Abstract
Background:
We assessed loco-regional control with omission of intentional primary site radiation after TORS and quantified non-targeted primary site dose.
Methods:
Following IRB approval, patients treated with primary TORS resection for squamous cell carcinomas of the oropharynx were reviewed. Patients with cT1-2 tumors, >2 mm margins, in whom the surgeon resected the primary without revising specimen-driven margins, qualified for omission of primary site radiation.
Results:
From 2014 to 2019, 112 patients met criteria. Fifty-nine (52%) patients did not receive radiation targeting the primary site of whom 22 received no radiation. In this group, there were no local failures; mean age was 58 years and median follow-up was 25 months. Thirty-seven patients received adjuvant radiation targeting the neck, mean bystander dose to the primary site was 28.8 Gy (range 13.3-50.6 Gy).
Conclusions:
In a 59 patient population omission of radiation to the primary site after TORS resulted in no loco-regional failures.
Introduction
The treatment of the oropharyngeal squamous cell carcinomas (OPSCC) has continued to evolve over the past decade. Classically treated with surgical resection, difficulties with exposure of the primary oropharyngeal sites led to long-term functional deficits. This paradigm shifted in the 1970s with the advent of radiation that offered favorable control rates with reduced morbidity.[1] With the addition of concurrent chemotherapy in the 1990s the disease specific control using radiation significantly improved, establishing a new standard of care. [2]
As a favorable subset of oncogenic human papillomavirus (HPV) driven OPSCC was recognized, trials have investigated treatment de-escalation through reduction in radiation dose, alternative treatment volumes, and modification of chemotherapy with mixed results. [3]
Transoral robotic surgery (TORS) enabled 3-D magnified visualization and improved access to oropharyngeal sites. By substantially decreasing morbidity (i.e. avoiding mandibulotomy) of traditional surgical approaches to the oropharynx, TORS re-introduced surgery as a viable pathway in management of selected OPSCC patients. Excellent results were seen with local control rates exceeding 90%. [4, 5]
Based on favorable locoregional control rates following TORS, our institution implemented a policy of omitting intentional primary site radiation after definitive trans-oral robotic surgery (TORS) surgery in a selected, low-risk population. We sought to investigate if omission of intentional primary site radiation was detrimental to local or regional control. Here, we present the results of this single institution experience and our analysis includes a review of unintended, “bystander” radiation to the primary site.
Materials and Methods
We conducted an IRB approved (IRB#104979) retrospective review of adult patients with primary OPSCC who underwent TORS from 2014 to 2019. Institutionally, TORS has been offered to patients with clinical T1-2 tumors. Radiation volume decisions, however, were based on pathologic findings. Thus, patients who were not upstaged on final pathology were eligible for omission of primary site radiation (i.e. patients who had pathologic T1-2 tumors). At minimum, all patients had radiation treatment summaries (with detail of primary site treatment and dose) available for review. Patients were excluded if they received prior head and neck radiation or chemotherapy prior to surgery. We discussed omission of primary site radiation with each patient and offered each patient the option of receiving primary site radiation. None requested primary site radiation once the radiation oncologist and surgeon agreed that it was not necessary.
TORS oropharyngectomy was designed to achieve ≥3 mm mucosal margins with the deep margin consisting of the constrictor muscle deep to the tonsil as well as the styloglossus and stylopharyngeus muscles. The inferior margin of a TORS palatine tonsillectomy includes a small amount of lingual tonsil and the superior margin cut is just lateral to the uvula. TORS tongue base resection incision is made along the circumvallate papillae ipsilateral to the tumor to include the intrinsic tongue musculature. The maximal depth of resection was to the lingual artery and hyoid bone. The posterior mucosal cut was along the mucosa covering the epiglottis. Pathological margins were evaluated from the specimen at the time of resection with the use of frozen section.
After discussion between the treating head and neck surgeon and radiation oncologist, a post-op radiation treatment plan was designed and adjuvant radiation to the primary was omitted if the deep margin and mucosal margins were > 2 mm and both physicians were comfortable with omission. Transiently positive margins, even if revised to negative, were a contraindication for omission of radiation to the primary site. Concurrent chemotherapy was incorporated for extra-nodal extension (ENE), regardless of extent. Lymphovascular invasion, PNI and pathological nodal status were not contraindications to omitting primary site adjuvant radiation. In most cases, LVI and PNI were consequential when they were identified on frozen section in the context of transiently positive margins. There was no consideration of bystander dose contribution when assessing necessity of radiation to the primary site.
