Abstract
Background
The contribution of high radiation dose outliers to cumulative occupational radiation dose is understudied.
Methods
Physician radiation data were collected during consecutive coronary cases, and per case doses were ranked by magnitude. The relationship between the per case rank and relative contribution to cumulative dose was summed for cases ≤50th percentile and for cases >90th percentile. A similar methodology was applied for radiation doses among structural interventionalists, interventional echocardiographers, scrub technologists, and nurse circulators. Multivariable logistic regression was fit to identify independent predictors of physician radiation dose >90th percentile during coronary cases.
Results
Across 363 coronary cases, the median physician radiation dose per case was 10.2 (3.2, 35.5) μSv, and the cumulative radiation dose was 13,230 μSv. Coronary cases ≤50th percentile accounted for only 5.0% of the cumulative radiation dose. Cases >90th percentile accounted for 60.3% of the cumulative dose. Cases >90th percentile accounted for 51.3%, 39.9%, 45.8%, and 64.8% of the cumulative dose among structural interventionalists, interventional echocardiographers, scrub technologists, and nurse circulators, respectively. ST-segment elevation myocardial infarction (OR, 6.2; 95% CI, 1.5-26.3; P = .01), percutaneous coronary intervention (OR, 5.6; 95% CI, 2.2-14.2; P < .001), right heart catheterization (OR, 4.4; 95% CI, 1.7-11.7; P = .003), and male sex (OR, 3.2; 95% CI, 1.3-8.0; P = .01) were independently associated with physician radiation dose >90th percentile.
Conclusions
Physician radiation dose outliers contribute disproportionately to the cumulative radiation dose, with cases above the 90th percentile accounting for 60% of the cumulative dose. High radiation dose outliers are an important target for future radiation mitigation efforts.
Keywords: cardiac catheterization, catheterization laboratory, radiation safety
Introduction
The risks of radiation exposure are postulated to increase with lifetime radiation dose, thereby making cumulative radiation dose an important metric when considering occupational risk. The importance of cumulative radiation dose has been highlighted by recent evidence demonstrating its association with various hematologic malignancies.1 In addition to concerns about cancer, cumulative radiation dose is also thought to contribute to the occupational risk of developing premature cataracts among physicians and staff working in the cardiac catheterization laboratory.2 Owing to these occupational risks, efforts to reduce radiation exposure among physicians and staff have recently been highlighted as a moral imperative.3
Contemporary studies of radiation exposure in the catheterization laboratory often evaluate occupational risk by reporting the average radiation doses per case to which physicians or staff members are exposed.4, 5, 6 Because the distribution of radiation doses is frequently skewed, average radiation doses are most commonly reported as median doses. However, the median radiation dose may not properly weigh rare cases in which extremely high operator radiation doses are observed. Such outlier cases can disproportionately contribute to cumulative radiation dose and may be driving much of the occupational radiation exposure risk, yet they remain understudied. The present study was performed to examine the relative contribution of high radiation dose outliers on the cumulative radiation dose among physicians performing coronary angiography. To determine if the impact of high-dose outliers observed among physicians performing coronary cases was also observed among other roles in the catheterization laboratory, this study evaluated the relative contribution of high radiation dose outliers on the cumulative radiation dose among structural interventionalists, interventional echocardiographers, scrub technologists, and circulating nurses.
Materials and methods
This study was a single-center prospective observational study designed to investigate the radiation exposure of physicians and staff members in the cardiac catheterization laboratory. This study (the methodology of which has been previously published4,7,8) was conceived, designed, and conducted by investigators at Corewell Health. The local institutional review board approved the protocol and provided a waiver of consent for patients. All physicians and staff members participating in the study provided informed consent. The data were housed at the study institution, and investigators had full access to the data for analysis. The principal investigator of the study (R.D.M.) takes responsibility for the study integrity and data analysis. Upon reasonable request and with appropriate funding, the data, analytic methods, and materials for this study will be made available to other researchers for purposes of reproducing the results.
