shojaei¹, S Pella^1,2, G Kalantzis¹

(1) Florida Atlantic University, Boca Raton, Florida, (2) South Florida Radiation Oncology, Boca Raton, Florida

Purpose

The aim of this project was to develop a user‐friendly GUI to calculate the applicator displacement and accelerate the process of calculation and evaluation of the EUD and EUD‐based NTCP for organs at risk in High‐Dose‐Rate (HDR) Brachytherapy.

Methods

A Graphical User Interface (GUI) was created using MATLAB to calculate applicator displacement and radiobiological parameters in HDR Brachytherapy. To calculate the applicator displacement, the coordinates were extracted using CERR and then 3D point‐cloud rigid registration method was applied to register two PTVs of interest from different fractions. Finally, translation and Euler angles were calculated to find the displacement of the applicators. Niemierko's EUD‐based NTCP mathematical model was also implemented in the GUI for easy evaluation of EUD and NTCP for organs at risk in HDR Brachytherapy.

Results

Applicator displacements were successfully calculated and expressed in terms of rotation angles and translation if available. Radiobiological Parameters such as EUD and NTCP were also calculated in a fast and user friendly interface.

Conclusion

We implemented our unique method in the GUI to calculate the applicator displacements. Niemierko's EUD‐based NTCP mathematical model was also implemented to calculate EUD and NTCP. The interface doesn't require repeated command line inputs which reduces the user errors significantly and hence it is a very friendly tool for users without programing background.

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SSIM Index for the Quantitative Evaluation of Radiotherapy Dose Distribution

C Shi^*, S Lim, M Chan

(1) Memorial Sloan Kettering Cancer Center, Basking Ridge, NJ

Purpose

To evaluate using SSIM index into plan evaluation and dose map comparison with various QA devices in radiotherapy.

Methods

Structural Similarity Index (SSIM), which measures the degree of similarity of an image to a defined reference image, is defined as the product of image luminance (L), contrast (C), and structure similarity (S) terms. In radiotherapy, luminance, contrast, and structural similarity are defined as dose deposition, device specific characteristic dosimetric noise, and the patient specific two‐dimensional dose distribution patterns, respectively. A set of IMRT QA distributions, measured with Varian EPID imager, Sun Nuclear MapCheck, and IBA Dolphin, is compared with the reference calculation generated by Varian Eclipse treatment planning System using SSIM. The same measurements are also compared with the reference distribution using gamma index. The exponent terms of L, C, S are varied systematic to assess the sensitivity of SSIM. A test pattern with 1 mm distance shift and 2% dose difference has been benchmarked using SSIM index and gamma index, respectively, for the following three scenarios: (1) distance shift 1 mm alone; (2) dose difference 2% alone; and (3) background 2% alone. SSIM indexes have been calculated to show the comparison of those images, as compared to those used with gamma index.

Results

The test pattern shows that SSIM index could detect the minor changes in distance, intensity, and contrast rather than gamma index. The comparison also indicates different qualities of the dose map from different QA devices. Though a clinically relevant tolerance for the SSIM index has not yet been determined, the results show that the SSIM index is more sensitive to image/fluence/dose from different QA modalities.

Conclusion

We have investigated a new evaluation metric for dose distribution and device comparison — SSIM index. SSIM index has the potential to be implemented into radiotherapy QA.

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Assessment of Setup Error Correction of Total Marrow Irradiation Using ‘interrupt‐Scan‐Registration’ MVCT Image Guided Registration

F Zhu, D Chang, W Wu, Y Wang^*, T Xia^*

(1) General Airforce Hospital, PLA, Beijing, Beijing

Purpose

To investigate the setup errors recorded with multi‐times ‘interrupt‐scan‐registration’ MVCT image guided registration scheme, and evaluate the feasibility of this method.

Methods

Twenty‐one patients performed TMI treatment from 2014‐03 to 2016‐05 were enrolled in our study. The image guided registration during treatment was divided into three sections for upper body treatment. First, a MVCT scan was conducted in the central region of Head&Neck (HN) part using normal mode, then register the MVCT images with original planning CT image using bone anatomy alignment method automatically then manually. After registration and couch shift we started the irradiation. When approaching to about 1/3 of the treatment, we interrupted and did a second scan in the region of Thorax&Abdomen (TA) region. To avoid the dose mismatch at the interrupt slice, the Y axis shift must be reset to zero. Reprocess this operation at 2/3 of the treatment in the region of Pelvic(p) region. For lower extremities plan, one MVCT image registration was performed only.

Results

The shift average of (X,Z) axis are (−0.45 ± 2.24 mm, 0.24 ± 4.39 mm) for HN, (0.12 ± 2.68 mm, −0.83 ± 2.44 mm) for TA, (0.25 ± 3.5 mm, −0.24 ± 1.90 mm) for P, and (−0.64 ± 2.44 mm, 0.51 ± 2.56 mm) for lower leg. The percentage that X shift falls into the interval of (−3, 3)mm, (−5, 5)mm and (−5, 5)mm is 84.13%, 92.06%, 85.71% for upper body, respectively, for Z shift are 63.4%, 93.6%, 98.4%, respectively. The backward original setup error shows that the setup error of (X,Z) are (0.62 ± 3.05 mm, −0.57 ± 4.22 mm) for T&A region, and (0.38 ± 3.94 mm, −0.82 ± 4.23 mm) for P region.

Conclusion

The original setup error before treatment is significantly large, especially in the adjacent tail end. ‘interrupt‐scan‐registration’ MVCT registration scheme would substantially reduce the variance of setup error feasibly, while compared with conventional cancer radiotherapy the shift is still vast. Results also imply that the PTV margin from bone should be defined in a cautious way.

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Temporally Feathered Intensity Modulated Radiation Therapy: A Technique to Reduce Normal Tissue Toxicity

S Parsai^1,*, J Alfonso², J Donaghue³, N Joshi⁴, A Godley⁵, C Shah⁶, S Koyfman⁷, J Caudell⁸, C Fuller⁹, H Enderling¹⁰, J Scott¹¹

(1) Cleveland Clinic, Cleveland, Ohio, (2) Helmholtz Centre for Infection Research, Braunschweig, (3) The Cleveland Clinic Foundation, Cleveland, OH, (4) Cleveland Clinic, Cleveland, Ohio, (5) The Cleveland Clinic, Cleveland, OH, (6) Cleveland Clinic, Cleveland, Ohio, (7) Cleveland Clinic, Cleveland, Ohio, (8) Moffitt Cancer Center, Tampa, FL, (9) MD Anderson Cancer Center, Houston, TX, (10) Moffitt Cancer Center, Tampa, FL, (11) Cleveland Heights, OH

Purpose

We introduce a novel strategy of radiotherapy planning using canonical radiobiology principles, idealizing fractional doses and timing delivered to organs at risk (OAR) to decrease normal tissue complication probability (NTCP). This strategy is termed temporally feathered radiation therapy (TFRT). A dynamical model of normal tissue radiation response with respect to tissue recovery is used to compare TFRT and conventionally fractionated radiotherapy.

Methods

Dynamic NTCP modeling was performed to simulate the cumulative effects of normal tissue damage and recovery. Normal tissue damage was determined by the Linear‐Quadratic (LQ) model. TFRT plans were generated by altering the fractional dose delivered to normal tissues. Each OAR receives a rotation of a higher than standard dose of radiation (DH) once weekly followed by lower than standard doses (DL) the remaining four fractions that week. We developed a term, “success potential”, to demonstrate reduction in NTCP with TFRT as compared to conventional RT under various recovery rates and standard daily fractional doses. Finally, we created patient‐specific plans using TFRT through RayStation treatment planning system, creating in silico models of head and neck plans treated to 70 Gy in 35 fractions.

Results

TFRT is beneficial in reducing toxicity compared to conventional RT schemes. Delivering a combination of DH and DL to OARs allows increased sublethal damage recovery despite higher total radiation doses delivered to OARs. The magnitude of clinical benefit of TFRT plans is dependent on the standard dose delivered to OAR with conventional plans as well as the organ‐specific recovery rate of radiation damage.

Conclusion

TFRT offers a novel technique for radiation planning optimization. Application of this technique to carefully selected cases can reduce normal tissue toxicity. With widening of the therapeutic ratio, isotoxic radiation therapy plans can be delivered in an effort to allow dose intensification to the target volume.

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Comparing Results from a Single Vendor's Patient QA Solutions

S Mitchell^*

(1) West County Radiological Group, Saint Louis, MO

Purpose

To investigate results from initial usage of DoseCHECK, PerFRACTION, and ArcCHECK patient QA products from Sun Nuclear Corporation (SNC).

Methods

At a new clinic, the first 23 VMAT patient plans (RayStation TPS and Elekta Infinity linac) were selected for analysis of pass‐rate consistency among multiple patient pre‐treatment QA products offered by SNC. For each patient, gamma analysis criteria across products were consistent (typically 3%/3 mm/10% threshold). The investigated products were: (1) DoseCHECK (3D dose calculation engine using the patient CT, RT Structure Set and RT Plan from the TPS) [dc3d]; (2) PerFRACTION 3D with logs only (3D dose calculation engine using the patient CT, RT Structure Set, RT Plan and log files created using an iCom interface to the linac during delivery) [pf0logs]; (3) PerFRACTION 3D with EPID (CT, RT Structure Set, RT Plan, logs and EPID images captured by the Elekta iView panel to verify actual MLC position) [pf0epid]; and (4) ArcCHECK [ac]. Reference dose for analysis was either the TPS dose on the patient CT (for [dc3d], [pf0logs], [pf0epid]), or TPS dose on the ArcCHECK phantom (for [ac]).

Results

The Friedman rank sum test yielded a p‐value ≤ 0.0001 indicating a difference among product performances. Linear correlation (R² = 0.994) was observed between [dc3d] and [pf0logs] for the paired sample. In keeping with the statistical testing, visual examination of pass‐rate performance for [pf0epid] vs. [dc3d], [ac] vs. [dc3d], and [ac] vs. [pf0epid] all illustrated little discernible correlation with R² ≤ 0.2 for all.

Conclusion

EPID image usage introduced a marked PerFRACTION performance difference from that obtained using log files only. ArcCHECK performance was uncorrelated with PerFRACTION 3D regardless of EPID image usage. Future work will investigate 2D performance of PerFRACTION 2D using an EPID calibrated for absolute dose and calibration technique influence upon ArcCHECK.

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A Survey of the Physics Initial Plan Review Process

G Salomons^1,*, G Chan², L Chin³, H Keller⁴, K Nakonechny⁵, C Neath⁶

(1) Cancer Center of Southeastern Ontario, Kingston, ON, (2) Juravinski Cancer Centre, Hamilton, Ontario, (3) Sunnybrook Health Sciences Centre, Toronto, Ontario, (4) The Princess Margaret Cancer Centre — UHN, Toronto, ON, (5) Simcoe Muskoka Regional Cancer Centre, Barrie, ON, (6) R.S. McLaughlin Durham Reg Cancer Ctr, Oshawa, ON

Purpose

We report on some of the results of a survey of the physics plan review process. Two goals of the survey were to: identify which elements of a treatment plan are being checked by a physicist and; to determine the variation in practice for treatment plan reviews.

Methods

The Chart Checking Practices Group, commissioned by Cancer Care Ontario, conducted the survey at the beginning of 2015. The medical physics departments at each Ontario cancer centre completed the survey in a group setting, submitting a single response from that centre. Questions addressing which elements of a patient's plan are being checked by the physicists asked the groups to indicate if: “All”, “Most”, “Some”, or “None” of the physicists in the group performed that particular check.

Results

Only two of 42 items, bolus and heterogeneity, were reported as checked by “All” physicists at all centers. Eleven items were reported as checked by “All” or “Most” of the physicists. The only item that more than half of the centers reported “None” of their physicists check was DVH bin resolution. A total of 37 of the 42 items were reported as checked by “All” or “Most” of the physicists at more than half of the centers. In general, the least checked items related to setup and imaging.

Conclusion

There is a sizable degree of variability in plan review both between centers and between individual physicists in the same center. The use of a standardized checklist does not reduce this variability, but may improve the physicists’ awareness of the existing variability.

This work was funded by Cancer Care Ontario

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Using TG‐132 Digital Phantoms to Compare Registration Results Between the MIM Maestro and Raystation Systems

J Pursley^*

(1) Massachusetts General Hospital, Salem, MA

Purpose

The report from AAPM Task Group 132 was published in July 2017 with recommendations for validation of image registration algorithms, and included a set of digital phantoms to assist with validation tests. In this work, those tests and phantoms were used to validate and compare the registration results from two clinical software packages, MIM Maestro and the Raystation treatment planning system.

Methods

The software versions used for this work were MIM Maestro 6.7.10 and Raystation 5.0.3, both of which were previously commissioned for clinical use. Digital phantoms were downloaded from the TG‐132 website and imported into both systems. Recommended tests from the TG‐132 report were performed in each system. For rigid registrations, the translations and rotations given by each system were compared to the expected values. For deformable registrations, registrations were examined visually and, where available, quality metrics were applied on the deformation vector fields, landmark analysis, or contour deformation.

Results

Both systems performed acceptable rigid registrations on all TG‐132 digital phantoms, which included registering phantoms simulated with different imaging modalities (CT, T1 MR, T2 MR, PET, and CBCT). Both systems gave results closer to the expected values when performing intramodality registration (CT to CT or CBCT) than for intermodality registration (CT to MR or PET). The deformable registration process relies more on user input than rigid registration and the results are difficult to quantitate even for phantoms, but both systems performed similarly on the TG‐132 recommended deformable registration tests.

Conclusion

MIM Maestro and Raystation 5.0.3 performed acceptable rigid and deformable registrations by TG‐132 criteria. The TG‐132 commissioning exercises were helpful to learn the strengths and limitations of each system, and particularly useful as a tool to learn what registration options are available in each system and how they can be used to improve registration results.

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Quantification of TG 119 in the VMAT Era

JE Roring^*, K Rasmussen, S Stathakis, D Saenz, N Kirby, N Papanikolaou

(1) UT Health San Antonio, San Antonio, TX

Purpose

TG — 119 provides a set of IMRT commissioning tests to assist with inter‐clinic quality standards in Intensity Modulated Radiation Therapy. Outcomes from TG — 119 were based on Step and Shoot IMRT plans using only 6 MV beams. Modern IMRT has evolved toward Volumetric Modulated Arc Therapy and can incorporate a wide range of energies. The purpose of this work was to compare plans between multiple linacs to the established data using multiple energies with both IMRT and VMAT.

Methods

The plans were created on the Pinnacle3 treatment planning system using Varian Novalis Tx and Elekta VersaHD linear accelerator models. All plans meet the dose constraints as designated within TG – 119. Treatments were recalculated to be delivered to the PTW Octavius4D phantom for measurement. The Gamma passing rate was determined using PTW Verisoft.

Results

MultiTarget gamma index pass rates within 3%/3 mm were 95.7% for 6 MV IMRT and 97.4% for 6 MV VMAT. The prostate plans passed with 95.6% for 6 MV IMRT, 98.3% for 6 MV VMAT, 95.0% for 10 MV IMRT, and 98.4% for 10 MV VMAT. VMAT plans within Pinnacle3 allowed for more homogeneous distribution within the target (smaller cold and hot spots) and reduced overall dose to organs at risk.

Conclusion

VMAT plans produced similar desired treatment results to IMRT plans with gamma passing at a slightly higher rate. Six and 10 MV were able to create similar plans for the phantom tested and show no significant difference in gamma passing rate. It is important to verify that VMAT accuracy is as acceptable as that of previous IMRT plans. This work allows for the development of more accurate IMRT delivery and verification of current quality assurance standards within the clinic.

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Photon Beam Profile Deconvolution for Fields with and Without the Flattening Filter Using a Neural Network

H Liu^1,*, F Li¹, J Park¹, S Lebron¹, J Wu¹, B Barraclough², J Li¹, C Liu¹, G Yan¹

(1) University of Florida Health Science Center, Gainesville, FL, (2) University of Wisconsin, Madison, WI

Purpose

To deconvolve volume averaging effect (VAE) of ion chambers (IC) in beam profile measurement using neural network (NN) and to investigate whether separate NNs for flattening filter (FF) fields and flattening filter free (FFF) fields are necessary.

Methods

A feed‐forward NN with a hidden layer and an output layer was trained with profiles measured with an IC and a diode. The hidden and output layer used tan‐sigmoid and linear transfer function, respectively. A sliding window was used to extract input data for the NN from the IC‐measured profiles. The diode measurement at the center of each sliding window was used as the desired output. The NN, trained with a Levenberg Marquardt‐based backpropagation algorithm, output a deconvolved value for each sliding window. We optimized the size of the sliding window (SSW) and the number of hidden neurons (NHN) as hyperparameters. Separate NNs were trained for FF and FFF fields, respectively. Combined NNs were also trained with both FF and FFF profiles. Their performance was evaluated by the penumbra width difference (PWD) between the predicted and diode‐measured profiles.

Results

For the separate NN for FF fields, minimal mean PWD of 0.03 mm was achieved with SSW= 9 and NHN = 7; for FFF fields, minimal mean PWD was 0.02 mm when SSW = 7 and NHN = 7. The performance of the combined NN was similar with the minimal mean PWD for FF and FFF fields being 0.05 and 0.03 mm, respectively, when SSW = 9 and NHN = 7. Separate NNs predicted slightly smoother beam profiles than the combined NNs for small FFF fields (2 × 2 cm2).

Conclusion

NNs are accurate and efficient tools to minimize VAE of IC in beam profile measurement for both FF and FFF fields. It is not necessary to train separate NNs for FF and FFF beam fields.

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A Practical Method for the Reuse of NanoDot OSLDs Up to at Least 50 Gy

A Zhuang^1,*, A Olch^1,2

(1) USC Keck School of Medicine, (2) Childrens Hospital of LA, Los Angeles, CA

Purpose

OSLDs are used to make in vivo measurements (i.e., TBI, TSEI). Most users calibrate the OSLDs using the software provided by Landauer, which typically covers doses up to about 3 Gy. OSLDs that reach that dose are discarded and new ones purchased and calibrated each. We have developed an accurate method of reusing OSLDs up to at least 50 Gy and may be applicable far above that dose.

Methods

Instead of using the calibration routine in the InLight microStar software (Landauer, Inc.), we anneal them with a fluorescent light source to less than 200 counts (˜0.3 cGy), irradiate them with 50 cGy, and use the hardware mode in the software to read OSLDs to produce an OSLD serial number‐specific calibration factor. After total body irradiation delivery, we read them in hardware mode and apply the calibration factor to get the dose. We then repeat this process for the next usage. In this study, we retrospectively analyzed the measured calibration factors vs. accumulated doses for nine OSLDs irradiated up to 29 times to nearly 50 Gy total dose. All OSLD's responded linearly with dose with the value of R2 between 0.95 and 0.98. With this finding, we propose an efficient and accurate method to reuse OSLDs with intermittent recalibration with less than 5% maximum error.

Results

Within the 29 uses, sets of three predicted calibration factors were compared to the measured calibration factors. The average precision was 1.9% ± 0.58%, 2.27% ± 0.74%, 2.96% ± 0.52%, and 3.64% ± 0.78%.

Conclusion

Our method is a cost‐saving and feasible method that allows a user to reuse an OSLD up to at least 50 Gy accumulated dose with minimal recalibration effort, and predict calibration factors with a precision better than the 5% value one can achieve with the conventional batch calibration method.