Radiation, when administered, was delivered to either the ipsilateral or bilateral neck based on primary tumor location, extent, and size and based on nodal disease burden. Patients underwent CT simulation after thermoplastic mask immobilization and 3-dimensional target volumes were delineated. High risk clinical target volumes (CTV) included regions of ENE and were prescribed 63-66 Gray (Gy). Intermediate risk CTV included the ipsilateral dissected neck and received 50-60 Gy. The low risk CTV included the contralateral uninvolved and undissected neck and was prescribed 50-54 Gy. The population (post-TORS OPSCC) included patients enrolled on national clinical trials (such as ECOG 3311) where lower doses were specified. All patients treated on clinical trials received intentional primary site radiation and were assessed in the control group.
Decisions about treatment of the primary site irradiation were addressed above. Preoperative positron emission tomography/CT (PET/CT) scans were fused to CT simulation scans to guide radiation volumes. Patients were treated using either linear accelerator based volumetric modulated arc therapy (VMAT) or, for one patient, pencil beam scanning proton therapy. Three-millimeter planning volume expansions were used for photon treated patients to account for setup uncertainty. Daily on-board imaging with kV/kV films was employed for matching. Cone-beam CT scans were used at provider discretion.
For the patients in whom intentional primary site radiation was omitted, primary site target volumes were retroactively contoured by fusion of the pre-operative tumor volume as defined by preoperative PET/CT, with additional 5 mm anatomically appropriate margin to create a clinical target volume (Figure 2). This mirrors the practice for patients in whom the primary site received targeted radiation. Only patients that received adjuvant radiation were included in comparisons of bystander dose and mean oral cavity dose. Pathology reports were reviewed for tumor stage, tumor size, nodal dissection and extra-nodal extension (ENE), lymphovascular invasion (LVI), and perineural invasion (PNI).
Figure 2:
Representative images demonstrating operative bed delineation in a patient with (i) left tonsil primary tumor without intentional primary site targeting and (ii) left base of tongue primary tumor with intentional primary site targeting. Operative bed is delineated in pink and CTV_6000 is delineated in red. Isodose levels include 60Gy (yellow) and 54Gy (blue).
Descriptive statistics were utilized for patient demographics, clinical characteristics, specimen and staging data, and follow-up. Continuous features were summarized with means, medians, standard deviations, and ranges. We additionally assessed radiation dose to various volumes including mean volume receiving 60Gy, 50Gy, and 40 Gy (V60Gy, V50Gy, and V40Gy, respectively). These volumes represent the average volume receiving prescription dose (V60Gy), intermediate dose (V50Gy) and less than intermediate dose (V40Gy).
Results
We identified 112 patients that fulfilled study criteria and were included in further analysis. Fifty-nine (52%) patients did not receive intentional radiation to the primary site. One patient received proton-based treatment while the remainder received photon-based IMRT using VMAT. One hundred and nine (97%) patients were HPV+. Median age was 58.5 years for the entire cohort (IQR 1,3 52-64 years).
Among the omission cohort (Table 2), there were 29 (49%) tonsillar, 27 (46%) base of tongue and 3 (5%) soft palate tumors. Mean age at diagnosis was 58 years and 88% of patients were male. Median follow-up was 25 months for the omission cohort (Table 3) with 23 (49%) patients in the omission cohort having follow-up ≥3 years and 34 (58%) having follow-up ≥2 years. Thirty-seven (63%) patients were T1, 12 (21%) N0, 43 (74%) N1, and 1 (2%) patient was N2. Median tumor size was 1.6 cm (0.3 – 3.8) and median margin was 4 mm. There were 17 (28%) cases with LVI, 2 (3%) with PNI and 16 (28%) with ENE. Mean distance to margin was significantly greater for patients with omission of primary site radiation (4.5mm vs 3.1mm for omission vs. control, respectively, p=0.008)
Table 2:
Characteristics of Patients Without Intentional Primary Site Targeting
| Subsite | Tonsil | Base of Tongue |
Soft Palate* | Total (% of total) |
|---|---|---|---|---|
| N (% of total) | 29 (49%) | 27 (46%) | 3 (5%) | 59 (100%) |
| AJCC 8 Stage I (% of subsite) | 29 (100%) | 25 (93%) | 3(100%) | 57 (97%) |
| Neck RT (% of subsite) | 13 (45%) | 23 (85%) | 0 | 36 (61%) |
| Bilateral neck RT (% of subsite) | 9 (31%) | 18 (67%) | 0 | 27 (47%) |
Breakdown of primary site omission cohort detailing pathologic staging, any neck radiation, or bilateral neck radiation. Twenty-two patients in the cohort received no radiation and one patient was treated at an outside institution without specification of nodal levels of treatment leaving 36 patients who received adjuvant radiation.