Selection of the study population
Between August 2015 and February 2016, data on coronary cases were prospectively collected on consecutive procedures performed in 2 fluoroscopy suites having identical fluoroscopy systems (Allura Xper FD10 X-ray system, Philips). All cases having a start time between approximately 8 o’clock am and 5 o’clock pm, Monday through Friday, were included in the study. Cases that did not utilize any radiation were excluded as specified in the study protocol. For the purposes of analyzing radiation doses in coronary procedures, only those procedures in which coronary angiography was performed were included in the primary analyses. Cases in which the physician did not wear a real-time dosimeter during the case were excluded from analysis. Owing to the superior radiation protection provided by a suspended lead suit or a robotic system compared to conventional lead aprons,4,9 cases performed with robotics or in which the physician utilized a suspended lead suit for part or all of the case were excluded.
To determine if the impact of high-dose outliers observed among physicians performing coronary cases was also observed among other roles in the catheterization laboratory, radiation doses among scrub technologists and circulating nurses were collected from the same database as described above.7 Separate analyses were conducted to determine the impact of high radiation dose outliers among interventional echocardiographers and structural interventionalists using a previously published cohort of 30 consecutive mitral transcatheter edge-to-edge repair and 30 consecutive left atrial appendage occlusion cases conducted between July 2016 and January 2018.10 The data collected on structural cases between 2016 and 2018 were a subsequent phase of the same study described above in which data were collected on coronary cases between 2015 and 2016.
Radiation monitoring
For all cases, real-time radiation exposure data were collected using a commercially available dosimetry system that contains a bedside monitor capable of displaying real-time radiation doses (RaySafe i2, Unfors RaySafe). Physicians and staff members were blinded to the monitor display and to the radiation data collected by the dosimeters for the duration of the study to minimize changes to practice patterns. During the study, each physician and staff member wore a dosimeter located on either the left anterior side of the glasses or on the left anterior side of the thyroid collar as previously described.4,7,8,10 Standard settings at the study institution included a frame rate of 7.5 frames/s for fluoroscopy and 15 frames/s for cineangiography.
Radiation protection
For personal protection in each case, physicians and staff members wore conventional lead aprons and a thyroid collar. According to institutional standards, 2 shields were positioned between the patient and interventional cardiologist in all cases: a ceiling-mounted upper body lead shield with a patient contour cutout and a lower body lead shield attached to the side of the operating table extending from the table to the floor. For structural interventions, the interventional echocardiographer utilized a mobile, height-adjustable, accessory lead shield (Mobile Shield WD257, Mavig).10 This shield was positioned between the patient and the interventional echocardiographer. The lower section of this shield (width, 78 cm; height, 95 cm) is comprised of a nontransparent steel body, which is not height-adjustable, has a lead equivalency of 1.0 mm Pb, and is intended to protect the lower body of the health care provider from scatter radiation. The upper section of this shield (width, 70 cm), which is height-adjustable, consists of a transparent lead acrylic panel having a lead equivalency of 0.5 mm Pb. The upper section of the shield was raised to a height that allowed the interventional echocardiographers to extend their arms over the shield to manipulate the transesophageal echocardiography probe throughout the case. For all cases, a radiation-absorbing disposable pad (RadPad, Worldwide Innovations & Technologies) was utilized at the discretion of the operating physician and staff members.
Radiation dose metrics
Individual physician and staff member radiation doses were measured for each case. The dose per case was the personal dose equivalent, Hp(10), as recorded and reported directly by the dosimetry system. Secondary measures of interest included other radiation metrics, including the fluoroscopy time, air kerma (AK), and dose area product (DAP), which were automatically calculated by the fluoroscopy imaging system.
Statistical analysis
To understand the relative contribution of high radiation dose outliers to the cumulative radiation dose, physician radiation doses per case were ranked by magnitude from least to greatest. The relative contribution of the per case radiation dose to the cumulative radiation dose was summed for cases using the following categories: ≤50th percentile, 51st to 75th percentiles, 76th to 90th percentiles, 91st to 95th percentiles, 96th to 99th percentiles, and >99th percentile. Similar methodology was applied to explore radiation doses for structural interventionalists, interventional echocardiographers, scrub technologists, and circulating nurses as above.