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An Approach to Improved MLC Transmission Modeling for Highly‐Modulated Treatments in Pinnacle Treatment Planning System

D Heins^1,*, E Grant², C Large³

(1) CARTI, Inc., Little Rock, AR, (2) CARTI, Inc., Little Rock, AR, (3) Philips Healthcare, Fitchburg, WI

Purpose

To develop a novel approach for determining optimum values for MLC transmission, additional interleaf leakage, and tongue and groove width that will improve modulated beam modeling in Pinnacle TPS v9.10 for 6 MV, 6 MV‐FFF, 10 MV, and 10 MV‐FFF photon beams.

Methods

Open and MLC closed fields were measured using EDR2 film for Varian TrueBeam Linac with Millennium 120 MLC. Calibration curves were used to convert the films from intensity to absolute dose. The ratio of MLC matrix to open matrix was calculated. The average of every column of data was determined along the direction of the MLCs. This resulted in a single average dose profile of interleaf leakage and MLC transmission. The peaks (interleaf leakage) and valleys (MLC transmission) were averaged together to get the final average interleaf leakage and MLC transmission. Finally, the tongue and groove width was estimated dosimetrically by the FWHM for each period. A final correction for additional interleaf leakage was applied to the model.

Results

We compared gamma pass rates from measurements of 14 VMAT arcs and 75 IMRT fields covering a range of anatomical sites. The new model was compared to the current model by analyzing the mean pass rate in percentage points. The most dramatic improvement in pass rates was observed in 10 MV VMAT arcs with an improvement of 23.5 percentage points using gamma criteria of 2%/2 mm without Van Dyk and the lowest improvement of 0.5 percentage points for 6 MV‐FFF VMAT using gamma criteria of 3%/3 mm with Van Dyk. IMRT fields showed little improvement with minimal degradation of pass rates.

Conclusion

This study has demonstrated a novel and thorough method for measuring and implementing improved values required by Pinnacle TPS. The results showed marked improvements in gamma pass rates for highly modulated fields with little change in pass rates for lightly modulated fields.

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Concurrent 3D Isocentricity Analysis for Clinical LINACs

C Velten^1,*, YF Wang², PJ Black², J Adamovics³, CS Wuu^1,2

(1) Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY, (2) Department of Radiation Oncology, Columbia University, New York, NY, (3) Department of Chemistry, Biochemistry, and Physics, Rider University, Skillman, NJ

Purpose

To perform three‐dimensional (3D) isocentricity test of a medical linear accelerator (LINAC) using a 3D dosimeter (PRESAGE). The test includes the isocenter size and position measurement for gantry and couch rotations, whose precise knowledge is important for the accurate delivery of non‐coplanar treatment plans.

Methods

A 3D dosimeter was setup on the treatment couch of a Varian TrueBeam LINAC and the coincidence with the setup lasers was marked using metal ball bearings. Irradiations were performed under gantry angles of 0°, 50°, 160°, and 270° with the couch fixed at 0° and subsequently, under couch angles of 10°, 330°, 300°, and 265° with the gantry fixed at 270°. The 1 cm2 (at 100 cm SAD) square fields were delivered at 6 MV with 800 MU/field. After irradiation the dosimeter was scanned using a single‐beam optical scanner and images were reconstructed with sub‐millimeter resolution using filtered back‐projection. The stack of reconstructed images was rotated in 3D to extract stacks perpendicular to the gantry and couch rotation axes showing the star shots. Beam trajectories and the smallest circle enclosing these were drawn and extracted from both images. Information from the third orthogonal stack was used for 3D localization.

Results

The gantry and couch rotation isocenter diameters were measured to be 0.41 mm and 0.70 mm while the distances to the setup center in 2D/3D measured 1.30/1.73 mm and 0.16/0.72 mm, respectively. The isocenter sizes as well as the 2D couch isocenter distance agree with the film measured values. The gantry isocenter distance, however, was not reproducible and is likely due to a setup center registration error.

Conclusion

This study demonstrates that 3D dosimeters can be used to concurrently measure isocenter sizes and their position with appropriate procedure and provides more information than 2D measurements.

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Clinical Implementation and End‐To‐End Testing of Varian SRS Cones

C Hand^1,*, C Fitzherbert¹, F Zhou¹, P Irmen²

(1) Albert Einstein Medical Center, Philadelphia, PA, (2) University of Pennsylvania, Philadelphia, PA

Purpose

Due to limited industry guidelines for small field dosimetry, this study will demonstrate the clinical implementation and end‐to‐end testing of Varian SRS cones.

Methods

6 MV and 6 FFF plans were created for each of the Varian SRS cones (17.5 mm, 15 mm, 12.5 mm, 10 mm, 7.5 mm, 5 mm, and 4 mm) in Eclipse Cone Planning. Each plan consisted of a 50° and 80° arc. A water phantom was used for calculation at 95 cm SSD. Point doses were calculated on the central axis at 5 cm depth. Point doses were measured and verified using a PTW 60012 in a Sun Nuclear 1D SCANNER water tank and a Sun Nuclear EDGE detector in both a solid water phantom and 1D SCANNER water tank. In addition, independent MU and dose verification was performed using RadCalc® software for each plan.

Results

For the EDGE detector, the maximum difference between the planned point dose and the measured point dose was 3.19% and 1.26% for 6 MV and 6 FFF energies, respectively, using a solid water phantom and 6.77% and 3.72% for 6 MV and 6 FFF energies, respectively, using a water tank. For the PTW 60012, the maximum difference between the planned point dose and the measured point dose was 2.38% and 6.92% for 6 MV and 6 FFF energies, respectively. The RadCalc® software showed agreement within 1.29% for MU and 1.28% for point dose calculations for 6 MV energy plans and 0.67% for MU and 0.67% for point dose calculations for 6 FFF energy plans.

Conclusion

Recently published MPPG 9a is currently the only guideline specific to SRS/SBRT treatment but gives no detailed instruction to small field considerations. IAEA TRS 498 is referenced but is currently unpublished. This experience provides a model for successfully implementing Varian SRS cones for clinical use and developing a second independent MU and dose verification method utilizing the widely used RadCalc® software.

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On the Development of Computational Methods to Aid in Performing Medical Physics Tasks Leveraging Portal Dosimetry Application

E Rrokaj^1,*, M Schmidt²

(1) University of Nevada, Las Vegas, (2) Varian Medical Systems — Education Department, Las Vegas, Nevada

Purpose

To develop software that can programmatically analyze dosimetric images and reduce QA time when performing the Winston‐Lutz test and to determine the isocenter wobble of the linear accelerator (Varian TrueBeam).

Methods

Dosimetric images of the Winston‐Lutz test were acquired with a TrueBeam linear accelerator and loaded into a custom software application by use of the Eclipse Scripting Application Programming Interface (ESAPI) for Portal Dosimetry. The software application will allow the user to determine the center of the cone and ball to determine the coincidence of the BB with the isocenter or determine the coincidence of the BB from central axis automatically. To test the precision of this tool a set of images with known shifts were taken at gantry angles (0, 90, 180 and 270 degrees) using a 17.5 mm Conical Collimator delimited field with 100 MU per dosimeteric image at a dose rate of 300 Gy/MU and 6X photon energy. The images were programmatically analyzed and the shifts were calculated. The known shift and the calculated shift were then compared.

Results

Image analysis indicates that the software program calculates the shifts with an error less than 0.5 mm. Further tests indicate that the isocenter size can be determined using this tool within close relation to other open‐source Winston‐Lutz test analysis application.

Conclusion

This work indicates that a custom‐made software application can be beneficial when performing QA to check for the mechanical stability of the rotation axes of the linac. The analysis time recorded for this test was greatly reduced from a manually analysis performed of the same image.

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Feasibility of the DP‐850 Phantom as an Annual End‐To‐End Testing Device

L Helinski^1,*, B Murray², S Goetsch³

(1) OMPC, Chillicothe, AA, (2) OMPC Therapy, LLC and OMPC Diagnostics, LLC, Columbus, OH, (3) San Diego Medical Physics, Solana Beach, CA

Purpose

I evaluated the DP‐850 phantom as a multi‐use tool for the use in the end‐to‐end testing process to evaluate image quality, treatment planning system (TPS) accuracy and dose delivery accuracy.

Methods

The assessment was conducted out of nine separate clinical facilities, utilizing five different linear accelerators and with two types of TPS software. The end‐to‐end testing included a CT sim of the DP‐850 with an ion chamber in the center, generating test plans in the TPS, and delivering those plans to the phantom. Various image quality factors were verified at the CT simulator and the TPS. Dose accuracy of the TPS was confirmed by use of the ion chamber and the phantom as the patient. The sample plans included: 3D, IMRT, and VMAT. The IMRT/VMAT plans were created with generic optimization values to a contoured target within the phantom, this served to verify the IMRT/VMAT dose algorithms. The procedure was repeated separately for each facility evaluated.

Results

The images were successfully transferred from the CT simulators to the TPS with the correct orientation and image information. The image quality and accuracy verification testing performed on each CT scan was within acceptable limits, with no visible errors or degradation of image quality. The treatment plans were prepared in the record and verify system and were confirmed to be accurate in the treatment delivery system. The dose calculation accuracy of the TPS was confirmed by obtaining the mean dose to the contoured ion chamber volume during treatment delivery. Most results were measured below 5%, with the exception of the four‐field box when utilizing two different energies.

Conclusion

The DP‐850 phantom was found to be an acceptable device to perform annual end‐to‐end testing for all aspects of treatment planning including importing CT data sets, dose calculation, IMRT planning, and exporting treatment data.

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A Dosimetric Comparison of Lung Treatment Plans Using High Definition MLC and Standard MLC

M Pudasaini^1,*, N Dumitru², M SHOJAEI³, S Pella⁴

(1) Florida Atlantic University, Boca Raton, Florida, (2) Boca Raton, FL, (3) Florida Atlantic University, Boca Raton, Florida, (4) Florida Atlantic University & South Florida Radiation Oncology, Boca Raton, Florida

Purpose

TrueBeam becomes the linear accelerator of choice in the present years. The two models available are with high definition multi leaf collimation with 2.5 mm thick MLC for the central 10 cm × 10 cm fields size and 5 mm thick MLC for the first 10 cm × 10 cm field size. We want to show the significance of this difference and methods to minimize it via optimization procedures.

Methods

Twenty‐five patients were chosen that were treated for lung lesions using SBRT with 3–5 high dose fractions. The patients were chosen from two different centers who are using the two TrueBeam types. New plans were generated in using the type of MLC that was not used in the initial plan applying identical optimization parameters. A dosimetric analysis has been performed for the two plans and a radiobiological analysis. We compared the biological effective dose (BED), the equivalent uniform dose, the tumor control probability for lung lesions and the normal tissue complications probability (NTCP) for the healthy lung and the surrounding healthy tissue. The homogeneity of the dose distribution, the conformity and the conformality indexes were evaluated.

Results

A considerable improvement in planning target volume (PTV) coverage has been seen and a better dose distribution uniformity in the PTV in the treatment plans that used the HD‐MLC. We could not detect the same degree of improvement to the normal tissue surrounding the PTV. The dosimetrical differences due to the use of these two types of MLCs are significant in lung treatment plans.

Conclusion

PTV coverage and its dose distribution uniformity when using the HD‐MLC make the TrueBeam machine that carry those, a better tool in radiation therapy. The normal structures did not display a significant dose distribution improvement. Changing optimization constraints, we can improve the outcome to the normal tissue.

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Three‐year Experience of Electronic Portal Image Device Based Daily QA for Photon Radiation Beams

B Cai, Y He, D Bollinger, R Morris, S Goddu, S Mutic, B Sun^*

(1) Washington University School of Medicine, St. Louis, MO

Purpose

To review and analyze 3 years’ EPID based daily QA results of photon beams on a Varian TrueBeam linac.

Methods

An in‐house designed EPID based QA strategy was deployed clinically to test machine daily performance before treatment. Beam dosimetic parameters, such as output, flatness, symmetry, uniformity, TPR20/10, MLC field delivery repeatability, as well as image quality metrics, e.g., high‐ or low‐contrast resolutions, were accessed based on MV and kV EPID image analysis. Three‐year data were collected and analyzed. Trend analysis with data visualization, comparisons to ionization chamber (IC) results and QA failure studies were performed to evaluate the reliability and robustness of the EPID based daily QA system.

Results

The EPID output tests over the 3‐year period agreed with the monthly QA IC system within 1.3% and TG51 results within 1%. A consistent positive output drifting was detected for all energies over the time. A faster drifting speed was observed after the installation of a new dose monitoring chamber but slowed down over the time. Symmetry, flatness, and uniformity were stable and the changes were directly related to beam steering and the imager calibration. TPR20/10 is not sensitive to dosimetry fluctuations and a good delivery repeatability of MLC fields was observed. The image quality metrics were also stable and a failure rate around 2% was observed. Based on QA failure analysis, efforts were made to improve the robustness of the process, such as staff training, algorithm modification, and tolerance adjustment.

Conclusion

The three‐year data indicate the EPID based process is an efficient and reliable QA solution for daily linac performance check. The long‐term trend analysis and data visualization helps physicists understand the behavior of linac, optimize daily QA procedure and has the potential to predict machine failures ahead of incidents.

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A Feasibility Study of Using SGRT for Esophagus Tumors

W Jiang^*, D Cao, V Mehta, D Shepard

(1) Swedish Cancer Institute, Seattle, WA

Purpose

To evaluate the feasibility of using surface guided imaging system for patient positioning as an alternative of cone‐beam computed tomography(CBCT) and for motion tracking during the treatment in Lateral(L/R), Longitude (S/I), and Vertical(A/P) directions.

Methods

A total of 97 fractions from four patients underwent 3DCRT and IMRT in Elekta VersaHD were randomly selected. The margins expanded from the targets were from 5 mm to 10 mm. Before each fraction, patients were aligned with three‐point subcutaneous tattoos and the planned shifts were implemented manually by the therapists. A CatalystHD surface mapping system was firstly used to capture the patient's fractional setup error. The kV‐CBCT was acquired immediately following to adjust for any residual corrections. The differences between the setup errors obtained from CatalystHD and CBCT were retrospectively compared. Patients’ motions were monitored during the treatment and recorded as a total of 15449 tracking points by the CatalystHD. The ranges of motions were statistically analyzed.

Results

The average differences between the setup errors obtained from CatalystHD and CBCT were −2.0 ± 3.6 mm, −0.9 ± 4.6 mm, −1.4 ± 5.2 mm, and −2.8 ± 2.8 mm for L/R,S/I,A/P, and 3D shift vectors, respectively. The ratios of the difference less than 10 mm were 97.9%,99.0%,94.8%, and 100% for L/R,S/I, A/P, and 3D shift vectors, respectively. The ratios of the motion more than 5 mm were 0.7%, 2.6%, 4.1%, and 11.0% for L/R,S/I,A/P, and 3D shift vectors, respectively. The average motions were −0.2 ± 1.4 mm, 0.1 ± 1.7 mm, −0.4 ± 2.2 mm, and 2.4 ± 2.0 mm for L/R, S/I, A/P, and 3D shift vectors, respectively. The maximum motions for L/R,S/I,A/P directions were 8.1 mm, 10.3 mm, and 11.4 mm, respectively. 3D shift vectors showed good correlations with treatment time(R = 0.91).

Conclusion

This study shows that CatalystHD can be a periodical alternative of CBCT for esophagus patient setup if the target has a margin larger than 10 mm. Special cautions should be taken for the case with a smaller margin. The intra‐fractional motions vary and have significant deviations, which should be monitored during the treatment. To use a small margin for the target, the treatment time should be reduced.

This work was supported by Elekta AB, Stockholm, Sweden.

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Electron Monte Carlo Dose Calculation Model Dependency On Optional Applicator Specific 1D Profiles

R Sharp^*

Purpose

To determine if the inclusion of optional in air profile scans impact the output of the electron Monte Carlo (eMC) and to determine if the inclusion of the profiles is clinically relevant.

Methods

Beam scan data required to configure the electron Monte Carlo algorithm was acquired. The required data, an open field (40 × 40 cm²) PDD in water, a PDD in water with each applicator installed, and a profile in air at 95 cm distance from the radiation source. Also, optional measurements of in air profiles at 95 cm source to detector distance (SDD) with the jaws set to corresponding position of the applicator field size without the applicator installed were measured. These data were imported into the Eclipse Treatment Planning System to generate two versions of the eMC algorithm, one with and one without the optional air profiles. Each algorithm was used to calculate dose distributions in a virtual water phantom created in Eclipse. This includes varying field sizes, energy, and applicators.

Results

Initial comparisons in each version of the configured algorithm via gamma analysis indicates differences in the dose profiles.

Conclusion

The results of this work will determine if a physicist should consider taking the time to measure the in air profiles required during commissioning of the Eclipse treatment planning system. In addition, this work will quantitate the differences between the two algorithms and if the inclusions of the optional scans impact the output greatly.

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Benchmarking Techniques for Stereotactic Body Radiotherapy to Early‐Stage Glottic Laryngeal Cancer: LINAC‐Based Non‐Coplanar VMAT Vs. Cyberknife Planning

Y Zhang^*, T Chiu, J Dubas, Z Tian, P Lee, X Gu, D Sher, B Zhao

(1) UT Southwestern Medical Center, Dallas, TX

Purpose

To compare the dosimetric characteristics of larynx SBRT plans generated using LINAC‐based non‐coplanar VMAT technique and Cyberknife technique.

Methods

Ten patients diagnosed of cTis‐T2N0M0 glottic larynx carcinoma were studied. All patients have been planned and treated on the Cyberknife system with a prescribed dose of 42.5 Gy/5 fractions to the involved hemilarynx. Plans were delivered using fixed‐cone due to small PTVs. For each patient, a four‐arc non‐coplanar VMAT plan was retrospectively designed in Eclipse™ to evaluate the feasibility of treatments using conventional LINACs. Dose engine was Monte‐Carlo for Cyberknife and AcurosXB for Eclipse to achieve accurate dose calculation of PTVs with air cavity. Dosimetric comparisons were performed between VMAT and Cyberknife plans using metrics including PTV coverage, prescribed isodose lines (normalized to global maximum dose), and maximum doses to various OARs. Statistical significance was assessed using Wilcoxon signed‐rank test.

Results

The LINAC‐based VMAT technique achieves similar dosimetric endpoints as the Cyberknife planning. The PTV coverages of VMAT and Cyberknife plans are 95.0% and 95.6%, respectively. The corresponding mean prescribed isodose lines are 86.3% and 85.9% (P > 0.6). The Cyberknife plans have slightly better conformity index than the VMAT plans (1.19(Cyberknife) vs. 1.29(VMAT), P < 0.04). The average maximum doses to carotid arteries (12.3 Gy(VMAT) vs. 13.9 Gy(Cyberknife), P > 0.3) and skin (41.6 Gy vs. 41.5 Gy, P > 0.3) are similar. The VMAT plans better spare the contralateral arytenoid than the Cyberknife plans (16.0 Gy(VMAT) vs. 18.1 Gy(Cyberknife), P < 0.04). The Cyberknife plans incur less dose to the spinal cord (8.1 Gy(VMAT) vs. 5.8 Gy(Cyberknife), P < 0.02), both however are well below the tolerance of 28 Gy. VMAT uses less than 1/3 of the total MUs of Cyberknife plans and halves average treatment time (˜20 min vs. 40 min, excluding pretreatment setup). Planning time is much shorter with VMAT.