No patients with soft palate primary tumors received adjuvant radiation.
Table 3-.
Radiation Cohort Comparisons
| RT primary |
|||||
|---|---|---|---|---|---|
| Covariate | Statistics | Level | No N=59 | Yes N=53 | P-value* |
| Sex | N (Col %) | Female | 7 (11.86) | 6 (11.32) | 0.929 |
| N (Col %) | Male | 52 (88.14) | 47 (88.68) | ||
| Race | N (Col %) | Caucasian | 53 (89.83) | 49 (92.45) | 0.746 |
| N (Col %) | African American | 6 (10.17) | 4 (7.55) | ||
| Tumor Subsite | N (Col %) | Tonsil | 29 (49.15) | 29 (54.72) | 0.337 |
| N (Col %) | Base of tongue | 27 (45.76) | 24 (45.28) | ||
| N (Col %) | Soft palate | 3 (5.08) | 0 (0) | ||
| PNI | N (Col %) | No | 57 (96.61) | 42 (79.25) | 0.004 |
| N (Col %) | Yes | 2 (3.39) | 11 (20.75) | ||
| LVI | N (Col %) | No | 42 (71.19) | 31 (58.49) | 0.159 |
| N (Col %) | Yes | 17 (28.81) | 22 (41.51) | ||
| ENE | N (Col %) | No | 42 (71.19) | 33 (62.26) | 0.316 |
| N (Col %) | Yes | 17 (28.81) | 20 (37.74) | ||
| Concurrent chemotherapy | N (Col %) | No | 44 (74.58) | 36 (67.92) | 0.437 |
| N (Col %) | Yes | 15 (25.42) | 17 (32.08) | ||
| Chemotherapy regimen | N (Col %) | Cisplatin | 13 (92.86) | 15 (88.24) | 1.000 |
| N (Col %) | Carboplatin Paclitaxel | 1 (7.14) | 2 (11.76) | ||
| Age at surgery (years) | N | 59 | 53 | 0.934 | |
| Mean | 58.41 | 58.55 | |||
| Median | 59 | 57 | |||
| Distance to margin (mm) | N | 47 | 48 | 0.008 | |
| Mean | 4.5 | 3.03 | |||
| Median | 4 | 2 | |||
| Total RT duration (days) | N | 37 | 53 | 0.514 | |
| Mean | 43.08 | 42.4 | |||
| Median | 42 | 43 | |||
| Oral cavity dose (Gy) | N | 35 | 42 | 0.004 | |
| Mean | 26.03 | 30.51 | |||
| Median | 26.5 | 29.1 | |||
| Follow-up time (months) | N | 59 | 53 | 0.087 | |
| Mean | 28.31 | 23.34 | |||
| Median | 25 | 22 | |||
The p-value is calculated by ANOVA for numerical covariates; and chi-square test or Fisher's exact for categorical covariates, where appropriate.
Of the 59 omission patients, 22 (40%) received no adjuvant radiation, 10 (17%) received radiation to the ipsilateral neck alone and 27 (46%) received radiation to the bilateral neck. The group that did not receive any radiation was comprised of 13 patients with T1-2N0 cancers of any primary site (including all 3 patients with tumors of the soft palate), 6 with T1N1 tonsil or tongue base cancer, and 3 with T2N1 tonsil cancer.
For the 53 patients who received radiation to the primary tumor site, the indications for intentionally targeting the primary site were ≤2 mm margins for 43%, clinical trial protocol for 23%, T3/T4 tumors for 4%, and for 30% other indications such as transiently positive margins or PNI. Thirty-one patients (28%) received concurrent chemotherapy due to the presence of ENE, 15 (25%) in the omission group and 16 (32%) in the non-omission group.