P values for comparison of physician radiation doses among coronary angiography cases with and without percutaneous coronary intervention (PCI) were derived from Wilcoxon rank sum tests because radiation doses were not normally distributed. P values for comparisons of variables above and below the 90th percentile of physician radiation dose were derived from 2-sample independent t tests for continuous variables that were normally distributed or from Wilcoxon rank sum tests for continuous variables that were not normally distributed. P values for comparison of categorical variables among cases above and below the 90th percentile of physician radiation dose were generated with a χ2 analysis or a Fisher exact test if the expected cell counts were <5 in >20% of the cells.
A multivariable logistic regression model was fit to identify independent predictors of cases in which physician radiation dose exceeded the 90th percentile during coronary angiography. Results of univariate comparisons were evaluated to select variables for the model. Variables having a P value <.15 in univariate comparisons were included in the final model. The final model used backward selection, although no variables were removed. Thus, the final model included patient sex, PCI, right heart catheterization (RHC), and ST-segment elevation myocardial infarction (STEMI).
Normally distributed continuous variables are shown as mean ± SD. Nonnormally distributed continuous variables are shown as median (IQR). Categorical variables are shown as count (%). All statistical analyses were generated using SAS version 7.1 (SAS Institute).
Results
A total of 1119 cases, performed by a total of 26 physicians, were included in the registry. After excluding 16 cases in which the physician did not wear a dosimeter and 739 cases in which either a suspended lead suit or robotic system was used, 363 cases in which the operating physician performed coronary angiography and wore conventional lead aprons were included in the present analysis. Patient characteristics and procedural details for the study population are shown in Table 1. Adjunctive procedures included RHC in 23.4% of cases, fractional flow reserve in 14.3%, and PCI in 34.2%. Cases were characterized by a fluoroscopy time of 6.1 (3.4-11.6) minutes, AK 771 (538-1211) mGy, and DAP 64.6 (42.9-96.9) Gy·cm2.
Table 1.
Patient and procedural characteristics of the study population.
| Characteristic | N = 363 |
|---|---|
| Age, y | 68.0 ± 11.7 |
| Body mass index, kg/m2 | 31.0 ± 7.0 |
| Male sex | 217 (59.8) |
| Arterial access | |
| Femoral | 216 (59.5) |
| Radial/brachial | 147 (40.5) |
| Fractional flow reserve | 52 (14.3) |
| Percutaneous coronary intervention | 124 (34.2) |
| Right heart catheterization | 85 (23.4) |
| Radiation-absorbing pad | 138 (38.6) |
| ST-segment elevation myocardial infarction | 10 (2.8) |
| Radiation metrics | |
| Fluoroscopy time, min | 6.1 (3.4-11.6) |
| Air kerma, mGy | 771 (538-1211) |
| Dose area product, Gy·cm2 | 64.6 (42.9-96.9) |
Age and body mass index are shown as mean ± SD. Radiation metrics are shown as median (IQR). All other values are the number (%).
Per case relative contribution to cumulative radiation dose
Across the 363 coronary angiography cases, the cumulative radiation dose among physicians was 13,230 μSv. Physicians had a median radiation dose per case of 10.2 (3.2-35.5) μSv. Physician radiation dose was higher among cases with PCI (14.3 [5.9-57.2] μSv) compared to cases in which diagnostic coronary angiography was performed without PCI (7.1 [2.4-26.7] μSv; P < .001).
The relationship between the per case physician radiation dose and the cumulative dose for all coronary cases is shown in the Central Illustration and Table 2 and is displayed as the percentile rank and relative contribution to the cumulative radiation dose. Cases ≤50th percentile accounted for only 5.0% of the cumulative radiation dose across all 363 cases. The 36 cases above the 90th percentile accounted for 60.3% of the cumulative radiation dose, whereas the 3 cases above the 99th percentile accounted for 19.0% of the cumulative radiation dose.
Central Illustration.
Relative contribution of high-dose outliers to cumulative occupational radiation dose in the catheterization laboratory. CN, circulating nurse; IC, interventional cardiologist; IE, interventional echocardiographer; SI, structural interventionalist; ST, scrub technologist.
Table 2.