Conclusion

Larynx SBRT can be conducted on either Cyberknife or conventional LINAC with dosimetrically equivalent target coverage and similar OAR sparing.

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Correlation Between Breast Volumes and Heart Doses for Left‐Sided Whole Breast Treatment in Photon and Proton Radiation Therapy

J Yu^*, A Gutierrez, M Fagundes, M Mehta

(1) Miami Cancer Institute, Miami, FL

Purpose

To investigate if a correlation exists between treated breast volumes and heart doses for left‐sided whole breast treatment in photon tangent field‐in‐field (FinF) and proton pencil beam scanning (PBS) therapy.

Methods

For thirty left‐sided breast cancer patients, seventeen patients were treated with FinF modality using free‐breathing (FB). The FinF plans were also generated on breath‐hold (BH) CTs. Thirteen patients were treated with proton therapy with FB, and the PBS plans were created with one or two enface beams with a single field optimization technique. Volumes of whole breast PTV and heart mean dose were used for analysis.

Results

For the FinF modality treated with FB, when the breast PTVs were larger than 1000 cc, the average value of heart mean dose was 3.6 ± 0.4 Gy, and when the volumes were less than 1000 cc, the average value of heart mean dose was 2.0 ± 0.5 Gy. Differences between the two groups were statistically significant (P* = 0.036). For the FinF treated with BH, the average heart mean doses were 1.6 ± 0.2 and 1.0 ± 0.2 Gy for the PTVs larger and smaller than 1000 cc, respectively (P* = 0.0237). For proton PBS, however, there were no differences in heart doses between the two groups (P = 0.7). For all patients, the average heart mean doses were 3.0 ± 1.3, 1.3 ± 0.5 and 0.25 ± 0.17 Gy for photon FinF with FB, with BH, and proton PBS, respectively (p*<0.001).

Conclusion

For left‐sided whole breast treatment with the photon FinF technique, patients with large breast volumes (> 1000 cc) are more likely to receive higher heart doses than patients with smaller breast volumes. FinF with BH or proton PBS can significantly lower heart doses. For proton treatment, the heart doses were minimal and patients’ breast volumes were not correlated with heart doses.

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Plan Scoring Metric Using Only DVH Information for Evaluation and Comparison of IMRT Treatment Plans

J Giltz^1,*, W Weaver², M DeWeese³

(1) University of Kentucky, Lexington, KY, (2) Alyzen Medical Physics, Jonesboro, AR, (3) Alyzen Medical Physics, Paragould, AR

Purpose

To develop a meaningful metric which can be used to evaluate the quality of IMRT treatment plans (both absolutely and comparatively) using only information from a dose volume histogram.

Methods

Beginning with a simple linear/non linear piecewise function, equations were iteratively developed that were able to significantly differ in value based on a clinical priority, while maintaining a structure in which minor penalty is associated under a threshold, and then a non‐linear section which approaches a power function with further deviation from the goal. It was determined additional evaluation structures were needed to give the DVH sufficient information for evaluation, as there are other factors besides organ at risk doses to consider. The equation was designed such that a score of 100 or greater would represent a failing plan.

Results

With judicious application of constants and careful consideration of typical clinical evaluation, the metric developed is capable of roughly approximating the evaluations that would be made by a clinician when reviewing an IMRT plan. More significantly, when comparing competing plans, it can produce a quantitative comparison between the plans to aid in clinical decisions. On final development for this report, penalty values between 0 and 2 represent a well constructed plan, between 2 and 20 are acceptable though non ideal, between 20 and 100 are not meeting (but potentially clinically acceptable).

Conclusion

A meaningful metric can be made using only information retrievable from a DVH. It does require creation of at least one non‐traditional structure. The specific metric developed in this investigation still has room for refinement, however, it is a reasonably simple set of equations that can be implemented clinically without significant trouble to generate several advantages in IMRT plan design and evaluation.

Alyzen Medical Physics is the employer of all three authors, James Giltz being an affiliate resident through University of Kentucky. Alyzen has direct interest in integrating this metric into proprietary software.

PO‐BPC‐Foyer‐32

Evaluation of a Hybrid Verification Technique for Pre‐Treatment QA of Single Isocenter Multi‐Metastatic SRS Treatments

S Ahmed^1,*, J Kapatoes², G Zhang³, E Moros⁴, V Feygelman⁵

(1) H Lee Moffit Cancer Center and Research Insitution, Tampa, FL, (2) Sun Nuclear Corporation, Melbourne, FL, (3) H. Lee Moffitt Cancer Center, Tampa, FL, (4) H. Lee Moffitt Cancer Center, Tampa, FL, (5) H. Lee Moffitt Cancer Center, Tampa, FL

Purpose

Single‐isocenter stereotactic radiosurgery (SRS) technique for multiple brain metastases is gaining popularity due to its efficiency. It is prudent to apply the IMRT‐style pre‐treatment dosimetric QA to all of these complex plans. The challenge is the small targets with sometimes substantial distance between them. This study is aimed to validate a commercial hybrid measurement/calculation EPID — based system (PerFraction from Sun Nuclear Corp.) for dose verification of single‐isocenter treatments.

Methods

The system combines MLC apertures captured by an EPID with all other time‐resolved accelerator parameters extracted from the log files. The fluence is fed into a GPU‐based superposition algorithm for dose calculation on a patient CT. Three SRS plans contained 3 to 5 targets ranging from 0.75 to 3.6 cm in diameter. The non‐coplanar VMAT plans were optimized using a standard SRS protocol on a cylindrical PMMA phantom with a film insert, and delivered on a Varaian TrueBeam accelerator equipped with a standard Millennium 120‐leaf MLC. The phantom was aligned by CBCT and at least two planes per plan were measured using calibrated EBT‐XD radiochromic films. Film measurements were scaled to absolute dose using the ion chamber measurement in one of the PTVs strategically placed at the center of the phantom. The films were processed in RIT113 v 6.6 software and digital γ analysis was performed with 3%/1 mm and 2%/2 mm criteria (global normalization and 10% of max low‐dose cutoff), and filter level 3.

Results

The PerFraction calculations were in good agreement with the film measurements. The average γ‐analysis passing rates were 97.45% ± 4.28% and 96.67% ± 4.29% for 3%/1 mm and 2%/2 mm, respectively. Equally importantly, the distance to agreement between the planned and reconstructed dose profiles in the target regions was sub‐millimeter.

Conclusion

PerFraction is a feasible instrument for the pre‐treatment QA of single isocenter multi‐metastasis SRS treatments.

The work was supported in part by a grant from Sun Nuclear Corporation. SA is a graduate student, JK is an employee at SNC and VF is the PI. GZ and EM has no disclosure and conflict of interest.

PO‐BPC‐Foyer‐33

A Novel Quality Assurance (QA) Phantom for Verification of Accuracy of Six Degrees of Freedom (6DOF) Couch in Both Varian and Elekta Platforms

M Weber^1,*, S Varadhan², D Kristupaitis³, C Johnson⁴

(1) Methodist Hospital, St. Louis Park, MN, (2) Edina High School, Edina, MN, (3) Minneapolis Radiation Oncology, Minneapolis, MN, (4) Radiation Therapy at Fairview Southdale, Edina, MN

Purpose

To assess the accuracy of 6 Degrees of Freedom (6DOF) couch for patient positioning in bothVarian and Elekta platforms using a custom developed phantom that can be used for daily quality assurance.

Methods

An 80 mm acrylic cube with implanted titanium markers at known off set distances and eight aluminum wire markers 2 mm × 10 mm in diameter set in two rows that project on CBCT slices was used in this study. The cube was mounted on a novel platform that was precisely milled using a computerized numerical control (CNC) milling machine so that the cube is warped 2.5 degrees in each of the rotational axis (Pitch, Roll and Yaw). CBCT images were acquired in both Varian True Beam and Elekta Versa linacs and analyzed using the vendor supplied software. The 6DOF couch was adjusted based on the alignment of markers and aluminum wires embedded in the acrylic cube.

Results

The baseline tilt accuracy of the CT and Linear accelerator couch was verified using a digital level and dual axis protractor. With the phantom precisely mounted on the platform with known rotational offsets, translational and rotational measurements were performed with a Perfect Pitch (Varian) and Hexapod (Elekta). We achieved an alignment accuracy of 0.2 mm and 0.2 degree on both platforms.

Conclusion

We have validated a custom developed phantom that can be used for quick and robust daily QA of 6DOF couches to ensure accurate patient positioning in highly conformal treatments. The current QA device can test the performance of the 6DOF couch on a True Beam (version 2.0) and Elekta Hexapod couches with an alignment accuracy of 0.2 mm and 0.2 degree. This phantom has been integrated as part of daily QA on our Linear accelerators.

PO‐BPC‐Foyer‐34

Applicator Displacements Study For Endometrial Cancer Treatment With The Fractionated High‐Dose Rate GYN Brachytherapy

M Shojaei^*, M Rahman, S Pella, G Kalantzis

(1) Florida Atlantic University, Boca Raton, Florida

Purpose

This retrospective study evaluates and analyzes the applicator displacements, for endometrial cancer treatment with the fractionated high‐dose‐rate brachytherapy, in coordinate system for the initial fraction in comparison with subsequent fractions over the entire multi fractionated treatment.

Methods

A retrospective analysis of 118 intracavitary high‐dose‐rate brachytherapy treatment plans of 30 cervical cancer patients that were generated in the treatment planning system Oncentra, and imported in Eclipse for registration of the subsequent treatment plans into the initial CT‐image guided plan and then analyzing the applicator displacements. A MATLAB based rigid registration method for 3D point‐clouds was employed to determine rotation and translation of the implanted applicator precisely.

Results

The applicator rotations about Y and Z axis for the first fraction is compared with other fractions for each patient and then reported. In addition, the applicator translation is successfully calculated and found zero for all patients.

Conclusion

We evaluated the displacement of the cylinder for each fraction compared to the initial plan based on a 3D point‐cloud rigid registration. According to this study, no significant displacement variations were found between each fraction. However, Immobilization devices need improvement in order to minimizing any applicator displacement and also to prevent any displacement during transportation and treatment delivery.

PO‐BPC‐Foyer‐35

Dose Blurring of Three Types of Left‐Sided Breast Cancer Plans Due to the Setup Error: 3D‐CRT, FIMRT, and VMAT

T Hwang^*, T Koo

(1) Hallym University Medical Center, Chuncheon‐si, Gangwon‐do

Purpose

This study compared the dose blurring of three types of radiotherapy plans due to the setup error for the left‐sided breast cancer; 3D conformal radiotherapy (3D‐CRT), forward intensity‐modulated radiotherapy (FIMRT), and volumetric modulated arc therapy (VMAT).

Methods

Four patients with left‐sided breast cancer with breast conserving surgery were chosen. The prescription dose was 50.4 Gy in 28 fractions. The target volume was limited with the clinical target volume (622.46 ± 200.75 cm3). For 3D‐CRT, conventional tangential fields using dynamic wedges between 15° and 20° were used. For FIMRT, multi‐leaf collimators (MLCs) were used instead of the wedges under the same gantry angle in the 3D‐CRT. For VMAT, two fields (clockwise and counterclockwise) were used with the similar tangential fields. Skin flash technique was not adopted with VMAT. The plans with setup error, where iso‐center was shifted by ±3 mm along the x or y‐axis in the beam's eye view, were obtained from each optimized plan with the same monitor units (MUs). We compared homogeneous index (HI), D2 (the dose received by the 2% of the target volume), and conformity index (CI) for the target coverage, and compared mean doses to ipsilateral lung, contralateral lung, heart, and LAD coronary artery.

Results

While HI, D2, and CI of VMAT were significantly better than both those of 3D‐CRT and those of FIMRT, the variations of HI, D2, and CI of VMAT were much larger than others. However, blurred target doses for VMAT were still better than others, and mean doses to normal organ for VMAT were also not affected with comparison to those for other techniques.

Conclusion

For radiotherapy plans for the left‐sided breast cancer VMAT is not only the most useful technique for the target coverage, but also the most reliable for the setup error. More patients will be analyzed in the upcoming poster presentation.

This work was supported by Radiation Technology R&D program through the National Research Foundation of Korea funded by the Ministry of Science, ICT & Future Planning (No. 2013M2A2A7038291)

PO‐BPC‐Foyer‐36

Hybrid Magnetic Resonance/Computed Tomography Compatible Phantom for Magnetic Resonance Guided Radiotherapy

M Kim^1,2,*, S Ahn¹, S Lee², T Suh²

(1) Department of Radiation Oncology, Yonsei Cancer Center, Yonsei University College of Medicine, Yonsei University Health System, Seoul, Korea, (2) Department of Biomedical Engineering, The Catholic University of Korea College of Medicine, Seoul, Korea

Purpose

Development of hybrid MR/CT compatible phantom and tissue‐equivalent materials on each MR and CT image was purposed.

Methods

To accomplish our purpose, we designed the essential requirements and developed the hybrid MR/CT compatible phantom in this study. Total 12 different tissue‐equivalent materials both for each MR and CT image was developed using various chemical component. The uniformity of each sample was calculated. The developed phantom was designed to equip 14 plugs which contained various tissue equivalent materials. Measurement using the developed phantom were done using 3.0‐T scanner with 32‐channel and Somatom Sensation 64. For MR image, T1 and T2 measurement was performed. The HU on CT depending on the amount of K₂CO₃ which was applied in tissue‐equivalent materials to modulate HU on CT and its fitted curve are conducted.

Results

The maximum percentage difference of HU value on CT image by adding K₂2CO₃3 was 3.31%. Also, the uniformity of each tissue was evaluated by calculating %PIU of MR image, which was 82.18% ± 1.87 with 83% of the acceptance value and the average of circular‐shaped ROIs on CT image for all sample was within ±5 HU. The T1‐T2 measurement data were compared with reference data and the average of percentage difference was 2.86% and −13.37% for T1‐ and T2 relaxation time, respectively. With the 5% of tolerance for percentage difference, 10 measurement data among 24 was acceptable and tissue‐equivalent materials of liver was acceptable as tissue‐equivalent materials.

Conclusion

A hybrid MR/CT compatible phantom for image acquisition of MR and CT was designed and investigated the relation between MR and CT image for MR‐only based radiotherapy in terms of target delineation and radiation dose calculation. In addition, various tissue‐equivalent materials for both MR and CT image to be inserted into the developed phantom were described in this study.

PO‐BPC‐Foyer‐37

Instability of OSMS Camera Caused by HVAC Vent

B Rice^*, C Bass

(1) Associates In Medical Physics, Richmond, VA

Purpose

The purpose of this study was to investigate the effects of an HVAC unit on the thermal drift of our Optical Surface Monitoring System (OSMS).

Methods

An HVAC vent is situated behind the central OSMS camera. The OSMS was allowed to reach thermal equilibrium with the HVAC unit powered off before acquiring measurements. A reference image of an anthropomorphic phantom was then captured at time zero. OSMS reported phantom displacements from reference conditions and camera reported temperatures were recorded at 2–5 min intervals while the HVAC system was manually cycled on, off, and back on again. Measurements were continued after installing an air deflector to direct airflow away from the OSMS camera with the ventilation system on.

Results

During HVAC operation OSMS falsely reported phantom 3D displacements from baseline of 0.6 mm–0.7 mm. The majority of the displacement (0.5 mm–0.6 mm) occurred over the first 4 min of HVAC operation, with stabilization occurring after 8 min. The return to baseline occurred more gradually, with a total time to stabilization of eighteen minutes after powering off the HVAC. The longitudinal and vertical displacements ranged from 0.40 mm–0.50 mm and 0.35 mm – 0.70 mm, respectively, with the HVAC on. The lateral displacement ranged between 0.00 mm – 0.05 mm. All temperature readings reported by the central camera indicated a decrease in temperature after the HVAC was turned on, and correlated well with the OSMS displacements. Installing an air deflector resulted in the total displacement decreasing from 0.6 mm to 0.3 mm.

Conclusion

Variations in temperature affect the OSMS stability. HVAC vent proximity to a camera exacerbates the thermal drift that is seen under normal conditions and could lead to false positive shifts during stereotactic treatments.

PO‐BPC‐Foyer‐38

Utilization of Radimetrics to Calculate Peak Skin Dose for Fluoroscopically Guided Interventions: A Guide for Three Manufacturers

N Ball^1,*, Z Glass², R Neill¹, J Nye¹

(1) Emory University, Atlanta, GA, (2) Alliance Medical Physics, LLC., Alpharetta, GA

Purpose

Peak skin dose (PSD) estimates are an important dose metric to assess if, when, and how to follow‐up with patients who undergo fluoroscopic guided procedures. Radimetrics (Bayer Healthcare LLC, Whippany, NJ) is a commercially‐available dose tracking tool that can help gather data for PSD estimations. In this study, we share our recent experiences converting reference point air kerma (K_(a,r)) values to PSD estimates using data available through Radimetrics.

Methods

Our healthcare system has three vendors that are configured to export radiation dose structured reports (RDSR), or dose sheets and DICOM images to Radimetrics. A custom excel tool was developed to estimate PSD values based on corrections made to K_(a,r) measurements, including inverse square correction, f‐factor, backscatter, and table attenuation. The required data for such a calculation (field size, table height, beam filtration, angulation data) were extracted from Radimetrics in a vendor‐specific fashion, and used as input variables within our in‐house PSD estimation calculator.

Results

A majority of required input data are easily exported using the “Study Exporter” tool in Radimetrics; however, this export tool is missing key information required of robust PSD calculations. All data for GE, barring beam filtration, can be found in this export. Philips requires further data from the RDSR to determine table height and beam filtration. Siemens machines require additional information located within DICOM meta‐data to determine table height, beam filtration, and angulation. Caution is warranted when using table height data from different sources, due to differences in table height field definitions.

Conclusion

Radimetrics can be a useful tool for piecewise PSD estimates; however, there are limitations and vendor‐specific intricacies. Easily locating the variables needed to adjust for acquisition setup and technique is often non‐trivial, and therefore the development of vendor‐specific implementation techniques is essential for PSD calculations.

PO‐BPC‐Foyer‐39

Variation in Fluoroscopy Technique& Exposure Rate for Different Phantoms for Dose Estimation Program

V Garcia^*, W Wang

(1) University of Oklahoma Health Science Center, Oklahoma City, OK

Purpose

Fluoroscopy can be very beneficial, but not without the possibility of high dose to the patient from prolonged fluoroscopy. The dose is determined indirectly by the Automatic Brightness Control (ABC), which chooses the kVp and mA to maintain image quality. These parameters will change based on the patient thickness. It is important to check these and the exposure rate to determine how much dose the patient will receive from an examination.

Methods

Using GE 9900 and Philips BV Pulsera C‐Arms, a RadCal 10X5‐6 ion‐chamber was placed at 70 cm source‐to‐chamber distance. An Acrylic phantom was placed on the image intensifier, ranging from thicknesses of 1 inch to 12 inches. For each thickness of Acrylic, the kVp and mA chosen by the ABC and the exposure rate measured by the ion‐chamber. The kVp, mA, and exposure rate were recorded for various types of fluoroscopy examinations (e.g., Thorax, Abdominal, etc.), Standard and High‐Level fluoroscopy, and for the various magnification modes. The techniques were compared with those using Copper and various Nuclear‐Associates phantoms.