Among patients who received primary site radiation, one local and one regional failure were seen. One local recurrence was confirmed 24 months after TORS oropharyngectomy for p16+ tonsil primary following adjuvant CRT to primary site and bilateral neck. Pertinent history included HIV, advanced primary tumor stage, and ENE. The patient was initially staged clinically as T2 tonsil cancer, however, by the time of surgery developed trismus and was confirmed on final pathology to have T4 disease. The one regional recurrence was confirmed, in the contralateral non-radiated neck of a T2N1 tonsillar patient with ENE treated at an outside hospital, 18 months after completion of treatment. In the omission cohort, there were no local or regional failures, with one patient developing distant metastasis.
Amongst the omission cohort, mean unintentional dose to the PET/CT defined primary site plus 5 mm margin volume was 28.8 Gy (range 13.3-50.6 Gy). Mean volume receiving 60Gy, 50Gy, and 40Gy (V60Gy, V50Gy, V40Gy) was 42.6% (range 2.80%-95.6%), 73.2% (range 26.3%-100%), and 87.4% (range 36.7%-100%), respectively. Mean oral cavity dose was significantly decreased in patients without intentional primary site radiation (26.0 Gy vs 30.5 Gy, p=0.004).
There was no significant difference between unilateral vs. bilateral neck treatment (levels II-IV) between the omission and non-omission cohorts (p=0.76). Additionally, there was no significant difference in mean dose to the ipsilateral parotid gland (p=0.606), contralateral parotid gland (p=0.517), larynx (p=0.650), or superior pharyngeal constrictors (p=0.792). Dose to the pharyngeal constrictors was inconsistently reported, especially in patients with treatment of the ipsilateral or contralateral retropharyngeal nodes. Significantly more patients in the omission cohort received treatment to the ipsilateral level Ib and ipsilateral and/or contralateral retropharyngeal nodes (Table 4).
Table 4 -.
RT primary comparisons
| RT primary |
|||||
|---|---|---|---|---|---|
| Covariate | Statistics | Level | No N=59 | Yes N=53 | P-value* |
| Neck treatment† | N (Col%) | Unilateral | 8 (22.22) | 13 (25) | 0.76 |
| Bilateral | 28 (77.78) | 39 (75) | |||
| Ipsilateral 1b | N (Col %) | Untx | 5 (13.89) ‡ | 13 (27.66) § | 0.032 |
| N (Col %) | >=60Gy | 25 (69.44) | 19 (40.43) | ||
| N (Col %) | <60Gy | 6 (16.67) | 15 (31.91) | ||
| Contralateral 1b | N (Col %) | Untx | 36 (100) ‡ | 46 (97.87) § | 1.000 |
| N (Col %) | >=60Gy | 0 (0) | 1 (2.13) | ||
| Ipsilateral RP | N (Col %) | Untx | 0 (0) ‡ | 7 (14.89) § | 0.041 |
| N (Col %) | >=60Gy | 10 (27.78) | 13 (27.66) | ||
| N (Col %) | <60Gy | 26 (72.22) | 27 (57.45) | ||
| Contralateral RP | N (Col %) | Untx | 17 (47.22) ‡ | 32 (68.09) § | 0.043 |
| N (Col %) | >=60Gy | 0 (0) | 1 (2.13) | ||
| N (Col %) | <60Gy | 19 (52.78) | 14 (29.79) | ||
| Max acute tox (mucositis/dysphagia) | N (Col %) | 0 | 1 (2.78) ‡ | 1 (2.13) § | 0.980 |
| N (Col %) | 1 | 14 (38.89) | 17 (36.17) | ||
| N (Col %) | 2 | 12 (33.33) | 17 (36.17) | ||
| N (Col %) | 3 | 9 (25) | 12 (25.53) | ||
| Feeding tube | N (Col %) | No | 29 (78.38) | 38 (79.17) | 0.930 |
| N (Col %) | Yes | 8 (21.62) | 10 (20.83) | ||
| Parotid ipsilateral (Gy) | N | 36‡ | 46 | 0.606 | |
| Mean | 31.2 | 30.26 | |||
| Median | 28.35 | 28.3 | |||
| Parotid contralateral (Gy) | N | 36‡ | 46 | 0.517 | |
| Mean | 17.32 | 18.36 | |||
| Median | 20.15 | 21.4 | |||
| Larynx (Gy) | N | 36‡ | 46 | 0.650 | |
| Mean | 31.11 | 32.07 | |||
| Median | 32.45 | 33.65 | |||
| Superior pharyngeal constrictors (Gy) | N | 5 | 31 | 0.792 | |
| Mean | 43.24 | 41.74 | |||
| Median | 50.1 | 43.3 | |||
| PEG duration (days) | N | 8 | 10 | 0.590 | |
| Mean | 122.88 | 146.2 | |||
| Median | 112.5 | 117 | |||
The p-value is calculated by ANOVA for numerical covariates; and chi-square test or Fisher's exact for categorical covariates, where appropriate
Comparison of omission and non-omission cohorts demonstrating nodal levels treated, dose to organs at risk (OARs), max mucositis grade (provider assessed), PEG-tube insertion, and PEG tube duration.