Per case radiation dose percentile rank and contribution to the cumulative radiation dose.
| Per-case radiation dose percentile rank | n | Cumulative radiation dose (μSv) | % Contribution to cumulative radiation dose |
|---|---|---|---|
| Interventional cardiologist—coronary cases | |||
| All cases | 363 | 13,230 | 100% |
| ≤50th percentile | 183 | 659.1 | 5.0% |
| 51st to 75th percentile | 90 | 1720.6 | 13.0% |
| 76th to 90th percentile | 54 | 2872.9 | 21.7% |
| 91st to 95th percentile | 18 | 2060.9 | 15.6% |
| 96th to 99th percentile | 15 | 3403.8 | 25.7% |
| >99th percentile | 3 | 2512.7 | 19.0% |
| Structural interventionalist | |||
| All cases | 60 | 1361.0 | 100% |
| ≤50th percentile | 30 | 139.3 | 10.2% |
| 51st to 75th percentile | 15 | 249.2 | 18.3% |
| 76th to 90th percentile | 9 | 275.0 | 20.2% |
| 91st to 95th percentile | 3 | 132.2 | 9.7% |
| 96th to 99th percentile | 2 | 222.7 | 16.4% |
| >99th percentile | 1 | 342.5 | 25.2% |
| Interventional echocardiographer | |||
| All cases | 60 | 308.5 | 100% |
| ≤50th percentile | 29 | 17.3 | 5.6% |
| 51st to 75th percentile | 16 | 69.4 | 22.5% |
| 76th to 90th percentile | 9 | 98.4 | 31.9% |
| 91st to 95th percentile | 3 | 48.1 | 15.6% |
| 96th to 99th percentile | 2 | 42.1 | 13.6% |
| >99th percentile | 1 | 33.1 | 10.7% |
| Scrub technologist | |||
| All cases | 604 | 1232.9 | 100% |
| ≤50th percentile | 313 | 112.3 | 9.1% |
| 51st to 75th percentile | 143 | 231.6 | 18.8% |
| 76th to 90th percentile | 88 | 324.9 | 26.4% |
| 91st to 95th percentile | 32 | 214.2 | 17.4% |
| 96th to 99th percentile | 22 | 228.4 | 18.5% |
| >99th percentile | 6 | 121.5 | 9.9% |
| Circulating nurse | |||
| All cases | 629 | 1454.6 | 100% |
| ≤50th percentile | 322 | 43.4 | 3.0% |
| 51st to 75th percentile | 155 | 177.4 | 12.2% |
| 76th to 90th percentile | 91 | 292.5 | 20.1% |
| 91st to 95th percentile | 31 | 210.3 | 14.5% |
| 96th to 99th percentile | 24 | 349.9 | 24.1% |
| >99th percentile | 6 | 381.1 | 26.2% |
Similar relationships between dose percentile rank and relative contribution to the cumulative radiation dose among structural interventionalists, interventional echocardiographers, scrub technologists, and nurse circulators were observed as in cases with coronary angiography (Table 2). Cases above the 90th percentile accounted for 51.3% of the cumulative radiation dose among structural interventionalists, 39.9% of the cumulative radiation dose among interventional echocardiographers, 45.8% of the cumulative radiation dose among scrub technologists, and 64.8% of the cumulative radiation dose among nurse circulators (Central Illustration).
Characteristics of cases above and below the 90th percentile radiation dose
Univariate comparisons of variables above and below the 90th percentile of physician radiation dose are shown in Table 3. Patient characteristics in cases with physician radiation dose above and below the 90th percentile were similar except for male sex and STEMI presentation, which were both significantly more frequent among cases above the 90th percentile (male sex: 80.6% vs 57.5%, P = .007; STEMI: 13.9% vs 1.5%, P = .001). Procedural characteristics were also similar in the 2 groups except for cases with PCI, which were more frequent among cases above the 90th percentile (63.9% vs 30.9%; P < .0001).
Table 3.