Results

The ABC adjusts the kVp and mA in a linear fashion until the mA saturates and only the kVp increases, as the thickness of the Acrylic increases. As the magnification increased, the kVp and mA increased at a much faster rate than the lower magnifications. The exposure rate increased exponentially with the increased thickness of Acrylic. The thickness of Copper was compared to the thickness of acrylic resulting in the same exposure rate (i.e., 2 mm Cu is equivalent to 6.2 in. of acrylic).

Conclusion

From the exposure rate and fluoroscopy time, patient dose can be estimated for different thicknesses of patient, exam types, and magnification modes. The dose estimation program can use the techniques to assess the skin and organ dose.

PO‐BPC‐Foyer‐40

Mapping Force‐Equivalent Vector Fields Using the Maxwell Stress Tensor

A Shutler^*, I Rutel

(1) University of Oklahoma Health Science Center, Oklahoma City, OK

Purpose

Mapping the magnetic force‐equivalent vector field from measurements made in a 3D space using a gaussmeter. This method can be implemented for use in delivery of superparamagnetic iron oxide nanoparticles (SPION), providing precision targeting of nanomedicine; as well as potential secondary applications in mapping force field lines in MRI rooms.

Methods

We demonstrate computation of the force equivalent vector field by applying a simplified Maxwell stress tensor to a 3D magnetic field space (setting electric fields to zero). From the generalized force equation of a purely magnetic field, we apply the tensor and compute the forward derivative to arrive at the equivalent force. We use a next‐next nearest neighbor (NNNN) method to compute the gradient from one point in space to its 8 N‐N nearest neighbors. This method increases computational efficiency and allows multidirectional computation of the derivative by comparing the change in magnetic field across all directions. Demonstration of the method is performed by constructing a simulated magnetic field in a 3D space and applying the calculations to the sample field.

Results

For a sample 5 × 5 × 5 magnetic field that grows isotropically, the eight NNNN force equivalent field is found and plotted with magnitude and direction. The calculation produced appropriate results with equivalent force vectors increasing in directions with increasing gradients.

Conclusion

This work provides the underlying work for computing force fields in any space, where the step size between measurements is known, and can be generalized to any arbitrary time‐invariant electromagnetic fields. While the work here demonstrates this method applied to a full 3D field, the input fields can be 1D or 2D, and the outputs can be manipulated to show field planes along the full 3D space.

PO‐BPC‐Foyer‐41

Fabrication of Photon and Electron Bolus Using 3D Printing Technology

F Li^*, J Jung, S Lebron, J Park, G Yan, J Li, C Liu, B Lu

(1) University of Florida, Gainesville, FL

Purpose

To fabricate patient specific bolus for photon and electron treatment using 3D scanning and 3D printing.

Methods

The surface geometry of the patient treatment area is acquired using 3D SYSTEMS Sense Handheld 3D Scanner, which is then digitized and modeled in Rhinoceros 5 CAD software. We tested two ways to fabricate a custom bolus: casting and direct printing. (1) For casting, a 3D model of the mold is designed in Rhinoceros 5, and 3D printed using PLA filament with 10% infill density. The resulting mold is then used to make a silicone bolus casting using SMOOTH‐ON PMC‐780 industrial liquid rubber compound. (2) For direct printing, a 3D model of the bolus is designed in Rhinoceros 5 and directly printed using PLA filament with 100% infill density. The Mold and bolus are printed using Fusion3 F400‐S 3D printer.

Results

Both methods produce bolus with clinically acceptable densities and fit the patient surface. The silicone bolus made by casting method is soft and more comfortable for the patient but required 4 days to prepare (1 day to design and print, 3 days to solidify the casting material). The direct printing method, on the other hand, requires only 1 day to prepare but is less comfortable.

Conclusion

We have demonstrated the applicability of bolus fabrication using 3D printing technology. The direct printing method has been successfully implemented clinically at University of Florida cancer center for electron radiation therapy.

PO‐BPC‐Foyer‐42

A Prospective Study of the Impact of PTV Margin Reduction for Patients with Localized Prostate Cancer: Delivered Dose and Quality of Life

A Kumarasiri^*, C Liu, S Brown, C Glide‐Hurst, M Elshaikh, B Movsas, I Chetty

(1) Henry Ford Health System, Detroit, MI

Purpose

To determine the impact of reducing PTV margin on patient reported quality‐of‐life (QOL) for patients with low or low‐intermediate risk prostate cancer with consideration of the actual delivered dose computed using deformable dose accumulation (DDA).

Methods

The IRB‐approved prospective study included 20 patients; nine planned using reduced margins (5 mm uniform with 4 mm at prostate/rectum interface), and 11 control patients planned using standard margins (10/6 mm). “Dose‐of‐the‐day” was calculated using DDA, in which the daily CBCT dataset was deformed to the planning CT (PCT), and dose was computed on the resampled PCT using a parameter‐optimized, B‐spline algorithm (Elastix, ITK/VTK). Dose mapping was performed using the energy‐mass congruence method. QOL data were collected via Expanded Prostate cancer Index Composite (EPIC‐26) questionnaires pre‐ and post‐treatment, and at 2,6,12,18,24,36 month time points. QOL data were standardized [range:0–100] and baseline‐corrected. Mean differences between the margin‐reduced group and control group (QOL_MR‐QOL_control) were calculated. Bladder/PTV overlap and rectum/PTV overlap were dosimetrically assessed to evaluate OAR high dose regions.

Results

Differences between the delivered (cumulative, DDA‐based) mean dose and planned mean dose were less than 2.2 Gy for targets and all OARs for both groups, and were not statistically significant (P = 0.1). Standardized and baseline‐corrected mean QOL_MR‐QOL_control for EPIC domains categorized as “Urinary Incontinence”, “Urinary Irritative/Obstructive”, “Bowel”, “Sexual”, and “Hormonal” were 2.2, 12.5, 10.4, 13.5, and −1.1 at 36 months after radiation therapy (higher values better). The control group showed larger PTV/rectum and PTV/bladder intersection volumes (7.2 ± 5.8, 18.2 ± 8.1 cc) than the margin‐reduced group (2.6 ± 1.8, 12.5 ± 8.3 cc), while the dose to these intersection volumes were not statistically different (P > 0.1) between groups. PTV/rectum intersection volume correlated moderately (R = −0.5) with “Bowel” EPIC domain.

Conclusion

Margin‐reduced prostate treatment exhibited clinically meaningful improvement of QOL without compromising the target dose coverage. Confirmation with more patients and longer follow‐up is warranted.

This work was supported in part by a research grant from Varian Medical Systems, Palo Alto, CA

PO‐BPC‐Foyer‐43

Clinical QA of the D2SRS Micro‐MLC Attachment

C Kabat^1,*, H Parenica¹, Y Liu², H Wen², E Pappas³, N Papanikolaou¹, S Stathakis¹

(1) University of Texas Health Science Center San Antonio, Texas, (2) Linatech, Sunnyvale, California, (3) Technological Educational Institute of Athens, Greece

Purpose

Stereotactic radiosurgery requires thorough review and evaluation of equipment before being clinically accepted for patient treatment. Linatech's micro‐MLC attachment allows for superior treatment by coupling 102 2 mm thick leaves at isocenter, ten cones varying in size, and a positional dual camera all into one attachment. To ensure TG‐54 requirements for stereotactic radiosurgery, Linatech's micro‐MLC attachment underwent an extensive evaluation to obtain clinically relevant information and develop QA practices that effectively evaluate alignment.

Methods

Beam profiles were measured for square field sizes 0.7 cm through 12 cm with depths ranging from 1.5 to 20 cm. All field sizes were measured with: TN60012 micro‐diode, 0.0016 cc pinpoint, and 0.004 mm diamond chamber for 6 MV. MLC positional accuracy was assessed with both picket fence and inverse picket fence tests. A Winston Lutz test in combination with a star pattern were created for reviewing tolerance during micro‐MLC attachment and cone alignment at collimator angles 60, 120, 180, 240, 270, and 300 with gantry angles of 0, 90, 180, and 270. Patient plans were delivered and verified using PTW's Octavius phantom and VeriSoft using a 3% and 3 mm 3D gamma analysis with no optimization shifts. A six met plan was developed and delivered using SRS procedures to a 3D printed RTSafe gel phantom for final verification.

Results

MLC leakage was determined to be 1.6% and the penumbra was reduced by 2.67 mm for a 6 × 6 cm field with the attachment. Reattachment of the assembly demonstrated a tolerance of 0.23 ± 0.22 mm, leaves were found to be within a 0.1 mm. Cone bank A was found to have a tolerance of 0.21 ± 0.07 mm while bank B had 0.35 ± 0.09 mm Three patient plans verified using PTW's VeriSoft obtained gamma values of 96.8%, 97.1%, and 93.0%.

Conclusion

The D2SRS micro‐MLC attachment has fallen within expected specifications and the RTSafe has provided verification of the systems abilities for stereotactic radiosurgery.

Supported in part by CPRIT Training Grant (RP170345); Equipment tested was provided by the company Linatech

PO‐BPC‐Foyer‐44

Annealing and Decay Characteristics of OSLDs

B Owen^*, S Mahendra, W Jackson

(1) Northwest Medical Physics Center, Lynnwood, WA

Purpose

The purpose of this work is to characterize annealing and decay characteristics of OSLD's using the NMPC annealer and ambient clinical light. This required commissioning a new MicroSTAR ii system.

Methods

To commission the MicroSTAR ii system, calibration OSLD's spanning the whole clinical range were irradiated, and QC OSLD's for a subset were also irradiated. Calibration files were verified by reading the dose of QC OSLD's. To test decay by annealing, OSLD's with various residual doses were initially read with the MicroSTAR ii reader prior to annealing. The active portions of multiple OSLD's were exposed and placed into the annealer, and the dose was read periodically. The NMPC annealer has an aluminum case and uses blue LED's to anneal the OSLD's. To test decay by ambient clinic light, six OSLD's were also left in different places with different amounts of ambient clinic light to characterize the decay that took place.

Results

With the annealer, OSLD's with more dose required more annealing time to reach a background dose of 0.1 cGy. The dose on OSLD's with their active portions open to the light decayed faster than those that had less ambient light exposure.

Conclusion:

Our recommendation is that OSLD's below 200 cGy need to be annealed for 45 min, between 200 cGy and 500 cGy they need to be annealed 60 min, and between 500 cGy and 1000 cGy they need to be annealed 90 min. Also, it is important not to leave OSLD's with their active portion left open to the light.

PO‐BPC‐Foyer‐45

Dosimetric Comparison Between IMAT and IMRT for Different Planning Target Volume of Esophageal Cancer

R Zhang¹, Y Gao², w bai^1,*, Q Zhang¹, R Li¹, M Miao¹

(1) The Fourth Hospital of Hebei Medical University, Shijiazhuang, Hebei, (2) Hebei General Hospital, Shijiazhuang, Hebei

Purpose

To compare the dosimetric differences between Intensity modulated arc therapy (IMAT) and static intensity modulated radiotherapy (IMRT) for different PTV volume of esophageal cancer(EC).

Methods

Fourty patients who were diagnosed with thoracic EC. Including 10 cases located in the upper, middle, and the lower thorax, respectively. IMAT and IMRT two plans were generated with The Elekta Oncentra4.1 Planning System in Varian 23EX Linac, prescription dose of 60 Gy in 30 fractions to the PTV. All treatment plans of the 40 cases were evaluated using the dose‐volume histogram parameters of PTV and the organs at risk. The monitor units (MUs) were also examined.

Results

For PTV volume<50 cm3 group (PTVs), IMAT plan had superior homogeneity when compared with IMRT plan, while the lung V5 and MLD were slightly higher for IMAT plan. For50 ˜150 cm3 group(PTVm), PTV D95 for VMAT got closer to prescription dose, IMAT plan resulted in a slightly lower lung V10 and higher lung V30. However, IMAT plan had lower V100 in the PTV, compared to IMRT plan for PTV volume >150 cm 3 group (PTVb), and sparing of lungs showed no statistically significant differences between the two techniques. When compared with IMRT plan, IMAT plan reduced the monitor units by an average of 15% and 25% in the PTVm group and PTVb group. However, IMAT plan provided an average of 13.5% more monitor units than IMRT plan in the PTVs group.

Conclusion

For PTVs IMAT is better than IMRT, not only in the treatment time but also in the PTV dose,is the first choice. In addition. IMAT plan provides equivalent conformal dose coverage and sparing of OARs for the PTVm EC with less delivery time. However, IMRT is the first choice for a PTVb EC, since IMAT plan with worse target volume coverage and even increases the spring of OARs.

PO‐BPC‐Foyer‐46

Use of 4DCT Scans to Create Improved Custom Cardiac Blocks for Left Sided Breast Cancer Treatments

P Dupre^1,*, C Fitzherbert², C Hand², L Solin²

(1) University of Pennsylvania, Philadelphia, PA, (2) Albert Einstein Medical Center, Philadelphia, PA

Purpose

For patients receiving treatment for left breast cancer, cardiac toxicity increases with increased radiation dose to the heart. Furthermore, the accurate heart dose is unknown when its intrinsic (breathing and cardiac cycle) motion is unaccounted for. Current clinical techniques (e.g., deep inspiration breath hold and prone treatment) are not feasible for all patients. A new method was developed utilizing 4DCT scans to improve custom cardiac blocks to minimize heart dose.

Methods

4DCT scans were acquired and a maximum intensity pixel (MIP) heart was contoured for twenty patients. Custom heart blocks were created to fully block the MIP heart volume. A heart block based on the standard 3DCT image was retrospectively created. The difference in heart block leaf parameters was compared. Differences in MLC leaf positions, heart block area, and dose statistics were analyzed.

Results

In all 20 cases, the heart block created using the 4D scan had a larger area than the corresponding 3D block. The mean increase in MLC leaf coverage was 3.9 mm (0.5 mm–20.1 mm). The mean increase in area of the heart block was 2.6 cm² (0.27–6.65 cm²). The increase in MIP heart volume from the dose volume histogram (DVH) from the patient plans showed that the average of the mean dose for MIP heart versus 3D heart volumes was larger by 17.8 cGy (0.02–70.3 cGy).

Conclusion

4D heart volume and blocks accounting for intrinsic respiratory motion and cardiac motion are greater in size than 3D heart volume and blocks. These larger blocks result from the larger contour created from the MIP image. This technique for improving custom heart blocks requires no special patient techniques and can be implemented easily with 4DCT capabilities. The larger mean doses found for the MIP heart account for a more accurate heart dose representation and would be even greater if adequate blocking was not used.

PO‐BPC‐Foyer‐47

VMAT Optimization and Dose Calculation in the Presence of Metallic Hip Prostheses

H Parenica^1,*, R George¹, P Mavroidis², Z Shi¹, Y Li¹, W Jones³, C Ha¹, N Papanikolaou¹, S Stathakis¹

(1) UT Health San Antonio Cancer Center, San Antonio, TX, (2) University North Carolina, Chapel Hill, NC, (3) South Texas Veterans Health Care System, San Antonio, TX

Purpose

To quantitate and compare the effect of hip prostheses on dose distributions calculated using Collapsed Cone Convolution Superposition (CCCS) and Monte Carlo (MC) (with and without correcting for the density of the implant and surrounding tissues). The use of full VMAT arcs versus VMAT arcs avoiding the hip implants (i.e., skip arcs) was also studied.

Methods

Six prostate patients with hip prostheses were studied. All were prescribed a dose of 7800 cGy over 39 fractions. The hip prostheses and the streaking artifacts on the CT images were contoured by a single physician. Two plans were created in the Pinnacle³ TPS: one using full VMAT arcs and one using VMAT arcs that avoided going through the prostheses. From both of those plans, copies were made and the doses were recalculated with the densities of the prostheses and surrounding tissues overridden (5 g/cc and 1 g/cc, respectively). The plans were then exported to the Monaco TPS and recalculated using a Monte Carlo dose calculation algorithm. The changes in dose to PTVs and surrounding Organs at Risk (OAR) were evaluated in VelocityAI.

Results

Plans calculated with CCCS with correct density information showed reasonable agreement with MC calculations. Doses to OAR were significantly decreased when full arc VMAT plans were used instead of skip arc VMAT plans. For full arc plans, there was some difference in Pinnacle³ when plans were recalculated using correct density information. Plans in Pinnacle3 showed good agreement with Monaco when correct density information was used.

Conclusion

When planning for prostate patients with hip prostheses, correct density information for implants and surrounding tissues should be used to optimize the plan and ensure optimal accuracy. Full arcs could be used to spare dose to OAR, while maintaining adequate PTV coverage, when using a model‐based or MC dose calculation.

PO‐BPC‐Foyer‐48

Investigation of 3D Gamma Analysis for Clinical SRS Treatments

Y Wang^1,*, C Velten², P Black³, J Adamovics⁴, C Wuu⁵

(1) Department of Radiation Oncology, Columbia University, New York, NY, (2) Department of Applied Physics and Applied Mathematics, Columbia University, New York City, NY, (3) Department of Radiation Oncology, Columbia University, New York, NY, (4) Department of Chemistry, Biochemistry and Physics, Rider University, Lawrenceville, NJ, (5) Department of Radiation Oncology, Columbia University, New York, NY

Purpose

Stereotactic Radiosurgery (SRS) utilizes precise patient positioning and a higher single radiation dose fraction delivered to a focused area. However, due to highly irregular treatment fields with steep dose gradients, it is challenging to perform patient specific quality assurance (PSQA) using conventional methods, for example, using two‐dimensional (2D) diode arrays. EBT3 films with submillimeter resolution have been used to resolve this problem. To increase confidence in SRS plans, it is important to evaluate dose difference in 3D. In this study, the PRESAGE 3D dosimeter was used to conduct PSQA of a SRS plan to treat a spinal metastasis with field sizes as small as 1.5 1.5 cm2.

Methods

This work consists of four major components, (1) Simulation: CT images of a 3D dosimeter with metal ball bearings were acquired using a Siemens Somatom CT scanner and imported into Varian Eclipse for verification plan generation. (2) Irradiation: The verification plan was delivered on a Varian TrueBeam linear accelerator to the dosimeter. (3) Dose reconstruction: The irradiated dosimeter was scanned using a parallel beam optical scanner with submillimeter resolution and images were reconstructed using filtered back‐projection. (4) Analysis: 3D gamma analysis was performed and a 3D view of planned and measured dose distributions with failed dose points marked was created using MATLAB.

Results

The passing rates of 3D gamma comparison are 97.1% and 85.4% with criteria of 3%, 3 mm and 2%, 2 mm, respectively. Comparison of the reconstructed 2D image at the isocenter with the planned dose using DoseLab yielded a passing rate of 98.4% with 2%, 2 mm criteria. 3D visualization of failed dose points relative to organs at risk can be clinically used to inform the decision to accept a plan.

Conclusion

This study demonstrates the capabilities of the PRESAGE 3D dosimeter for PSQA of clinical SRS plans.

PO‐BPC‐Foyer‐49

Evaluation of Quad Wedge and IC‐Profiler to Calculate R50 for Non‐Standard Electron Energies

J Sick^*, D Perrin, J Fontenot

(1) Mary Bird Perkins Cancer Center, Baton Rouge, LA

Purpose

To develop a procedure to efficiently measure electron R₅₀ utilizing the Sun Nuclear IC‐Profiler Quad Wedge accessory for non‐standard energies. Currently, methods to calculate R₅₀ are only provided for energies 6, 9, 12, 15, 16, 20, and 22 MeV.