Bilateral neck treatment only relates to treatment of nodal levels II-IV.
One patient was treated at an outside institution and did not have nodal levels specified and 22 received no radiation, leaving a population of 36 for analysis.
Six patients were treated at outside institutions and did not have OAR doses or specific nodal level details available, one patient had previously been treated for a glomus tumor and only received primary site radiation, leaving a population of 47 patients for analysis.
Toxicity, including maximum provider-assessed mucositis grade and percutaneous gastrostomy tube (PEG) insertion and duration, was similar between the two cohorts. Doses to the ipsilateral parotid gland and larynx were associated with increased risk of PEG tube insertion but not duration (supplemental S1a,b). When stratifying by treatment of primary site the association between ipsilateral parotid gland dose and feeding tube insertion was no longer significant (p=0.08 and p=0.24 for omission and non-omission cohorts, respectively) due to the smaller sample sizes.
Discussion
Omission of intentional primary site radiation in an appropriately selected population of OPSCC resulted in no local-regional treatment failures and significantly reduced mean oral cavity dose in a sizeable single-institution cohort with median follow-up of 25 months. In contrast to prior reports[6] patients with PNI and LVI were potentially eligible for omission of primary site radiation and did not experience increased risk of locoregional recurrence. Control rates in both study cohorts compare favorably to other published studies ([6-9]) and all observed treatment failures were in high risk patients.
Recently, the results of the single arm Phase II AVOID trial were released. This is the largest study to date that prospectively investigated omission of primary site radiation in a low risk (pT1-2; N0-3) cohort without lymphovascular invasion (LVI) or perineural invasion (PNI) and reported a 98.3% control rate for the primary site[6]. In agreement with the publication by Swisher-McClure et al., we observed a significant decrease in mean oral cavity dose with omission of primary site radiation. Notably, nearly all patients in our study were treated with VMAT, in comparison to 50% of patients receiving protons in the AVOID trial. [6] The AVOID trial also electively treated both necks, whereas a substantial portion of our patients received unilateral neck radiation. Additionally, most patients in our study received photon-based radiotherapy. The majority of either definitive, adjuvant, or salvage radiotherapy to the head and neck is performed with photon-based radiation treatments. In contrast to proton therapy, which limits dose to surrounding tissues, photon-based intensity-modulated radiotherapy inherently produces a “dose-wash” where low-dose radiation is spread over a large volume to allow a central, concentrated, high-dose region.
First line treatment strategy for early stage OPSCC remains controversial. Nichols et al. recently reported a randomized trial documenting a statistically significant but clinically not meaningful improvement in swallowing related quality of life (QOL) scores at 1 year with radiation compared to TORS. [10] In contrast, retrospective reports from Sharma et al., and Pasalic et al, demonstrated a significant increase in adverse effects with CRT compared to primary TORS.[11, 12]
Contreras et al. reported no isolated regional failures with omission of postoperative radiation to the pathologically node negative neck [13]. Our data support omission of intentional radiation to both the primary site and neck in a population of patients with T1-2, N0, and selected N1 cases of OPSCC following primary TORS resection. Of the 22 patients that received no adjuvant radiation, no failures were recorded.
In addition to problems inherent in a retrospective analysis, such as selection bias, unintentional primary site radiation remains the major limitation of our study. In patients without intentional primary site radiation, operative bed V40Gy, which represents the volume of tissue treated to a dose of 40Gy, was 87%, which may be sufficient to control microscopic disease. This could be further investigated through protocols that aggressively avoid primary site radiation.[14, 15]. The increased utilization of TORS in academic versus community practices also limits the generalizability of our data [16].
Importantly, there is a lack of standardized risk stratification for TORS patients. We defined our low risk cohort as patients with pT1-pT2 oropharyngeal tumors, without transiently positive margins, and final margins > 2 mm. Weinstein et al. and Swisher-McClure et al. reported a close margin as ≤ 2 mm, and a negative margin >2 mm and did not specifically consider a transiently positive margin [6, 7]. The impact of HPV status on these risk criteria remains unanswered.