Univariate comparison of patient and procedural characteristics for cases above and below the 90th percentile physician radiation dose.
| ≤90th percentile (n = 327) | >90th percentile (n = 36) | P value | |
|---|---|---|---|
| Age, y | 68.1 ± 11.5 | 67.7 ± 12.8 | .84 |
| Body mass index, kg/m2 | 30.9 ± 6.8 | 32.6 ± 8.8 | .27 |
| Male sex | 188 (57.5) | 29 (80.6) | .007 |
| Arterial access | |||
| Femoral | 131 (40.1) | 16 (44.4) | .61 |
| Radial/brachial | 196 (59.9) | 20 (55.6) | |
| Fractional flow reserve | 47 (14.4) | 5 (13.9) | .94 |
| PCI | 101 (30.9) | 23 (63.9) | <.0001 |
| Right heart catheterization | 73 (22.3) | 12 (33.3) | .14 |
| Radiation-absorbing pad | 124 (38.5) | 14 (38.9) | .96 |
| STEMI | 5 (1.5) | 5 (13.9) | .001 |
| Fluoroscopy time, min | 5.4 (3.1-9.4) | 16.0 (12.9-23.0) | <.0001 |
| Air kerma, mGy | 735 (512-1052) | 1479 (1060-2008) | <.0001 |
| DAP, Gy·cm2 | 60.7 (41.7-86.8) | 109.8 (82.6-176.4) | <.0001 |
Age and body mass index are shown as mean ± SD. Radiation metrics are shown as median (IQR). All other values are n (%).
DAP, dose area product; PCI, percutaneous coronary intervention; STEMI, ST-segment elevation myocardial infarction.
In addition to dosimeter-derived physician radiation exposure, similar analyses were conducted exploring the association with patient-level radiation doses. All patient radiation dose metrics were significantly higher for cases above the 90th percentile physician radiation dose (Table 3), including a 3.0-fold higher fluoroscopy time (16.0 [12.9-23.0] minutes vs 5.4 [3.1-9.4] minutes, P < .0001), a 2.0-fold higher AK (1479 [1060-2008] mGy vs 735 [512-1052] mGy, P < .0001), and a 1.8-fold higher DAP (109.8 [82.6-176.4] Gy·cm2 vs 60.7 [41.7-86.8] Gy·cm2, P < .0001).
The results of a multivariable logistic regression model are shown in Table 4. STEMI (OR, 6.2 [1.5-26.3]; P = .01), performance of PCI (OR, 5.6 [2.2-14.2]; P < .001), RHC (OR; 4.4 [1.7-11.7]; P = .003), and male sex (OR, 3.2 [1.3-8.0]; P = .01) were all found to be independently associated with greater odds of a case having a physician radiation dose above the 90th percentile.
Table 4.
Variables identified in multivariate analysis to be independently associated with physician radiation dose above the 90th percentile.
| Odds ratio (95% CI) | P value | |
|---|---|---|
| STEMI | 6.2 (1.5-26.3) | .01 |
| Percutaneous coronary intervention | 5.6 (2.2-14.2) | <.001 |
| Right heart catheterization | 4.4 (1.7-11.7) | .003 |
| Male sex | 3.2 (1.3-8.0) | .01 |
STEMI, ST-segment elevation myocardial infarction.
Discussion
The principal finding of the present study is that high radiation dose outliers, which accounted for only a small fraction of the total cases performed, made a disproportionately large contribution to cumulative radiation doses among physicians in the catheterization laboratory. Accordingly, the highest 10% of physician radiation exposure cases accounted for 60% of the cumulative radiation dose among physicians performing coronary angiography. The disproportionately large contribution of high-dose outliers (cases above the 90th percentile) to the cumulative radiation dose was not limited to physicians performing coronary angiography; similar relationships were seen among structural interventionalists, interventional echocardiographers, scrub technologists, and nurse circulators. Additionally, we demonstrated that the most commonly reported measure comparing strategies to mitigate radiation exposure (median physician radiation dose per case) was found to be a poor marker of cumulative radiation exposure, as 50% of cases at or below the median accounted for a mere 5% of the cumulative physician radiation dose. Taken collectively, these observations suggest that high radiation dose outliers may be a target for future radiation mitigation efforts among practicing physicians and staff members in the catheterization laboratory.