Methods

The energies investigated have been turned off the standard settings to achieve specified R₉₀ values. PDDs were measured using a water tank for nominal electron energies of 7, 9, 10, 11, 13, 16, and 20 MeV with 1, 2, 3, 4, and 5 mm of PVC placed in a 25 × 25 cm² cone as close to the linear accelerator head as possible. R₅₀ values were calculated for overlapping energies (9, 16, 20 MeV) and compared to water tank scans. Plots of the water tank measured R₅₀ versus the AreaRatio (a metric used by Sun Nuclear) for each energy were fitted with a quadratic. R² values were used to determine the accuracy of the fitted regression. Last, IC‐Profiler calculated R₅₀ values were compared to solid water spot measurements.

Results

The average distance‐to‐agreement for 9, 16, and 20 MeV using the coefficients provided by Sun Nuclear was −0.17 ± 0.83 mm. Quadratic fits using the PVC range shifters yielded the following R² values: 7 MeV = 0.8408, 9 MeV = 0.9143, 10 MeV = 0.9987, 11 MeV = 0.9954, 13 MeV = 0.9988, 16 MeV = 0.9515 and 20 MeV = 0.8898. The average DTA for these energies calculated by the IC‐Profiler was 0.02 ± 0.43 mm versus 0.96 ± 0.48 mm for solid water spot measurements.

Conclusion

All of the measurements suggest the sensitivity of the IC‐Profiler Quad Wedge is capable of meeting the 2%/2 mm tolerance suggested by TG‐142. Although still much improved from solid water spot check measurements, the uncertainty using PVC sheets (0.43 mm on 1 machine) to shift R₅₀ was higher than that reported by Sun Nuclear (0.18 mm on 11 machines) who changed the bending magnet current. A comprehensive analysis, including multiple matched machines is ongoing.

PO‐BPC‐Foyer‐51

Development of a High Precision Optical System to Assist Radioactive Seed Placement On Eye Plaques

K Nealon^*, A Ayan, J Woollard, N Gupta

(1) Ohio State University, Columbus, OH

Purpose

To develop an optical guidance system which could be clinically implemented to increase the precision of seed placement, and thus limit the dosimetric uncertainty, on customizable I‐125 eye plaques.

Methods

Following a study which demonstrated the substantial impact a slight deviation in seed placement can have on the total dose delivered by an eye plaque, a high precision optical guidance system was developed as an alternative to the purely caliper based seed placement technique which is currently in place at our institution. In this system, the plaque is secured in a fixed location using a stand to ensure that both of the physicist's hands are free to assist with placement. A camera, located above this stand, takes live video of the seed placement and, on a nearby monitor, projects the planned seed location on the plaque. This provides real‐time feedback with sub‐millimeter resolution, to assist with limiting the uncertainty of this process.Once implemented, more consistent and predictable dosimetry should be achievable.

Results

A proof‐of‐concept design has been developed which verified the feasibility of our system. A MATLAB code was written which performs a spatial calibration of an image by relating the number of pixels to the dimensions of a known object. This code allows for measurements to be taken on a snapshot to verify proper calibration. It also projects a grid overlay or the user specified seed geometry on the video feed, allowing for real‐time feedback on the accuracy of seed placement.

Conclusion

This project was based around the practical need to improve upon a system which is currently in use. The proof of concept has been developed, validated and shown to be useful in improving the accuracy of the eye plaque seed positioning process. A higher resolution system is currently in development for full clinical use.

PO‐BPC‐Foyer‐52

Potential Efficacy of Monte Carlo Dose Calculation for 6 MV FFF Beam of M6â„¢ CyberKnife Using BEAMnrc and DOSXYZnrc in EGSnrc Code System

T Neupane^1,*, M Rahman¹, C Shang²

(1) Florida Atlantic University, Boca Raton, FL, (2) Boca Raton Regional Hospital, Boca Raton, FL

Purpose

With the implementation of InCise™ 2 Multileaf Collimator (iMLC) in CyberKnife® M6™ system (M6CK), dose calculations in a heterogeneous media becomes more challenging with a serious of discrete highly intensity‐modulated MLC beamlets and non‐isocentric FFF beam projections. An independent dose prediction model is essential for validating its treatment planning system and dose measurement methodologies. This research is to investigate the efficacy of using BEAMnrc and DOSXYZnrc programs in EGSnrc system for M6CK Monte Carlo (MC) modeling.

Methods

The M6CK Linac head was modeled using BEAMnrc program for millions of particles and stored as phase space files before and after iMLC. These files were then fed into the DOSXYZnrc program for dose calculation. We have already modeled the linac head before MLC using a monoenergetic electron beam as a primary source with Gaussian profile, with energy and FWHM optimized by comparing with measurements, and calculated the dose at 800 mm SAD in a water phantom to verify the model. During MC simulations, various variance reduction techniques were applied as a trade‐off between computation time/simulation histories and statistical uncertainties.

Results

The early results at 10 millions histories showed that the dose distribution for 53.8 mm by 53.9 mm iMLC segment were within an acceptable 2%/2 mm statistical uncertainty. A preliminary model for iMLC module was easily added to linac head module and soon be evaluated.

Conclusion

The current MC model of M6CK using BEAMnrc and DOSXYZnrc programs suggest a promising module‐based approach to establish a full system model (including iMLC), with more flexibility to modify the components/parameters without need of programing expertise, for accurate dose predictions in heterogeneous phantom and multiple measurement detectors.

Professional Symposium – SAM
Marquis Ballroom 5‐8
Medical Physics Leadership Academy

SA‐A‐Ballroom 5‐8‐00

Medical Physics Leadership Academy

Brent ParkerModerator

University Texas Medical Branch of Galveston, Galveston, TX

SA‐A‐Ballroom 5‐8‐01

R. Miller

(1) Northwest Medical Physics Center

Project Management Essentials: Increase Your Impact by Understanding the Bigger Picture — Part 1.

SA‐A‐Ballroom 5‐8‐02

J. Parscale, Perkins Will

Project Management Essentials: Increase Your Impact by Understanding the Bigger Picture — Part 2.

SA‐A‐Ballroom 5‐8‐03

C. Almanza

(1) UT Southwestern Medical Center

Project Management Essentials: Increase Your Impact by Understanding the Bigger Picture — Part 3

SA‐A‐Ballroom 5‐8‐04

A. Pompos

(1) UT Southwestern Medical Center

Project Management Essentials: Increase Your Impact by Understanding the Bigger Picture — Part 4

Medical Physicists are often involved in a project implementation without any formal skills in project management. The project can be the construction of an entirely new department, choosing and implementing a new piece of equipment, a new modality or a new program: all projects share common themes. Physicist involvement level can vary based on both project and work place environment. Further, the success of the project can be impacted based on the roles and responsibilities of others. The purpose of this session is to review some basic tools of project management from a few perspectives based on a case study: a medical physicist, an administrator, and an architect.

Learning Objectives

Understand the role of a medical physicist in project managementExplore some common challenges in project managementReview some tools and resources to enhance the success of a project.

Young Investigator Symposium
Marquis Ballroom 5‐8

SA‐B‐Ballroom 5‐8‐01

Clinical Quality Assurance Applications of a High Spatial Resolution Diode Array for Small Field Dosimetry

M Held^*, A Sudhyadhom

(1) UCSF, San Francisco, CA

Purpose

Stereotactic Radiosurgery (SRS) and Body Radiotherapy (SBRT) commonly utilize small field sizes for radiation delivery, and thus require high spatial resolution quality assurance (QA) devices. Diodes offer high spatial resolution but are also known to exhibit dependencies on field size, beam energy, dose rate, and incident beam angle, reducing dose measurement accuracy. The purpose of this study is to evaluate the dosimetric accuracy of a high spatial resolution diode array.

Methods

A prototype of the SRSMC (SNC, Melbourne, FL) was used to evaluate and quantify its dependencies on field size (5 mm to 80 mm), beam energy (6 MV WFF, 6 MV FFF, and 10 MV FFF), dose rate (repetition rates 100 MU/min to 2400 MU/min), and incident beam angle (0° to 90°). The SRSMC was calibrated on an Elekta VersaHD linac according to the vendor's instructions. Nine clinical VMAT treatment plans with energies of 6 MV, 6 MVFFF, and 10 MVFFF were measured with the SRSMC, for which it was placed inside SNC's StereoPHAN phantom and stereotactically positioned, using the cone‐beam CT on‐board imaging system. The dose distribution was analyzed, using the global gamma index with 3%/1 mm criteria. The absolute dose was evaluated in comparison to the measured dose, using a PinPoint3D (PTW, Freiburg, Germany) ion chamber in a separate plan delivery.

Results

The SRSMC has field size and beam energy dependencies for field sizes <2 × 2 cm². Dose rate dependencies are >1% for dose rates <300 MU/min. Incident beam angle dependence is 2%. The end result of these dependencies on clinical plans is insignificant as measured by patient‐specific QA versus ion chamber dose.

Conclusion

The SRSMC is suitable for small field plan QA with some of the measured effects washing out on clinical plans. Plans with a majority of MUs delivered below 300 MU/min and segment sizes <1 × 1 cm² show larger errors and may require corrections of the diode dependencies.

This work was supported by Sun Nuclear Corporation (SNC).

SA‐B‐Ballroom 5‐8‐02

Linear Accelerator Pulse‐Synchronized Imaging of Scintillator Emission for Patient Surface Dosimetry

I Tendler^1,*, P Bruza¹, J Andreozzi¹, B Williams^2,3, L Jarvis^2,3, D Gladstone^1,2,3, B Pogue^1,2

(1) Thayer School of Engineering, Dartmouth College, Hanover NH, (2) Department of Medicine, Geisel School of Medicine, Dartmouth College, Hanover NH, (3) Norris Cotton Cancer Center, Dartmouth‐Hitchcock Medical Center, Lebanon NH

Purpose

To develop a novel, scintillator‐based imaging system for surface dosimetry in total skin electron therapy (TSET). Using a camera synchronized to linear accelerator (linac) pulses, simultaneous scintillation and Cherenkov imaging provide quantitative dosimetry measured remotely in real time.

Methods

During treatment, surface optical images were obtained using an intensified, time‐gated, camera synchronized to linac pulses located inside the linac vault. Square (2 cm² × 1 mm thick) and disc‐shaped (1 cm Ø × 1 mm thick) EJ‐212 (Elijen Technology) scintillators were calibrated and then attached to both the patient and TSET patient stand. Patients were positioned according to the modified Stanford technique and received TSET with a Varian Trilogy linac. Thermoluminescent dosimeters (TLDs) were placed adjacent to scintillators on the patient to obtain an absolute dose reference. Patient images were summed over the course of each TSET position, background subtracted, and converted into absolute dose values. Doses read from Cherenkov emission and scintillator signals were related to those reported by TLDs.

Results

The time‐gated camera system consistently provided data sufficient to generate intensity maps of scintillator light output and Cherenkov emission. For two patients undergoing TSET, cumulative images and TLD measurements were collected during two therapy sessions. Images show that the Cherenkov emission was not spatially uniform across the skin surface of patients – arms and legs exhibit less light compared to the torso area primarily due to variations in tissue optical properties. Signal from larger surface area square scintillators yielded greater pixel intensities; this signal was proportional to both dose and pixel intensities from the disc‐shaped scintillators.

Conclusion

Absolute surface dosimetry can be achieved with an accuracy of <5% of total dose by calibrating a camera system to scintillator targets. Remote imaging of both patient Cherenkov emission and dosimeter scintillation has the potential to provide real‐time absolute surface dosimetry for patients undergoing TSET.

This work has been sponsored by NIH research grants R44 CA199836, R01 EB023909 and used Shared Resources from the Norris Cotton Cancer Center core facilities, sponsored by P30 CA023106. P.Bruza is principal investigator in SBIR subaward B02463 (prime award NCI R44CA199681, DoseOptics LLC). B.Pogue is the president of DoseOptics LLC.

SA‐B‐Ballroom 5‐8‐03

Real‐Time Dose Accumulation and Radiobiological Prediction for Multi‐Metastasis Single Isocenter Stereotactic Radiosurgery

E Welch^*, A Yock

(1) Vanderbilt University Medical Center, Nashville, TN

Purpose

To demonstrate a system for real‐time dose accumulation and prediction of equivalent uniform dose for multimetastasis single isocenter stereotactic radiosurgery.

Methods

Stereotactic radiosurgery plans were created for two example brain metastases. Each plan consisted of a coplanar arc and two noncoplanar arcs at ±45° couch angles. One plan targeted a 20‐mm sphere centered at isocenter, and the other targeted an 8‐mm sphere positioned 4 cm away. The position of this latter target represented the case where multiple targets are treated simultaneously using a single isocenter. The different sizes and positions of the two targets made them differ in their sensitivity to rotational errors. For each plan, the dose delivered by each arc under the influence of clinically relevant rigid transformations was determined. At time points prior to the delivery of each arc, possible cumulative doses to be delivered were predicted by combining the dose already delivered under theoretical error conditions (1 mm & 1° and 0.2 mm & 0.2°) with 1,000 predictions of the possible remaining dose. These cumulative doses were used to make dynamic statistical predictions of the final dose volume histogram (DVH) and equivalent uniform dose (EUD).

Results

The distributions of possible DVHs and EUDs were observed to change dynamically throughout treatment in a way that depended on the size and position of the target, as well as on observed treatment delivery (P < 0.01). Smaller, off‐axis targets were more sensitive to positional errors, with a possible EUD change of over 1 Gy. Larger positional errors caused coverage losses regardless of size and position.

Conclusion

In stereotactic radiosurgery, the delivered dose depends on patient‐ and plan‐specific factors as well as on intrafractional delivery effects. Monitoring cumulative dose and radiobiological metrics during treatment would give clinicians greater awareness of the delivered dose and also greater ability to achieve their clinical goals.

SA‐B‐Ballroom 5‐8‐04

Automation of a Monte Carlo Dose Verification System for Proton Therapy

M Kaluarachchi^*, F Pirlepesov, F Xie, V Moskvin, A Faught

(1) St. Jude Children's Research Hospital, Memphis, TN

Purpose

Significant uncertainties in commercial pencil beam algorithms for proton dose calculations demonstrate a need for an independent and accurate second check system. We developed a streamlined and automated workflow to perform Monte Carlo (MC) simulations of patient treatment plans.

Methods

A TOPAS‐based model of the HITACHI spot scanning nozzle, developed and commissioned earlier, was used to calculate dose and LET. Full simulation of the nozzle ensures suitable accuracy for collection of data for future retrospective studies on late effects and toxicities while also ensuring its utility as a second check of clinical plans. A framework was developed using MATLAB to automatically handle the processes such as data exchange between the TPS and the MC system, removal of CT artifacts, and inclusion of critical RT structures. DICOM RT plan information was used to generate TOPAS inputs describing the spot scanning pattern. Resultant dose files were processed and formatted as DICOM files for analysis. Patient simulations were performed using the institutional High Performance Computing Facility.

Results

With the new framework in place, we were able to save 30–60 min otherwise spent on manual processing of data. Most importantly, now any user can compare a patient‐dose calculation from TPS and MC simulation without any knowledge of the complicated and previously manual intermediate steps.

Conclusion

Given the uncertainties in the pencil beam algorithms, it is valuable to use a MC method as an independent dose verification system. This work indicates the potential of the newly developed, automated MC second check system to be successfully implemented in the clinical workflow. This system will also be useful in generating MC data for retrospective studies. Although some of the methods we implemented to automate the patient simulations are specific to our institution, the process can be implemented in other proton therapy centers.

SA‐B‐Ballroom 5‐8‐05

Development of a Clinical Workflow for Patient‐Specific 3D‐Printed Bolus Caps for Total Scalp Irradiation

G C Baltz^*, P Chi, C Wang, D Craft, P Wong, S Hsinyi Lin, S Kry, A S Garden, R M Howell

MD Anderson Cancer Center, Houston, TX

Purpose

Total Scalp Irradiation (TSI) requires the use of bolus to achieve adequate dose to the surface. Our current standard‐of‐care technique makes a bolus cap by taping together sheets of commercial bolus material formed to the patient's head. This method is laborious, and ultimately produces a bolus cap that is difficult to reproduce and has limited conformality, leading to air gaps between the bolus and scalp. However, 3D‐printing offers a minimally labor‐intensive solution to create conformal patient‐specific bolus. The purpose of this study was to develop a clinical workflow to 3D‐print patient‐specific bolus caps for TSI.

Methods

Two python scripts were developed to automate the creation of a ready to print 3D model for a patient‐specific bolus cap from diagnostic CT scans. Several 3D printing materials were evaluated for use as a scalp bolus considering radiological tissue equivalency and material flexibility for patient comfort. A bolus cap model was generated for an anthropomorphic head phantom and 3D‐printed using two different materials and printers. We acquired CT scans of the head phantom with the bolus caps and created VMAT TSI treatment plans for each data set.

Results

Two materials were identified to be suitable for use in a bolus cap: one that can be printed in‐house, and the other by an external company. The time required to generate a patient‐specific bolus model utilizing the scripts developed for our treatment planning system is less than 15 min. Review of the CT scans showed the bolus caps to be highly conformal, with maximum air gaps of 4 mm. VMAT treatment plans generated for these two bolus caps met our clinical dosimetric criteria.

Conclusion

We developed a workflow to produce highly conformal bolus caps and reduce the labor‐intensive fabrication time. Future work will include dose verification measurements and cost analysis for in‐house verses outsourced fabrication.

SA‐B‐Ballroom 5‐8‐06

A Novel 3D Printed Liquid‐Based Brachytherapy Ultrasound QA Phantom

B Leong^*, M Ostyn, S Kim

Virginia Commonwealth University, Richmond, VA

Purpose

AAPM TG128 raises several challenges with current phantom designs used for brachytherapy ultrasound QA. No single phantom satisfies all of the recommended tests, requiring an additional setup which impedes clinical workflow. Image quality for solid phantoms is highly dependent on setup precision and is susceptible to measurement uncertainties, poor reproducibility, and sudden loss of image quality due to poor surface contact. To address these challenges, we design a novel liquid‐based phantom with customizable 3D printed components for fully integrated TG128 compatibility.

Methods

The phantom consists of four components assembled within a rectangular, plastic container. The components incorporate clinical instruments such as implant needles and templates, which are used to fix the geometric relationship of the probe and phantom to reduce uncertainties and improve measurement reproducibility. Water was chosen as the liquid medium, with speed of sound adjusted to 1540 m/s via salinity. To evaluate the performance of this phantom, we conduct a timed TG128 QA compared to the standard method for a new and experienced user.

Results

Including setup and measurement, QA was completed within 45 min using the liquid‐based phantom, compared to 70 min for an experienced user and 90 min for a new user with the standard method. The large reduction in time was primarily due to the use of liquid medium, which eliminates the challenge of surface contact encountered with solid phantoms.

Conclusion

A novel brachytherapy ultrasound QA phantom is designed to satisfy all TG128 recommendations. The choice of liquid medium improves the efficiency and reproducibility of QA measurements. Other accommodations are made to reduce the effect of setup uncertainties. The components are 3D printed and customizable to adapt to clinic‐specific needs. Eliminating the challenges and uncertainties improves characterization ultrasound performance and allows for delivery of ultrasound‐guided brachytherapy with high confidence.