While attempts to reduce morbidity through alteration of concurrent systemic therapy regimens have largely been unsuccessful [3] [17], alteration of radiation dose or schedule remains a promising avenue for exploration as demonstrated in MC1273[18]. We eagerly await the results of radiation dose de-intensification trials such as ECOG 3311, ADEPT, and PATHOS.
Supplementary Material
Figure 1-.
Local control
Table 1 -.
Descriptive Statistics - Patient characteristics
| Variable | Level | N = 112 | % |
|---|---|---|---|
| Sex | Female | 13 | 11.6 |
| Male | 99 | 88.4 | |
| Race | Caucasian | 102 | 91.1 |
| African American | 10 | 8.9 | |
| Tumor Subsite | Tonsil | 58 | 51.8 |
| Base of tongue | 51 | 45.5 | |
| Soft palate | 3 | 2.7 | |
| Neck dissection | Yes | 112 | 100.0 |
| Margin Status | Negative | 112 | 100.0 |
| PNI | No | 99 | 88.4 |
| Yes | 13 | 11.6 | |
| LVI | No | 73 | 65.2 |
| Yes | 39 | 34.8 | |
| ENE | No | 75 | 67.0 |
| Yes | 37 | 33.0 | |
| RT primary | No | 59 | 52.7 |
| Yes | 53 | 47.3 | |
| RT primary dose (Gy) | 50 | 8 | 15.1 |
| 54 | 1 | 1.9 | |
| 60 | 35 | 66.0 | |
| 63 | 3 | 5.7 | |
| 66 | 5 | 9.4 | |
| 70 | 1 | 1.9 | |
| N/A | 59 | - | |
| Concurrent chemotherapy | No | 80 | 71.4 |
| Yes | 32 | 28.6 | |
| Chemotherapy regimen | Cisplatin | 28 | 90.3 |
| Carboplatin Paclitaxel | 3 | 9.7 | |
| N/A | 81 | - | |
| Age at surgery (years) | Mean | 58.47 | - |
| Median | 58.50 | - | |
| Minimum | 38 | - | |
| Maximum | 93 | - | |
| Std Dev | 8.93 | - | |
| Distance to margin (mm) | Mean | 3.76 | - |
| Median | 3 | - | |
| Minimum | 0.40 | - | |
| Maximum | 15 | - | |
| Std Dev | 2.74 | - | |
| Missing | 17 | - | |
| Total RT duration (days) | Mean | 42.68 | - |
| Median | 43 | - | |
| Minimum | 30 | - | |
| Maximum | 55 | - | |
| Std Dev | 4.87 | - | |
| N/A | 22 | - | |
| V60Gy(%)* | Mean | 42.55 | - |
| Median | 39.10 | - | |
| Minimum | 2.80 | - | |
| Maximum | 95.60 | - | |
| Std Dev | 24.11 | - | |
| N/A | 78 | - | |
| V50Gy(%)* | Mean | 73.20 | - |
| Median | 78.75 | - | |
| Minimum | 26.30 | - | |
| Maximum | 100 | - | |
| Std Dev | 18.96 | - | |
| N/A | 78 | - | |
| V40Gy(%)* | Mean | 87.39 | - |
| Median | 93.85 | - | |
| Minimum | 36.70 | - | |
| Maximum | 100 | - | |
| Std Dev | 16.73 | - | |
| N/A | 78 | - | |
| D100%(Gy)* | Mean | 28.78 | - |
| Median | 29.25 | - | |
| Minimum | 13.30 | - | |
| Maximum | 50.60 | - | |
| Std Dev | 9.80 | - | |
| N/A | 78 | - | |
| Primary Mean (Gy)* | Mean | 54.29 | - |
| Median | 55.45 | - | |
| Minimum | 38.80 | - | |
| Maximum | 63.10 | - | |
| Std Dev | 5.62 | - |
Only patients in the primary site omission cohort considered for calculation
Acknowledgments
Research reported in this publication was supported in part by the Biostatistics Shared Resource of Winship Cancer Institute of Emory University and NIH/NCI under award number P30CA138292. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
Footnotes
Conflicts of interest: The authors have no pertinent conflicts of interest
This work was an oral presentation at the 2019 AHNS Annual Meeting
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