Relevance of high radiation dose outliers
Regulatory bodies have set the annual dose limit for physicians and staff working in a catheterization laboratory at 50,000 μSv (50 mSv) in the US and 20,000 μSv (20 mSv) in Europe. The implications of reaching these dose limits are substantial, as physicians or staff members exceeding these cumulative dose thresholds are often forced to stop performing fluoroscopy-based procedures on a temporary basis, which can strain the local physician or staff workforce, negatively impact patient care, and have financial repercussions on physician or staff income. The fear of such consequences has led some physicians to omit wearing a required radiation dosimeter with the intent to avoid having their cumulative radiation dose documented, a practice recently reported in 17% of interventional cardiologists.11 It is important for physicians and staff to recognize that these dose limits represent cumulative doses acquired over the course of a year. Based on the findings of the present study, only 10% of the total cases they performed annually may contribute to half of their cumulative annual dose. It may, therefore, be helpful to provide additional focus on radiation safety practices targeting outlier cases.
Median dose and cumulative dose disconnect
In the present study, a seeming disconnect was observed between the median physician radiation dose per case and the cumulative radiation dose, such that 50% of cases below the median dose accounted for only 5% of the cumulative dose. The median dose per case has served as an important metric in both observational4,5 and randomized controlled studies6,12 evaluating radiation dose mitigation strategies using novel enhanced radiation protection devices (ERPD). It would be expected that any strategy effectively reducing the median radiation dose would also reduce cumulative dose. However, based on the results of the present study, any strategy that lowers median radiation dose without also addressing radiation dose outliers could conceivably have a blunted, even minor impact on cumulative radiation dose. Considering the contribution of radiation dose outliers to the cumulative dose, it may be even more meaningful in future studies of ERPD to evaluate their effect on radiation dose outlier cases above the 90th percentile.
Patient and procedural characteristics associated with outlier radiation doses
The risk of radiation health hazards has been shown in most models to increase linearly with cumulative radiation exposure.13 Given that more than half of the cumulative exposure arose from cases above the 90th percentile radiation dose, the findings of this study support radiation dose outliers as an important target for future radiation mitigation efforts. Recent endeavors to reduce occupational radiation exposure in the catheterization laboratory have led to the development of ERPD, which have been shown to dramatically reduce median radiation doses compared to conventional protection methods.4, 5, 6,12 ERPD have the potential to transform radiation safety in the catheterization laboratory and have demonstrated considerable growth and implementation in the past decade. Although effective at reducing median dose, cases below the median were observed to contribute to only 5% of the cumulative radiation dose in the present study. The impact of ERPD on outlier radiation doses remains unknown.
It is important to note that some studies of ERPD have either excluded cases with higher complexity14 or excluded cases that were emergent.6 It is possible that either emergent cases or those characterized by higher complexity might also be the ones most likely to result in physician and staff outlier radiation doses. The concept that emergent cases may result in higher physician radiation doses is supported by the present observation that STEMI cases had 6-fold greater odds of having a physician radiation exposure above the 90th percentile. Based on the results of the present study, applying ERPD to cases most prone to have outlier doses could yield the greatest reductions in cumulative radiation dose and, therefore, the greatest impact on radiation safety. In contrast, using ERPD during only low complexity and nonemergent cases might minimally affect physicians’ annual radiation doses, given the negligible effect on cumulative radiation doses. Identifying patient and procedural characteristics associated with outlier radiation doses is therefore important and clinically relevant because physicians are held to annual occupational limits. Whether intentionally funneling cases anticipated to be complex to procedure rooms having an ERPD available would result in lower radiation doses to physicians and staff members requires further study.