An invention disclosure has been submitted and the phantom is in the process of being patented.

SA‐B‐Ballroom 5‐8‐07

Gafchromic Film‐Based Explicit Output Verification Method for Linear Accelerators Utilizing Automatic Analysis

C Guy^*, J Ojwang, S Kim, T Kim

Virginia Commonwealth University, Richmond, VA

Purpose

Independent verification of linear accelerator (linac) output is necessary during machine commissioning, and limited third‐party services are available for this purpose. In addition, these methods require time (weeks to receive results or up to a day of machine unavailability), which is often limited during the commissioning process and are not without monetary costs. A method for fast and efficient verification of linac output was developed, wherein a Gafchromic film is doubly exposed using a linac with verified output and another machine which has been recently calibrated. The procedure has been demonstrated at our facility for validation of recent output calibration during the commissioning process while awaiting third‐party verification.

Methods

For all available photon and electron beams of a newly commissioned Varian TrueBeam accelerator (6 MV, 6 FFF, 10 MV, 10 FFF, 15 MV, 6 MeV, 9 MeV, 12 MeV, 16 MeV, and 18 MeV), dose of 100 MU was delivered to one side of a piece of Gafchromic film placed in solid water using a 10 × 10 cm² field or cone. Immediately afterwards, the film and setup apparatus were transported to a second accredited accelerator, and the same doses were delivered to the opposite half of each film using the second machine. Exposed films were scanned using an Epson XL10000 scanner. The scans were analyzed using in‐house MATLAB code to quantify agreement in output between machines. Crossline and inline profiles were extracted and compared within the central 10% of the delivered field size.

Results

Automatic film analysis code was developed to facilitate the output verification. All analyzed profiles passed gamma analysis of 3%/2 mm with passing rates ranging from 99.6% to 100%. Using a 0.4% dose difference criterion, differences greater than or equal to 1 MU were detected with sensitivity of 0.925.

Conclusion

The developed method provided convenient assurance of output calibration prior to independent verification by a third party.

SA‐B‐Ballroom 5‐8‐08

Clinical Verification of Varian Representative Data for SRS Cones Through Multiple Dosimetric Methods

P Irmen^1,*, C Fitzherbert², F Zhou², C Hand²

(1) University of Pennsylvania, Philadelphia, PA, (2) Albert Einstein Medical Center, Philadelphia, PA

Purpose

To verify the representative data for Varian SRS cone output factors (OF) for a TrueBeam linear accelerator utilizing two common SRS diode detectors and Gafchromic™ film.

Methods

The Sun Nuclear EDGE detector, PTW 60012 stereotactic diode, and Gafchromic™ EBT3 film were used to measure the OF for Varian TrueBeam SRS cones. Measurements were taken for 6 MV and 6 FFF energies in a solid water phantom (EDGE and EBT3) and Sun Nuclear 1D water tank (EDGE and PTW) at 5 cm depth and 95 cm SSD. Cone diameters ranged from 4 mm to 17.5 mm. Measurements were also made for field sizes of 5 × 5 cm and 10 × 10 cm with the EDGE detector, PTW 60012 diode, EBT3 film, and Exradin A12 Ion chamber for daisy chain method comparison.

Results

The EDGE showed a maximum difference with the representative data of −1.64% for 6 MV and −1.27% for 6 FFF. The PTW show a maximum difference of −3.15% for 6 MV and −3.35% for 6 FFF. The OF measured by the EBT3 film showed maximum differences with the representative data of −8.21% for 6 MV and −9.1% for 6 FFF. Comparison of OF with and without the daisy chain correction demonstrated a maximum variation of 0.5% and 0.9% for 6 MV and 6 FFF for the two chambers.

Conclusion

Varian representative data showed agreement with the EDGE detector and PTW 60012 stereotactic diode, but showed a comparatively large difference with the EBT3 film at the smallest cones. The daisy chain correction had no significant effect on the measurements for either diode due to their ability to measure the 10 × 10 cm reference field. The large difference between EBT3 film and diode measurements may be explained by the environmental dependencies of the diodes and the inherent uncertainty in the scanning and analysis of the film.

SA‐B‐Ballroom 5‐8‐09

Characterization of X‐Ray Tube Scatter and Its Potential Impact on Occupational Radiation Exposure

A Tao^*, M Hindal, D Miller, K Fetterly

Mayo Clinic, Rochester, MN

Purpose

Occupational radiation protection procedures for angiographic procedures have been developed assuming nearly all scatter originates from the patient. The purpose of this work is to assess the contribution of scatter originating from the x ray tube on occupational radiation dose.

Methods

Scatter from a 30 × 30 × 25 cm³ PMMA phantom and that originating directly from the x ray tube was measured with an 1800 cm³ ionization chamber at an elevation of 150 cm. Scatter was measured as a function of lateral distance from the central ray (40–200 cm) for three angiography systems (A1, A2 and B). Also, system A1 was modified to include 0.5 mm Pb inside the collimator cover to surround the x‐ray beam exit window. The x‐ray technique was set to 81–85 kV with beam filtration fixed at 0.2 mm Cu and dose was normalized to system dose area product. No accessory radio‐protective shields were used.

Results

Scatter dose from the phantom was the same for all x‐ray systems. X‐ray tube scatter was 2–4 times greater from Systems A1 and A2 than System B due in part to scatter originating within a physical DAP meter. The relative contribution of tube scatter ranged from 23% (System B) to 48% (System A1) at a lateral distance of 80 cm. The modified collimator cover reduced x‐ray tube scatter of System A1 from 48% to 27%.

Conclusion

Scatter emitted from the x‐ray tube exit window was found to contribute significantly to overall scatter dose. The presence of a physical DAP meter was associated with increased tube scatter and the addition of 0.5 mm Pb to the collimator cover of System A1 reduced tube scatter to levels similar to System B. These finding demonstrate that radiation protection practices should be revised to recognize and mitigate for scatter originating within the x‐ray tubes of x‐ray angiography systems.

SA‐B‐Ballroom 5‐8‐10

Characterization of the Halcyon SX1 Multi‐Leaf Collimator System

T Lim^*, I Dragojevic, D Hoffman, E Flores‐Martinez, G Kim

University of California, San Diego, La Jolla, CA

Purpose

To evaluate the physical and dosimetric characteristics of the SX1 stacked and staggered dual‐layer multileaf collimator (MLC) on the Halcyonᵀᴹ system.

Methods

For physical characterization, we evaluated the MLC positioning accuracy due to varying gantry angles, collimator angles, leaf speed, and over time, using the EPID imager measurements. The temporal stability of the MLC positioning accuracy was derived from Machine Performance Check (MPC) data over 3 months. For dosimetric characterization, we evaluated the leaf transmission, leaf‐end effect, as well as the tongue‐and‐groove effect. Leaf transmission was measured with NIST‐traceable PTW 30013 chamber, by comparing a field with distal, proximal and both MLC layers fully closed, to an open field. Leaf‐end effect was measured using the same chamber with sweeping gap fields of varying gap sizes defined by the distal MLCs. The tongue‐and‐groove effect was investigated using the imager with fields defined by interspersed odd and even leaves for the different banks, gantry angles, collimator angles and offsets.

Results

The maximum MLC position deviation was within ±0.1 mm from the baseline of MPC measurements over 3 months, with the proximal exhibiting a greater deviation range compared to the distal MLCs. Picket‐fence deliveries with both the distal‐and‐proximal‐combination had reduced inter‐leaf, through‐leaf and leaf‐end transmission compared to delivery with distal‐only. We observed a gantry angle dependency for MLC positioning accuracy, and minimal collimator angle dependency. The measured leaf transmission factor was 0.0041 for distal‐only, 0.0040 for proximal‐only, and negligible for distal‐and‐proximal‐combination (nominal 0.0047). The measured leaf end effect was −0.0187 cm (nominal 0.01 cm). The tongue‐and‐groove effect showed minimal gantry angle and collimator angle dependency. A noticeable systematic deviation between measurements and treatment planning system handling of the tongue‐and‐groove effect warranted further investigation.

Conclusion

We have comprehensively described the performance characteristics of the SX1 dual‐layer MLC on the Halcyonᵀᴹ system.

SA‐B‐Ballroom 5‐8‐11

Characterizing the Response of Gafchromic Film to Magnetic Fields on an MRI‐Guided Linear Accelerator

I Xhaferllari^1,*, J Kim², R Liyanage³, D Du⁴, M Dumas⁵, C Liu⁶, I Chetty⁷, N Wen⁸

(1) Henry Ford Health Systems, Detroit, MI, (2) Henry ford health system, Detroit, MI, (3) Wayne State University, Detroit, MI, (4) Henry ford health system, Detroit, MI, (5) Henry ford health system, Detroit, MI, (6) Henry Ford Health System, Detroit, MI, (7) Henry Ford Health System, Detroit, MI, (8) Henry ford health system, Detroit, MI

Purpose

To characterize the effects on Gafchromic film to MR exposure time within the 0.35T magnet on the world's first MRIdian ViewRay linear accelerator.

Methods

Perturbations of EBT3 and XD Gafchromic film due to exposure time within the magnetic field were evaluated by placing the film at isocenter of the MRIdian for 12 hours prior to irradiation, after irradiation, or without any MR exposure. Films were setup at isocenter using 7.5‐cm of solid water for build‐up and 7.5‐cm of solid water for backscatter. A treatment plan consisting of nine different dose levels was delivered to each film, and polynomial fitting was performed to generate calibration curves. The orientation of the polymers was visualized using scanning electron microscopy (SEM). SEM images were acquired for unexposed film, films irradiated with MR exposure prior and after irradiation, and Gafchromic films without any MR exposure. The orientation of the crystal polymers determines dose response. The dosimetric impact of film orientation was evaluated by films exposed to MR for 12 hours prior to irradiation in both coronal and sagittal orientations.

Results

Effect of MR exposure on derived calibration curves for either film type was negligible. Correlation of calibration curves with and without exposure was >0.99. SEM images did not show a change in crystal orientation, consistent with calibration curve results. No differences were observed due to film orientation.

Conclusion

The added effects of a 0.35T magnetic field were minimal for EBT3 and XD Gafchromic film, based on comparison between film dosimetry with and without MR. These results were confirmed by experiments using scanning electron microscopy.

SA‐B‐Ballroom 5‐8‐12

Cherenkov Imaging Verification of Matched Photon and Electron Fields

P Black^*, Y Wang, C Velten, C Wuu

Columbia University Medical Center, New York, NY

Purpose

Cherenkov light emission has been shown to correlate with ionizing radiation dose delivery in solid tissue. An important clinical application of this is the real‐time verification of radiation treatment delivery in vivo. To determine the detectability of treatment field matching, we acquired Cherenkov images of photon and electron fields matched with known spacing.

Methods

Cherenkov light was captured using a PI‐MAX4 intensified charge coupled device system. A Varian Trilogy linear accelerator was operated at 6 MV or 12 MeV and 400 MU/min to deliver anterior‐posterior beams to a 5 cm thick block phantom at 100 cm or 110 cm SSD, respectively. Field overlap and gap distances of 0, 2, 5, and 10 mm were delivered and evaluated. Before delivery the 10 × 10 cm² projected light field was imaged for pixel size calibration in subsequent acquisitions. Geometric perspective distortions were corrected, using Moving Least Square transformation with landmark correspondence. Composite images were created by frame summation followed by background subtraction and evaluated, using ImageJ and MATLAB software packages.

Results

Discrepancy between delivered field size and Cherenkov light edges was 2–5 mm, with Cherenkov images systematically demonstrating a larger penumbra than the radiation field. Photon field gaps and overlaps of 2 mm were easily detected, indicating the feasibility of detecting similar spacing in a clinical situation. Cherenkov images of 0 mm gap photon fields appeared as a small field gap, but smaller than planned 2 mm gap images. Cherenkov images of matched electron fields had larger penumbras compared with matched photon fields, with known gaps as large as 5 mm appearing as overlaps.

Conclusion

This study indicates that Cherenkov imaging can be used to provide live detection of field matching error in a clinical scenario, with the most promising results demonstrated in photon‐photon field matching. Electron–electron matched fields systematically overestimated the incidence of field overlap, but this can be corrected in future clinical scenarios.

Joint Therapy‐Diagnostic Symposium – SAM
Marquis Ballroom 5‐8
How Good Imaging Can Improve Therapy Planning

SA‐C‐Ballroom 5‐8‐00

How Good Imaging Can Improve Therapy Planning

Jeffrey MoiranoModerator

University of Washington, Seattle, WA

SA‐C‐Ballroom 5‐8‐01

Y. Rong

University of California‐Davis

The Use of MRI in High Dose Rate Brachytherapy Treatment for Cervical Cancer

SA‐C‐Ballroom 5‐8‐02

M. Cao

UCLA School of Medicine

MRI Guided Adaptive Radiotherapy, Present and Future

SA‐C‐Ballroom 5‐8‐03

N. Tyagi

Memorial Sloan‐Kettering Cancer Center

Use of MRI for External Beam Treatment Planning

SA‐C‐Ballroom 5‐8‐04

Y. Hu

Mayo Clinic Arizona

Use of MRI in Radiotherapy: Technical Considerations

Imaging has played a crucial role in modern radiation therapy and has allowed for greater precision in dose optimization, dose distribution, and patient positioning. This session will focus on what is likely to be the next major clinical advancement in imaging for treatment planning: the use of Magnetic Resonance (MR) Imaging. MR imaging presents a set of unique challenges for the medical physicist in terms of image quality as well as site and patient preparation. Many of these concerns have been successfully addressed in diagnostic imaging, and a major aim of this session will be fostering a collaboration between diagnostic and therapy physicists. Clinical applications on the use of MR imaging for radiotherapy, both as a primary and secondary modality, will be presented. With a greater understanding of the imaging modality and therapeutic demands, both the diagnostic and therapy physicist will be able to contribute to improvements in patient care.

Learning Objectives:

Identify the challenges of implementing MR imaging for radiotherapyRecognize the imaging goals of MR in radiotherapyDiscuss the current and future applications of MR Imaging in radiotherapy.

Therapy Symposium – SAM
Marquis Ballroom 5‐8
IGRT: Making Effective Clinical Choices

SA‐D‐Ballroom 5‐8‐00

IGRT: Making Effective Clinical Choices

Annie HsuModerator

Stanford Cancer Center, Stanford, CA

SA‐D‐Ballroom 5‐8‐01

J. Chang

Northwell Health

IGRT: Effective Decisions with Multi‐Modality Imaging Systems

SA‐D‐Ballroom 5‐8‐02

L. Cervino

UC San Diego

Clinical Review of Imaging for Treatment Verification

Image‐guided radiotherapy (IGRT) is required for high‐accuracy high‐precision radiotherapy procedures and the incorporation of various imaging modalities into the treatment room has addressed and improved the geometrical uncertainty in radiation therapy. IGRT has greatly evolved in the last decades, and the spectrum of imaging modalities is increasing. It is a common practice to use more than one imaging modalities during the image‐guided treatment so that patient setup performed with one image modality is validated by another. This quality assurance measure might pose challenges to clinical medical physicists when results from different imaging systems do not agree with each other.This session will focus on making effective clinical choices for IGRT. We will first give an overview of the most commonly used and the newest in‐room IGRT modalities, such as simple orthogonal kV and, MV, CBCT, surface imaging, MV‐CBCT, 4D‐CBCT and MRI. We will then specify appropriate uses for each modality, paying particular attention to the imaging in the treatment of moving tumors. This will be followed by a discussion of possible sources that might lead to conflicting instructions for guiding patient setup from different imaging systems. Real clinical examples will also be used to demonstrate how to troubleshoot when problems or unexpected results occur.

Learning Objectives:

Understand the pros and cons of multimodality IGRT.Review different imaging for treatment verification approaches and image processing techniques commonly used by modern IGRT systems.Learn about the clinical implementation of imaging systems for treatment verification.Develop confidence in making proper clinical IGRT decisions based on results from multiple imaging modalities.

Diagnostic Symposium – SAM
Marquis Ballroom 1‐4
Joint Commission Diagnostic Imaging Updates

SA‐D‐Ballroom 1‐4‐00

Joint Commission Diagnostic Imaging Update

Jeffrey MoiranoModerator

University of Washington, Seattle, WA

SA‐D‐Ballroom 1‐4‐01

A. Browne

The Joint Commission

Current Standards for Diagnostic Imaging and Future Addition of Fluoroscopy

The Joint Commission (TJC) has had new and revised Diagnostic Imaging Requirements as part of their accreditation standards in effect since 2015. This session, given by a physicist representative of TJC, will discuss the current state of this program as it relates to the practice of diagnostic medical physics. A review of the requirements and expectations will be presented as well as a discussion of the common areas of noncompliance. TJC has been working on a new initiative to establish standards for fluoroscopic imaging, and the latest information on this development will be shared.

Learning Objectives:

Understand the expectations of TJC diagnostic imaging surveyorsIdentify and address the issues that most often result in surveyor findingsReview the upcoming TJC Fluoroscopic Imaging requirements.

SUNDAY, APRIL 8
Therapy Symposium – SAM
To Measure or Not to Measure for Patient‐Specific QA

SU‐A‐Ballroom 5‐8‐00

To Measure or Not to Measure for Patient Specific QA

Sotirios StathakisModerator

University of Texas Health, San Antonio, TX

SU‐A‐Ballroom 5‐8‐01

M. Miften

University of Colorado School of Medicine

Measurement‐Based Patient‐Specific IMRT QA: Fact and Fiction

SU‐A‐Ballroom 5‐8‐02

B. Yi

Univ. of Maryland School Of Medicine

Is It Safe, Non‐Measurement Based Patient Specific IMRT QA?

Measurement‐Based Patient‐Specific IMRT QA: Fact and Fiction Patient‐specific IMRT QA measurement is an important component of the process designed to identify discrepancies between calculated and delivered radiation doses. Several professional organizations (AAPM, ACR, ASTRO) have strongly recommended patient‐specific IMRT QA be employed as part of the clinical IMRT process. While the value of patient‐specific IMRT QA has been debated among medical physicists, especially whether computational methods can replace physical measurements, measurement‐based patient‐specific IMRT QA methods are still considered the gold standard. They are widely used and are the core element of most IMRT QA programs. In many centers, a QA measurement is routinely performed after a patient's IMRT plan is created and approved by the radiation oncologist. The calculations and measurements are compared and approved or rejected using the institution's criteria for agreement. If the agreement is deemed acceptable, then one infers that the delivered patient plan will be accurate within clinically acceptable tolerances. Understanding the details of methods used to evaluate the dose distributions are essential to identify and interpret the discrepancies between measurements and calculations.

Learning Objectives

1. To review published data on the achieved agreement between measurements and calculations2. To review commonly used measurement methods and discuss the advantages and disadvantages associated with each method3. To discuss IMRT QA verification metrics, their use and vendor‐implementation, including practical considerations when performing IMRT QA analysis Is it safe, non‐measurement‐based Patient‐Specific IMRT QA?

Purpose

Patient‐Specific QA (PSQA) of IMRT is to verify if beams are delivered as planned and to assure the delivered dose is the same as planned. This abstract is to review the methods of non‐measurement‐based PSQA and its advantages.

Methods

PSQA may check 3 components; (1) If all of the plan parameters such as gantry, collimator, field size, MLC positions and MU are transferred correctly from the planning system to the treatment machine, (2) Beams are delivered as planned and (3) Dose distributions are identical within tolerance range. As an example of the non‐measurement‐based PSQA, a University of Maryland method will be presented. UM has developed and adopted the non‐measurement‐based PSQA which consists of a home‐grown software to compare plan parameters between the planning system and the record and verify system, a comprehensive weekly MLC QA program and a Monte Carlo dose calculation system (currently, it is changed to a commercially available secondary dose calculation system). It is essential to measure enough number of cases and to compare the results to the planning system and the secondary calculation system when commissioning.

Results

The non‐measurement‐based PSQA has 5 advantages; (1) not only confirms that the right plan which has been approved is transferred, but also plan parameters are compared with two decimal point precision, (2) compares dose volume histograms and 3‐D dose distributions, (3) can detect dose variations from various clinical situations, such as very large patient dimension, irregular contour and heterogeneity correction, while a measurement‐based method with a single phantom cannot, (4) can deliver treatments to any machines with same beam characteristics and same comprehensive QA program and (5) QA time is shorter and can be done even in office hour.

Conclusion

The non‐measurement‐based PSQA provides more information and has many advantages over measurement‐based methods, while not compromising quality. It is safe to use non‐measurement‐based PSQA.

Learning Objectives:

To review what are to be confirmed for IMRT QA,To review the solutions of the secondary calculation,To review what should be done to implement the non‐measurement‐based IMRT QA.

Diagnostic Symposium – SAM
Marquis Ballroom 1‐4
The Zagzebski/Carson Distinguished Lecture on Medical Ultrasound

SU‐A‐Ballroom 1‐4‐00

The Zagzebski/Carson Distinguished Lecture On Medical Ultrasound

Jeffrey Moirano

University of Washington, Seattle, WA

SU‐A‐Ballroom 1‐4‐01

J. Zagzebski

University of Wisconsin

Ultrasound Instrumentation: An Important Focus for the Medical Physicist

SU‐A‐Ballroom 1‐4‐02

G. McLaughlin

Shenzhen Mindray Bio‐Medical Electronics Co., LTD.

Synthetic Aperture Imaging Methods: Technologies and Trade‐offs

Ultrasound quietly remains the most commonly used modality in diagnostic radiology. The goal of this session is to highlight innovations in ultrasound instrumentation and discuss the responsibility of the medical physicist in diagnostic ultrasound. An overview of current scanner capabilities and QA issues and requirements will be presented. Perspectives on the medical physics’ current role in quality assurance and what it can be in the future will be shared.

Learning Objectives:

Describe the components of a ultrasound quality assurance programExamine the procedures and requirements for ultrasound equipment quality controlRecognize the role of the medical physicist in diagnostic ultrasound.

Glen McLaughlin is an employee of Mindray medical systems.

Professional Symposium – SAM
Marquis Ballroom 5‐8
Medical Physics Information Technology

SU‐B‐Ballroom 5‐8‐00

Medical Physics Information Technology

Matthew Meineke

Ohio State University, Columbus, OH

SU‐B‐Ballroom 5‐8‐01

W. Feng

Bayhealth Medical Center

IT Basics and Trouble Shooting for the Clinical Medical Physicist

SU‐B‐Ballroom 5‐8‐02

B. Curran

Virginia Commonwealth University Medical Center

Current Standards for Information Exchange in Radiation Oncology: DICOM, DICOM‐RT, and HL7

SU‐B‐Ballroom 5‐8‐03

P. Balter

UT MD Anderson Cancer Center

Database Basics Including Applications in Radiotherapy for Safety and Efficiency

SU‐B‐Ballroom 5‐8‐04

C. Mayo

University of Michigan

If only my planning system could…. Using scripting to push the envelope on clinical capabilities of treatment planning systems

IT Basics and Trouble Shooting for Clinical Medical Physicist — Wenzheng Feng

Radiation oncology (RO) is an informatics‐based discipline; actually RO is one of the most IT‐demanding areas of the hospital. Since medical physicists have the best understanding of the overall clinical process, medical physicists should have ability to perform many RO‐specific IT tasks.

In this symposium we will review IT knowledge essential to medical physics and illustrate sample solution to some typical clinical problems. This session will cover the concepts involved in networking, data transfer, DICOM, DICOM‐RT and HL7 connectivity, database operations and Scripting for IT.

There are many hardware, software, and networking issues in RO. The initial response to IT‐related problems during treatment must be of high priority and prompt within minutes. Optimally, the first‐line response comes from medical physicists, after triage the issue, solve it by their self or contact appropriate personnel, like IT staff, engineer, and vendor. Networking interconnects all the radiation oncology devices together, efficient and reliable data transferring is critical to clinical operations. Network infrastructure will be explained with clinical examples; real‐world scenario will be presented to illustrate the typical trouble shooting steps, typical trouble shooting software/tool will be introduced as well.

Current Standards for Information Exchange in Radiation Oncology: DICOM, DICOM‐RT, and HL7 — Bruce Curran

Prior to the early 1990s, each vendor developed a unique protocol for exchanging information; the result was a chaotic array of software interfaces and translation programs for acquisition of imaging information in radiation oncology. DICOM (Digital Imaging for Communication in Medicine) was developed to provide a standards‐based protocol for image data exchange. This standard has been extended to include radiation therapy planning, dose, and verification data and now workflow. We will discuss the basic structure of DICOM, its mechanisms for finding compatible transfer syntaxes and mutual capabilities for communication, and what the medical physicist needs to know to setup and maintain DICOM interfaces in radiation oncology.

Database Basics including applications in Radiotherapy for Safety and Efficiency — Peter A. Balter

Databases are the foundation of many of our clinical systems and the ability to understand them is vital to practice in a radiotherapy clinic. We will discuss database fundamentals and then show how several commercial products uses databases. We will discuss the design and creation of research and task‐specific databases as well. We will have real world examples of data extraction from commercial databases for clinical support and research using both databases tools, such as the SQL management studio, and programing examples. We will also discuss backup strategies and auditing for enterprise level databases.

“If only my planning system could….” Using scripting to push the envelope on clinical capabilities of treatment planning systems — Chuck Mayo

The landscape of essential skills and roles for medical physicists is shifting. In this new frontier, ability to code in production level languages to take advantage of application programming interfaces (APIs) built into treatment planning systems (TPS) is increasingly valuable. With these APIs end users are enabled to fill many gaps between intrinsic functionality of the vended system and a wide range of clinic‐specific needs such as reporting, automated planning, bio‐correction, plan evaluation, etc. We will discuss development environments and API capabilities for a few TPSs, review some core coding concepts used in these approaches and provide examples of end user scripts.

Learning Objectives:

Refresh the basics of computer networking and gain familiarity of typical trouble shooting toolsUnderstand the fundamentals of connectivity with DICOM, DICOM‐RT and HL‐7Become familiar with database concepts to improve troubleshooting skills4. Practice scripting programming with vendor support.

Diagnostic Symposium – SAM
Marquis Ballroom 1‐4
CT Dosimetry and Applications

SU‐B‐Ballroom 1‐4‐00

CT Dosimetry and Applications

William Sensakovic

Florida Hospital, Orlando, FL

SU‐B‐Ballroom 1‐4‐01

M. Arreola

University of Florida

CT Dosimetry in the Clinical Environment: Methods and Analysis

SU‐B‐Ballroom 1‐4‐02

M. Mahesh

Johns Hopkins University

Cardiac CT Principles and Radiation Doses

In the field of diagnostic radiology, Computed Tomography (CT) is the “go to” modality for structural patient information. The utility of the modality is unquestionable, however, the cost of its diagnostic utility is a relatively high radiation dose imparted to the patient. As such, it is imperative that a clinical physicist understand CT dosimetry to calculate patient dose reconstructions for safety review and tracking. Further, knowledge of the underlying principles of CT are necessary to understand how to optimize scanning protocols to only deliver the necessary radiation dose for the desired task. Physicist training in the effective use of CT is especially important for specialty scans that are traditionally not as widely discussed, such as cardiac CT.

This session will review both current and new methodologies for CT dose calculations with a focus on practical implementation. It will further review the basics cardiac CT and discuss techniques implemented to optimize patient dose.

Learning Objectives:

Understand and implement methods for CT dose reconstruction.Understand the basics of cardiac CT acquisition.Explain techniques to optimize patient dose during cardiac CT scanning.

Therapy Symposium
Marquis Ballroom 5‐8
AAPM TG 275: Live Demonstration of Chart Checks

SU‐C‐Ballroom 5‐8‐00

AAPM TG 275: Live Demonstration of Chart Checks

Annie HsuModerator

Stanford Cancer Center, Stanford, CA

SU‐C‐Ballroom 5‐8‐01

G. Kim

University of California, San Diego

EBRT Plan Review – Eclipse/ARIA

SU‐C‐Ballroom 5‐8‐02

A. Greener

A Medical Center

EBRT Plan Review – Pinnacle/Mosaiq

SU‐C‐Ballroom 5‐8‐03

S. Parker

University North Carolina

EBRT Plan Review – RayStation/Mosaiq

SU‐C‐Ballroom 5‐8‐04

P. Johnson

University of Miami

HDR Plan Review — Oncentra/Aria

The pretreatment plan review is a fundamental task performed by the majority of therapy medical physicists and is of great interest to clinical physicist. As seen in a recent survey performed by TG275, however, there is great variability in how this task is done. Factors contributing to this variability include differences in training, environment, and perception as to which failure modes present the highest risk to the patient. In this session, this issue will be addressed through a live demonstration of plan reviews including conventional external beam radiotherapy, IMRT, SBRT, and brachytherapy treatment plans. The session will begin with a brief overview of plan checking and the recommendations of TG275. Each presenter will remotely connect to their local system and review an anonymized case. Throughout the demonstration each presenter will discuss a systematic approach to plan review using the recommendations of TG275. Multiple electronic systems (TPS/OIS) will be included such that audience can see how similar items are checked across different platforms. At the end of the demonstration a Q&A session will allow members of the audience to share their own experiences performing plan reviews and discuss any items which they feel were not covered adequately by the demonstrated reviews.

Learning Objectives:

Learn the fundamental aspects of the physics plan review.Understand how plan reviews are performed across different platforms.Discover relevant items to check which may have been previously unknown or underappreciated.

Professional Symposium – SAM
Marquis Ballroom 1‐4
Navigating IT Requirements in Today's Electronic Environment

SU‐C‐Ballroom 1‐4‐00

Navigating IT Requirements in Today's Electronic Environment

Matthew MeinekeModerator

Ohio State University, Columbus, OH

SU‐C‐Ballroom 1‐4‐01

B. Murray

OMPC Therapy, LLC and OMPC Diagnostics, LLC

Current and Future IT Applications in the Clinical Medical Physics World

SU‐C‐Ballroom 1‐4‐02

S. Wilson

Riverside Methodist Hospital

Developing a Relationship with Your IT Department: Understanding Modern Technology Requirements

Current and Future IT Applications in the Clinical Medical Physics World — Bryon M. Murray, M.S., DABR

Medical physicists have historically been the source of expertise in the utilization of computers and software systems in the clinical environment. As software and hardware systems have evolved, the complexity of information technology (IT) has increased, resulting in the IT professionals managing all aspects of computing software and hardware. Understanding the current applications and the different IT requirements will help the clinical medical physicist in the process of specification, selection and ultimately implementation of these systems.

Developing a relationship with your IT department: Understanding modern technology requirements‐ B. Scott Wilson

The role of information technology (IT) has expanded and become extremely complex in the last several years. Understanding these complexities and the requirements IT professionals must follow in ensuring the security and integrity of healthcare information at all levels is paramount to any practicing health professional. An overview of current requirements, networking trends, security, and new technologies will be presented.

Learning Objectives:

Review progression of technology in the medical physics clinical environmentBecome familiar with existing and future technologies including hardware and software typically used in the radiation oncology and radiology environmentsUnderstand the relationship of IT to existing hardware and software systems as well as potential future requirements.

Therapy Symposium – SAM
Marquis Ballroom 5‐8
AAPM TG 210 Review – Conventional LINAC Acceptance Testing

SU‐D‐Ballroom 5‐8‐00

AAPM TG 210 Review — Conventional LINAC Acceptance Testing

Sotirios Stathakis

University of Texas Health, San Antonio, TX

SU‐D‐Ballroom 5‐8‐01

Empowering the Physicist in the Linac Acceptance Process, the TG210‐ Perspective

A. Perez‐Andujar

University of San Francisco:

With more sophisticated linear accelerators, it is necessary to re‐evaluate the steps associated with the acceptance testing process (ATP). This is especially relevant given the requirement of tighter tolerances for stereotactic treatments, as well as more complex component of the linear accelerator. Currently, the vendor mainly guides the ATP process and there are not enough updated guidelines for the physicist regarding this process. The purpose of the AAPM Task Group Report 210 (TG 210) is to provide the physicist with the necessary tools at the time of performing a linac ATP. TG 210 provides updated recommendations and tolerances on the test to be performed and it also provides information regarding the considerations that have to be taken before the ATP process starts.

Learning Objectives:

To present the test involved in the ATP process with its associated tolerances;To present which aspects should be considered during the purchasing contract and the installation processTo discuss the precautions that should be taken during any major component replacements and upgrades that will require additional acceptance testing.

Mammography Symposium – SAM
Marquis Ballroom 1‐4
The Art of the Image in Mammography

SU‐D‐Ballroom 1‐4‐00

The Art of the Image in Mammography

Nicole Ranger

Aspirus Wausau Hospital, Wausau, WI

SU‐D‐Ballroom 1‐4‐01

B. Schueler

Mayo Clinic

Artifacts in 2D and 3D Breast Imaging: Their Origin, Presentation, and Remediation

Artifacts visible in full field digital mammography (FFDM) and tomosynthesis images are distracting and may compromise accurate diagnosis. The purpose of this presentation is to familiarize the participant with various types of 2D and 3D image artifacts, along with their causes. Examples from both quality control and patient imaging will be included. When appropriate, the corrective action to eliminate the artifact will also be discussed.

Learning Objectives:

1.Identify common artifacts found in FFDM and tomosynthesis images2.Determine causes of various artifacts3.Describe how to remediate artifacts when possible.

MONDAY, APRIL 9
Therapy Symposium – SAM
Marquis Ballroom 5‐8
Automation in Therapy: The Future is Now

MO‐A‐Ballroom 5‐8‐00

Automation in Therapy: The Future Is Now

Sotirios Stathakis

University of Texas Health, San Antonio, TX

MO‐A‐Ballroom 5‐8‐01

C. Mayo

University of Michigan:

Purpose

Automation in Plan Quality Assurance (QA)

MO‐A‐Ballroom 5‐8‐02

L. Court

UT MD Anderson Cancer Center

Automation in Treatment Planning

Major vendors of treatment planning systems are providing application programming interfaces (APIs) that allow not only reading information from the treatment planning system (TPS) to support reporting but also writing data back to support automated creation and optimization of treatment plans. This opens the door for end users to make tremendous gains in efficiency, consistency and quality. In this session, we will explore examples of how two institutions are using these API capabilities to improve planning and QA processes for their own and other clinics. Development of automated head and neck planning approaches supporting clinical practice in the US and extension to support developing countries will be presented. Recent development of new plan evaluation tools using statistical dose volume histogram dashboard visualizations and metrics have been reported. Use of these in conjunction with automated planning approaches to use historical context to improve plan evaluation and teaching will be discussed. These will show that the future is now for combining standardizations, statistics and code to bring automation into our planning processes.

Learning Objectives

Understand a practical implementation of automation for radiotherapy treatment planningUnderstand a practical implementation of automation for treatment plan evaluation and QABe able to discuss the likely future of automation in radiotherapy.

NCI and Varian Medical Systems.

Mammography Symposium – SAM
Marquis Ballroom 1‐4
Future Directions in Breast Imaging QC and Dosimetry

MO‐A‐Ballroom 1‐4‐00

Future Directions in Breast Imaging QC and Dosimetry

Nicole Ranger

Aspirus Wausau Hospital, Wausau, WI

MO‐A‐Ballroom 1‐4‐01

D. Pfeiffer

Boulder Community Health

Introduction to the ACR Breast Tomosynthesis QC Program

MO‐A‐Ballroom 1‐4‐02

A. Hernandez

University of California‐Davis

The History, Current Practice, and Future of Breast Imaging Dosimetry

Part 1: The American College of Radiology released its Digital Mammography QC Manual in 2017 and it became effective July 2017. Adoption of the new QC manual has been slow due to the fact that it does not cover Digital Breast Tomosynthesis (DBT), meaning that facilities with DBT or planning on adding it soon must continue using the manufacturer's QC manual. The ACR's Quality Assurance in Mammography Subcommittee has developed a DBT supplement to the DM QC Manual. Once approved by FDA, this supplement, along with the DM QC Manual, will be an alternative standard, allowing facilities to elect to use it in place of the manufacturer‐mandated QC programs. This talk will introduce attendees to the proposed supplement, detailing the testing protocols involved. The steps for gaining approval for the supplement will be outlined and an update on the current status will be provided.

Learning Objectives:

1.Understand the intent of the Digital Breast Tomosynthesis supplement to the ACR Digital Mammography QC Manual.

2.Understand the differences between the proposed QC test protocols and the current manufacturers’ protocols for DBT QC.

3.Learn the anticipated timetable for implementation of the ACR DBT Supplement.

Part 2: Mammography based on projection x‐ray imaging is the current gold standard for breast cancer screening, even as the technology has changed dramatically over the years, including the migration from screen‐film to digital mammography using detector systems based on 2D‐breast imaging and later, 3D breast imaging or Tomosynthesis. Concurrently, with the advent of truly three‐dimensional breast imaging modalities such as MRI and breast CT, previous assumptions regarding breast geometry and composition have changed as well. Knowledge of the 3D breast anatomy gained from these new modalities has informed the dosimetry assumptions of 2D breast imaging. This presentation will discuss past and present breast dosimetry modeling, and how 3D breast anatomy learned from breast CT has changed assumptions about skin thickness, breast density, and breast density distribution. This session will also address details associated with the newly adopted Dance method by the ACR; and describe the similarities and differences in comparison to prior ACR methods for the estimation of the mean glandular dose in mammography.

Learning Objectives

Be able to describe how breast dose is impacted by changes in target/filter combinations, kV, and breast thickness/composition.Understand the differences (and similarities) between the Dance method and the prior ACR method.Understand how to implement the Dance method in terms of look up tables, assumptions made, etc.Be able to discuss how the simple breast dosimetry model fails to accurately reflect actual patient dose and give reasons for this failure.Gain insight into future directions in dosimetry modeling and estimation techniques.

Therapy Symposium – SAM
Marquis Ballroom 5‐8
4D Image Choices and Pitfalls

MO‐B‐Ballroom 5‐8‐00

4D Image Choices and Pitfalls

Matthew Meineke

Ohio State University, Columbus, OH

MO‐B‐Ballroom 5‐8‐01

P. Xia

The Cleveland Clinic Foundation

What Planning CT Should Be Used for Lung SBRT, Free‐breathing CT, MIP‐CT, or AIP‐CT?