Considering cases above the 90th percentile for physician radiation dose accounted for more than half the cumulative dose, the 90th percentile may serve as a good target for identifying cases associated with high radiation dose outliers. In the present study, cases performed in patients with STEMI had the highest odds of having physician radiation doses above the 90th percentile. It is possible this finding could be attributable to radiation safety measures not being prioritized in emergent cases. Use of ERPD in STEMI cases, which could potentially mitigate outlier radiation doses, has not been adequately investigated. Whether the additional time required to set up an ERPD would adversely impact door-to-balloon times remains unknown, but based on the present observations should be explored. Coronary angiography cases that also involved PCI were observed to have 5-fold greater odds of having physician radiation doses above the 90th percentile. This finding is likely attributable to PCI routinely requiring more time and radiation to complete than diagnostic coronary angiography alone. Similarly, coronary cases in which RHC was performed carried a greater than 4-fold increase in the odds of having physician radiation doses above the 90th percentile. It is notable that physician radiation doses during RHC and endomyocardial biopsy were recently reported to be similar to those obtained during coronary angiography.15 This may in part be attributable to challenges encountered with obtaining good radiation shielding when performing RHC from the jugular approach. It is also possible that RHC may be a marker of a more complex coronary case. Whereas coronary angiography and RHC cases performed as part of a workup for valvular interventions are often simple, cases with RHC for management of patients with cardiogenic shock and cardiac arrest are more complex, often requiring substantially more time to complete. The association of male sex of the patient with physician radiation doses may be attributable to several factors, including the greater size of men compared to women, greater tissue density, or differing distribution of body mass. Although these factors intuitively make sense, patient body mass index was not observed to be associated with physician radiation doses above the 90th percentile, a somewhat surprising finding considering the previously demonstrated association between patient body mass index and physician radiation dose.8 Although the present study identified PCI, RHC, and male sex as independent predictors of cases having a physician radiation dose above the 90th percentile, additional studies are clearly needed at other centers to more completely identify patient and procedural characteristics likely to result in high outlier radiation doses.
Limitations
This investigation is limited by its single-center, observational study design. A multicenter study with a larger sample size is needed to confirm the present findings and assist with generalizability. Whether the present results can be extrapolated to cases performed at centers with different patient populations, procedural complexity, or after-hours case mix remains unknown. It is important to note that a large number of cases in the registry were excluded from this analysis due to the use of an ERPD or robotic system. It is therefore possible that the exclusion of cases that used these enhanced systems may have led to a biased sample in the study. Although this study collected data from 2 separate procedure rooms having identical fluoroscopy systems, we cannot exclude the possibility that there is unmeasured confounding arising from collecting data from 2 different rooms. This study is also limited, considering the measured cumulative dose was the cumulative dose taken across multiple individuals. Although this is an important limitation, cases in this study were consecutive cases performed within 2 procedural rooms. Whether a single physician performing these consecutive cases would have yielded differing results remains unknown. Data pertaining to individual physicians and their approaches to radiation safety were not recorded and thereby represents an additional limitation. The fact that cases performed outside of normal business hours were not included represents an important limitation. Cases performed outside of normal business hours are frequently emergent in nature; such cases, in turn, potentially increase the degree of complexity and therefore procedural duration and radiation exposure. Additional studies are needed to further investigate whether emergent cases result in higher physician radiation doses than nonemergent cases. Finally, these data were collected on coronary cases performed between 2015 and 2016. Radiation safety practices have evolved over the past decade. Confirmation of the present results in a more contemporary cohort is needed.
Conclusion
Physician radiation dose outliers contribute disproportionately to the cumulative radiation dose, with the top 10% of cases accounting for 60% of the cumulative dose. Based on these observations, high radiation dose outliers require additional study and may be a target for future radiation mitigation efforts.
Declaration of competing interest
Ryan D. Madder has received speaker honoraria from Abbott Vascular, Boston Scientific, and Corindus; has served as a consultant to Abbott Vascular, AngioWave Imaging, Boston Scientific, Nanoflex Robotics, Orchestra Biomed, RapidAI, and SpectraWAVE; has received research support from AngioWave Imaging, Corindus, Microbot Medical, and Nanoflex Robotics; and serves on the advisory boards of Boston Scientific, Gentuity, Medtronic, and SpectraWAVE. Devraj Sukul has served as a consultant to AngioWave Imaging and RapidAI. David A. McNamara receives funding from the American Society of Echocardiography for radiation-related research, separate from the current study. The other authors reported no financial interests.
Acknowledgments
Funding sources
This study was funded by Corewell Health and Corindus, a Siemens Healthineers Company.
Ethics statement and patient consent
This research adhered to relevant ethical guidelines. The local institutional review board approved the protocol and provided a waiver of consent for patients. All physicians and staff members participating in the study provided informed consent.
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