MO‐B‐Ballroom 5‐8‐02

T. Pan

UT MD Anderson Cancer Center

Mitigation of the Effects of Irregular Respiration in 4D‐CT

Which Planning CT Should Be Used for Lung SBRT, Free‐breathing CT, MIP‐CT, or AIP‐CT? Ping Xia, PhD — The Cleveland Clinic Foundation

Using stereotactic body radiotherapy (SBRT) for early staged, medically inoperable, lung cancer has been dramatically increased recently. To account for the tumor motion, four‐dimensional (4D) — CT is often acquired to assess the magnitude of tumor motion. The internal target volume (ITV) can be directly delineated on the 4D‐CT or CT in the cine mode. Alternatively, the ITV can be delineated on the maximum intensity projection (MIP)‐CT. Because of 4D‐CT involving multiple phases, directly using 4D‐CT for treatment planning is clinically challenging. Free‐breathing (FB) CT, MIP CT, averaged intensity project (AIP‐ derived from 4D‐CT) CT, or a single phase CT (mid‐inspiration CT) are used for treatment planning. There is no consensus on which CT should be used for planning CT. Furthermore, when daily cone‐beam CT is applied for tumor localization, selection of a planning CT, which is the reference CT during IGRT, becomes more important. The objectives of this education session are to discuss advantages and disadvantages of choosing above mentioned planning CTs and provide cautions to clinical physicists about the potential pitfalls when choosing one of these CTs for treatment planning.

Mitigation of the Effects of Irregular Respiration in 4D‐CT — Tinsu Pan, PhD — M.D. Anderson Cancer Center

Artifacts caused by irregular respiration are a major source of error in 4D‐CT imaging. New techniques for cine and helical 4D‐CT to combat the irregular respiration in 4D‐CT have been developed. For cine 4D‐CT, an approach to mitigate the impact of irregular respiration without new hardware, software or off‐line data‐processing on the GE CT scanner has been developed and can be applied in the clinic today. For helical 4D‐CT, statistical analysis of the breathing signal for projection binning and incorporation of an artifact measure through phase and local amplitude‐based reconstructions have been proposed. It is the purpose of this symposium to provide an overview of the 4D‐CT and to demonstrate the new and practical techniques for removing the irregular respiration and mitigating the impact of irregular respiration in 4D‐CT.

Learning Objectives:Understand differences between 4D‐CT, MIP, and AIPUnderstand challenges of using 4D‐CT for treatment planningUnderstand potential pitfalls of using FB‐CT, MIP‐CT, and AIP‐CT as the treatment planning CTsUnderstand how to align CBCT to the reference CT during daily IGRT.Learn the basics of 4D‐CT6. Identify the sources of artifacts in 4D‐CT7. Lean new techniques to combat the artifacts in 4D‐CT.

Ping Xia, PhD: Research grant from Phillips Medical Systems; Tinsu Pan, PhD: Nothing to declare

Diagnostic Symposium – SAM
Marquis Ballroom 1‐4
 Fluoroscopy Patient Peak Skin Dose Monitoring and Tracking

MO‐B‐Ballroom 1‐4‐00

Fluoroscopy Patient Peak Skin Dose Monitoring and Tracking

Jeffrey Moirano

University of Washington, Seattle, WA

MO‐B‐Ballroom 1‐4‐01

P. Lin

Virginia Commonwealth University Medical Center

Preparation for Peak Skin Dose Estimation

MO‐B‐Ballroom 1‐4‐02

F. Corwin

Virginia Commonwealth University

Applying Corrections and Sample Cases with a Real‐Time Dosimetry System

MO‐B‐Ballroom 1‐4‐03

A. Goode

University of Virginia Health Systems

Clinical Experiences with a Patient Skin Dose Monitoring and Tracking Program

MO‐B‐Ballroom 1‐4‐04

J. Clark

Virginia Commonwealth University Medical Center:

Institutional Infrastructure for Fluoroscopy Exposure Monitoring and Tracking

Fluoroscopic imaging procedures can carry a significant radiation dose and are capable of producing radiation‐induced skin injuries. This session will discuss the implementation and utilization of a patient radiation dose monitoring and tracking program (PRDMT) for fluoroscopic imaging procedures. Modern equipment is required to report the reference point air kerma (RPAK), but further processing and corrections are required for accurate estimation of Peak Skin Dose (PSD). Institutional infrastructure should be established to evaluate and classify the PSD, as well as monitor and track patients who have received high doses. The PRDMT should allow for assessment of potential injury, assist in patient follow‐up, and provide accurate dosimetry information for risk management. Experience from multiple centers will be shared along with applicable best practices.

Learning Objectives:

Recognize the importance of establishing a patient dose monitoring and tracking program (PRDMT)Identify the components that comprise a PRDMTApply correction factors necessary to calculate accurate peak skin doseDesign an infrastructure to identify and monitor patients who have received high radiation doses.

Professional Symposium
Marquis Ballroom 1‐4
ABR Update & Regulatory Update

MO‐C‐Ballroom 1‐4‐00

ABR Update & Regulatory Update

Matthew MeinekeModerator

Ohio State University, Columbus, OH

MO‐C‐Ballroom 1‐4‐01

J. Seibert

C Davis Medical Center

ABR MOC Update

MO‐C‐Ballroom 1‐4‐02

M. Reiter

Capitol Associates, Inc.:

On the Hill: What Does the New Legislative Year Look Like?

MO‐C‐Ballroom 1‐4‐03

J. Elee

LA Department of Environmental Quality:

Summary of Radiation Medical Events

MO‐C‐Ballroom 1‐4‐04

R. Martin

AAPM:

Update of Radiation Safety Issues

ABR Update — J. Anthony Seibert

The American Board of Radiology (ABR) has had a Maintenance of Certification (MOC) program for ten years. During that time the program has evolved. The MOC program consists of four parts.

Part 1 – Professional StandingPart 2 – Lifelong Learning and Self‐AssessmentPart 3‐ Assessment of Knowledge, Judgment and SkillsPart 4 –Practice Quality Improvement.

All four elements have evolved in recent years. This presentation will review the MOC program and will provide information on how each part of the program has evolved.

What Does the New Legislative Year Look Like? — Matt Reiter, AAPM Lobbyist

This session will provide an overview of the current environment for federal health policy. The presentation will address policy changes that will affect the clinical work of medical physicists.

In addition, the presentation will discuss AAPM's efforts to maintain patient access to radioisotopes and address any draft bills introduced and/or the potential of such bills being introduced in Congress to mandate the use of alternative technologies and/or limit access to radioactive sources. The presentation will examine AAPM's role in educating legislators and others on the safe and secure use of radioactive materials and the benefit from utilizing these sources in treatment of cancer and providing quality patient care.

CRCPD Medical Event Reporting‐the How and Why — Jennifer Elee

The presentation will address the Conference of Radiation Control Program Directors’ (CRCPD's) efforts to create a database of radiation medical events. The CRCPD collects events from all states with reporting requirements in place. The CRCPD H‐38 Committee on Radiation Medical Events is overseeing the development and maintenance of a national database of radiation medical events, providing a single point for all states to input events into a single database. The CRCPD Committee on Medical Events works with AAPM to produce an annual summary of events which includes a written report and summary presentation given at the CRCPD annual meeting each year. Evaluation of data is done in consultation with advisors, resource individuals, and other experts in the field, and the CRCPD uses the data to inform interested parties on trends, root causes, and methods for improvement. The CRCPD has been collecting events since 2011. The presentation will include a summary of the radiation medical event data collected and discuss the lessons learned so far.

Medical Use of Radiation: Radiation Safety Issues — Richard Martin

This session will provide a brief update of radiation safety issues impacting medical physicist practices. The presentation will examine pending U.S. Nuclear Regulatory Commission (NRC) activities, provide the status of the NRC's re‐evaluation of Category 3 source security and accountability, and look at other regulations, legislation and case law impacting radiation safety, patient access to radioactive sources, and medical event reporting.

The presentation will include a discussion of the Patient Safety and Quality Improvement Act (2005), which spurred growth of incident learning systems, including the Radiation Oncology Incident Learning System (RO‐ILS), and it will update attendees on the evolving law relating to the patient safety work product privilege.

Learning Objectives:

To review and understand the four parts of the ABR MOC programTo learn the most recent updates to the MOC program and how they affect current diplomates.To understand the political environment impacting medical use of radiation.To learn about AAPM's advocacy related to medical use of radiation and access to radioisotopes.To understand the CRCPD reporting system.To promote event reporting and incident learning at all levels.To discuss the numbers and types of events reported to CRCPD from 2011–2017.To learn about current issues in the radiation safety arena.To understand issues related to medical use of radiation that may impact patient access to radioactive sources.To understand the evolving law on incident learning systems and the patient safety work product privilege.

Therapy Symposium – SAM
Marquis Ballroom 5‐8
Special Topics: TBI and Brachytherapy

MO‐D‐Ballroom 5‐8‐00

Special Topics: TBI and Brachytherapy

Annie Hsu

Stanford Cancer Center, Stanford, CA

MO‐D‐Ballroom 5‐8‐01

X. Gu

UT Southwestern Medical Center:

Advances in TBI

MO‐D‐Ballroom 5‐8‐02

J. Prisciandaro

University of Michigan

MRI for HDR Treatment Planning

In this session, we explore the technological advances in two exciting fields, total body irradiation (TBI) and magnetic resonance image‐based brachytherapy treatment planning.

Conventional TBI techniques adopt large treatment fields with or without lung blocks to irradiate the patient's entire body, standing or in the decubitus position, at an extended source‐to‐skin distance, e.g., 5 m. The technique is exhausting for immunocompromised patients and the overall treatment time is often extended because of compliance issues.

Significant technological advances have been introduced by delivering radiation using multiple segmented or modulated beamlets, intensity‐modulated radiation therapy (IMRT) which allows for greater sculpting of radiation doses to fit treatment targeted regions while sparing adjacent critical organs. Total marrow irradiation (TMI) becomes feasible with IMRT technique advancement. In this part of presentation, we will review conventional TBI techniques and the recent development of dedicated TBI irradiators, followed by descriptions of new TBI techniques using IMRT, including floor‐based inverse‐planned modulated‐arc TBI (MATABI), volumetric arc therapy‐based TBI (VMAT‐TBI), and TMI with helical Tomotherapy. Clinical experience with advanced modulation radiotherapy will be shared. Future technical and clinical development of TBI/TMI will be discussed.

As computed tomography (CT) and magnetic resonance imaging (MRI) have become more widely available in clinics and hospitals, brachytherapy imaging has undergone a transition from the use of planar to volumetric imaging. Over the last two decades, there has been increasing interest in MRI either in conjunction with CT or independently for image guidance. Compared with CT, MR images have superior soft tissue resolution that has demonstrated a clear advantage for HDR brachytherapy.

Although GEC‐ESTRO has published a series of recommendations to assist in the standardization of image‐based brachytherapy treatment planning, their scope is limited to the experience of a few key European institutions using magnetic field strengths that did not exceed 1.5T. The recently published ICRU 89 report provides a good description of current volumetric imaging for the cervix with the addition of 4D adaptive target concepts and updated radiobiology and DVH parameter reporting for target and organs‐at‐risk. With the approval of Task Group 303 on MRI Guidance in HDR Brachytherapy — Considerations from Simulation to Treatment, the AAPM has recognized the need for developing guidance on MRI‐guided brachytherapy from a US perspective. This segment of the presentation will provide an overview of task group 303 and their initial recommendations for MR‐guided HDR brachytherapy for gynecologic and prostate cancers.

Learning Objectives:

Understand the principles and applications of TBI/TMI for bone marrow transplantation.Learn about recent technological advances of TBI/TMI using modulated radiotherapy.Learn clinical experience of new TBI/TMI treatment techniques and discuss future technique development and clinical implementation.Understand the rationale for transitioning to MR‐guided brachytherapy for gynecologic and prostate cancers.Understand the process of commissioning, QA, and clinical implementation of MR‐guided brachytherapy.Discuss workflow options for implementing MR‐guided brachytherapy for gynecologic and prostate cancers.

Diagnostic Symposium – SAM
Marquis Ballroom 1‐4
DEXA Physics and Applications

MO‐D‐Ballroom 1‐4‐00

DEXA Physics and Applications

William SensakovicModerator

Florida Hospital, Orlando, FL

MO‐D‐Ballroom 1‐4‐01

D. Gauntt

UAB Medical Center:

Dual Energy X‐Ray Absoptiometry (DXA): Science, Technology, and Practice

Dual Energy X‐Ray Absorptiometry (DXA)is a radiologic technique used to evaluate the composition of tissues in the body. Its most widely known application is in bone densitometry, but it is also used to determine whole‐body composition (bone, lean, and fat). The fundamental science behind DXA is similar to that of dual‐energy imaging, but with variations important to its uses as a quantitative modality rather than an imaging modality.

This session will explore the variations in DXA technology from its roots in Dual Photon Absorptiometry to the clinical scanners in use today, and the kinds of QA testing typically performed on DXA scanners.

Learning Objectives:

Understand the fundamental science behind DXAUnderstand the variations in technology between models of DXA scannersUnderstand the kinds of QA testing done on DXA scanners.

TUESDAY, APRIL 10
Therapy Symposium – SAM
Marquis Ballroom 5‐8
In the Era of Consolidation: Making Physics Minutes Count

TU‐A‐Ballroom 5‐8‐00

In the Era of Consolidation: Making Physics Minutes Count

Sotirios StathakisModerator

University Of Texas Health, San Antonio, TX

TU‐A‐Ballroom 5‐8‐01

A. Riegel

Northwell Health:

Resource Integration and Management in Multi‐Site Radiation Oncology Departments

TU‐A‐Ballroom 5‐8‐02

M. Price

Vanderbilt University Medical Ctr.:

Staffing Models for Multi‐Site Institutions

TU‐A‐Ballroom 5‐8‐03

L. Potters

Northwell Health:

Command and Control in the Era of Consolidation

Healthcare has entered an age of consolidation. Independent hospitals and clinics are merging to form sizable regional health institutions to increase bargaining power and defray costs. As a result, formerly independent radiation oncology clinics are growing into multisite departments. Though consolidation may yield benefits for the health system as a whole, individual radiation oncology clinics may struggle with many aspects of the merger.

In this session, the speakers will discuss the stickier aspects of consolidation including staffing models, equipment and resource sharing, technological integration, standardization, and connecting workplace cultures. Attendees will be encouraged to discuss their own experiences with consolidation.

Learning Objectives:

Explore common staffing models for multisite institutionsDefine potential benefits and pitfalls of technological and resource integrationDiscuss successful leadership techniques for integration of staff after consolidation and encouragement of treatment standardization.

Mammography Symposium – SAM
Marquis Ballroom 1‐4
Breast Imaging in the Clinic

TU‐A‐Ballroom 1‐4‐00

Breast Imaging in the Clinic

Nicole Ranger

Aspirus Wausau Hospital, Wausau, WI

TU‐A‐Ballroom 1‐4‐01

S. Friedewald

Northwestern University:

Clinical Breast Imaging: What Every Physicist Should Know

TU‐A‐Ballroom 1‐4‐02

W. Geiser

UT MD Anderson Cancer Center:

Multi‐Modality Stereotactic Breast Imaging Biopsy Systems

This two‐part session will focus on breast imaging in the clinic with an introduction to Clinical Mammography followed by a presentation on multimodality breast imaging biopsy systems and the new ACR Breast Imaging Center of Excellent Accreditation.

Part 1: Clinical Breast Imaging: What Every Physicist Should Know

Screening mammography is a hotly debated topic and generates much discussion. Additionally, the recent guidelines put forth by the United States Preventive Services Task Force (USPSTF), the American Cancer Society (ACS) and the National Comprehensive Cancer Network (NCCN) aid to the confusion regarding when to commence and how often to screen patients. This talk will be focused on sorting through these recommendations, as well as reviewing newer technologies such as digital breast tomosynthesis (DBT) and its future role in breast imaging. Finally other screening techniques such as whole breast screening ultrasound and abbreviated MRI will be reviewed.

Learning Objectives:

Identify current guidelines regarding screening mammographyDiscuss the benefits and future of digital breast TomosynthesisReview the indications for whole breast ultrasound and abbreviated breast MRIPredict the future of breast imaging

Part 2: Breast Biopsy from the Physics Perspective.

Breast biopsies are performed using several different modalities. These modalities include x‐ray imaging (stereotactic and tomosynthesis‐guided biopsies) ultrasound‐guided biopsies and MRI‐guided biopsies. In the near future, we may also see breast biopsies routinely being performed using molecular breast imaging (MBI) and contrast‐enhanced digital mammography (CEDM).

In October 2007 the American College of Radiology started a new program called the Breast Imaging Center of Excellence (BICOE). The BICOE designation is awarded to breast imaging centers that have earned accreditation in the ACR's voluntary breast‐imaging accreditation programs including breast ultrasound with ultrasound‐guided biopsy, stereotactic breast biopsy, breast MRI as well as the mandatory mammography accreditation program.

This lecture will provide the medical physicist with the knowledge he or she will need to assist their women's imaging facilities obtain and maintain accreditation in stereotactic breast biopsy, ultrasound‐guided breast biopsy as well as how to help set up a program for performing breast biopsies using MRI guidance. Future directions in breast biopsy using MBI or CEDM will also be discussed.

Learning Objectives:

Review and understand the test requirements for stereotactic breast biopsy systems and ultrasound systemsUnderstand how MRI‐guided biopsies are performed.

Professional Symposium – SAM
Marquis Ballroom 5‐8
Peer Support and Mentorship

TU‐B‐Ballroom 5‐8‐00

Peer Support and Mentorship

Brent ParkerModerator

University Texas Medical Branch of Galveston, Galveston, TX

TU‐B‐Ballroom 5‐8‐01

Y. Rong

University of California‐Davis:

Mentoring 101

TU‐B‐Ballroom 5‐8‐02

R. Stern

UC Davis Cancer Center:

Mentoring in an Academic Cinic

TU‐B‐Ballroom 5‐8‐03

S. Evans

Yale University:

Rationale for Peer Support

TU‐B‐Ballroom 5‐8‐04

J. Johnson

Landauer Medical Physics:

Needs Assessment of Peer Support in Medical Physics

TU‐B‐Ballroom 5‐8‐05

Y. Rong

University of California‐Davis:

Panel Discussion

Medical Physicists have been shown to have high level of stress in the workplace. Social support from peers has been shown to be desired by physicians, and has also been recently shown to be extremely cost effective. Despite this, few programs offer social support to their staff members from their peers. In a recent AAPM associated survey of medical physicists, social support had been sought by medical physicists for personal physical illness (78.63%), involvement in a medical error (73.94%) or adverse patient outcome (75.17%). They also sought social support in the setting of personal fatigue (33.2%) or burnout (44.3%). This program would discuss the data behind peer support, the problem of the second victim, and would share strategies for offering peer support. Practical advice on offering peer support and challenges therein would be given.

Learning Objectives:

Describe second victim syndrome and the cost of this problem (personal, health system)Discuss the data on medical physicists and desire for peer supportDescribe effective peer support techniques after a medical error.

Mentor relationships are important to a medical physicist's career. Young physicists will start out as mentees, but as their careers develop, they will find themselves becoming mentors as well. The transition from mentee to mentor may not always be easy and smooth, but it has definitely been overlooked. Mentoring is part of the leadership skill set that one cannot naturally own, but those skills can be nurtured and trained. The goal of this professional symposium is to share experience and provide advices from mid‐career physicists and senior mentors. The session aims to empower junior or mid‐level physicists with fundamental elements of how to be effective and successful in their mentoring roles.