Each parameter (apron type and size, surgeon position, and C-arm projection) was tested 3 times, and the median radiation dose-equivalent rate (mrem/hr) for each dosimeter was calculated. A Wilcoxon rank-sum test was used to compare the median radiation dose-equivalent rate between pairs of groups (LIQ and UOQ, left and right breast, anteroposterior and lateral projection, torso facing the table and axilla facing the table, and male and female vests) and a Kruskal-Wallis test was used to compare the difference in radiation exposure according to apron size. A univariate linear regression analysis was used to evaluate the difference in radiation exposure to the LIQ and UOQ of the breast based on apron type, with a significance criterion of p < 0.05.
The median dose-equivalent rate of scatter radiation to the UOQ of the breast (0.40 mrem/hr) was higher than that to the LIQ of the breast (0.06 mrem/hr) (p = 0.05) across all testing (Table I). When comparing lead shielding to no lead shielding across all testing (both C-arm positions, surgeon positions, and all lead apron sizes), protective lead equipment resulted in lower median dose-equivalent rates for both cross-back apron use (0.20 mrem/hr) and vest use (0.19 mrem/hr) compared with no lead shielding (16.0 mrem/hr) (p = 0.0001). The vests and cross-back aprons provided no statistically significant difference in shielding of the UOQ (p = 0.86); the cross-back aprons were more effective than the vests at shielding the LIQ (p < 0.05) across all testing.
When comparing the C-arm positions across all apron types and sizes and surgeon positions, higher dose-equivalent rates were observed for both the UOQ and the LIQ in a C-arm lateral projection (0.98 mrem/hr) compared with an anteroposterior projection (0.13 mrem/hr) (p < 0.001). The median dose-equivalent rate observed with the torso phantom facing the table (0.19 mrem/hr) was lower than that with the torso at 90° (0.40 mrem/hr) (p = 0.13). The highest dose-equivalent rate for the left-breast UOQ was observed with the C-arm in the lateral position and with the torso facing the table (45.7 mrem/hr for no lead protection, 17.9 mrem/hr for vests, and 10.9 mrem/hr for cross-back aprons) (p < 0.01) (Fig. 5). The highest dose-equivalent rate for the right-breast UOQ was observed with the C-arm in the lateral position and with the torso at 90° (32.7 mrem/hr for no lead protection, 27.7 mrem/hr for vests, and 29.4 mrem/hr for cross-back aprons) (p = 0.67) (Fig. 6).
The median dose-equivalent rate of radiation to the UOQ observed for a medium-sized vest or apron, across all surgeon and C-arm positions, was 0.14 mrem/hr. Higher rates were observed for lead protection that was too small (size small, 0.18 mrem/hr) or too large (size extra-large, 0.37 mrem/hr), but these differences were not statistically significant. Larger aprons were more protective than small aprons in the C-arm anteroposterior projection and less protective in the C-arm lateral projection, although this was not statistically significant. The radiation dose-equivalent rates for male and female vests were not statistically significantly different.
Our study demonstrated that the breast is susceptible to intraoperative ionizing radiation exposure. The UOQ of the breast was exposed to higher scatter radiation doses than the LIQ. In some simulated scenarios, median dose-equivalent rates with lead protection (29.4 mrem/hr in the C-arm lateral projection and the torso at 90° to the table) approached those observed without lead protection (32.7 mrem/hr).
We hypothesized that aprons that were too large would be associated with increased radiation to the breast. Although the median dose-equivalent rate observed for the extra-large apron was higher than that observed for the small, medium, and large aprons, this difference was not statistically significant. Larger aprons demonstrated better protection in the C-arm anteroposterior projection than in the lateral projection, suggesting that the wider dimension provided better protection of the torso anteriorly but the larger arm holes exposed the axilla laterally (Fig. 3). Interestingly, the small apron also had a higher median dose-equivalent rate than that of the medium-sized apron. One explanation is that the small apron was too narrow for the medium-sized torso, leaving the axilla exposed. A second explanation is that the 2 panels of the small vest (each of 0.25-mm lead equivalence) did not completely overlap on a medium-sized torso, resulting in <0.5 mm of lead protection (Fig. 4). This is further supported by our finding that the LIQ was exposed to higher doses of radiation when protected by vests compared with cross-back aprons. Vests with a 0.5-mm lead equivalence for each front panel may better protect the LIQ of the breast from radiation exposure. Although not tested in our study, pregnancy aprons (1.0-mm lead equivalence), custom aprons, and aprons with sleeves may provide better protection to both the UOQ and LIQ of the breast.
Similar to the findings of other studies, our results suggest that the C-arm lateral projection increases scatter radiation doses to the surgeon1,3,4. When possible, the surgeon should be positioned next to the image intensifier; however, there are scenarios in which the surgeon is positioned next to the x-ray tube, such as for lateral hip imaging during placement of a cephalomedullary nail and lateral imaging of the knee and ankle. This position places the UOQ of the breast closer to the x-ray source and at a higher risk of scatter radiation exposure. Distancing the axilla from the C-arm and placing the x-ray source beneath the operating table or on the contralateral side of the table is recommended to reduce radiation exposure to the UOQ of the breast.
There are limitations to applying our data from a simulated setting using anthropomorphic phantoms to a clinical setting with orthopaedic surgeons. However, as an illustrative example, if we take the highest rate recorded in our study for a scenario in which the phantom was shielded by lead protection (29.4 mrem/hr, with the C-arm in a cross-table lateral position and the torso at 90°) and assume an average of 5 minutes of fluoroscopy for a femoral intramedullary nailing case as previously reported16, this would allow a surgeon to perform 800 such cases per year before reaching the annual dose limit for torso exposure. Our data suggest that an orthopaedic surgeon could use 4,000 minutes of fluoroscopy per year before reaching annual dose limits. Although this is more fluoroscopy than most orthopaedic surgeons perform in 1 year, it is shorter than that previously reported for the lens of the eye (4,949 to 11,459 minutes) or the thyroid (6,406 to 19,194 minutes), and is based on the annual dose limit to the torso (not the breast), since annual occupational dose limits to the breast have not yet been established1. This example does not illustrate the stochastic effects of cancer, where long-term radiation exposure may increase malignancy risk without a threshold dose. In 2007, the ICRP estimated an increased risk of radiation-induced breast cancer death that was twice as high as its 1977 and 1991 estimates, suggesting that the risks of ionizing radiation to the breast may be higher than previously perceived17. The orthopaedic surgeon exposed to intraoperative fluoroscopy over a career has a cumulative risk of ionizing radiation exposure and may be at higher risk of radiation-induced breast cancer9,18. Until the cumulative risk of breast cancer due to low-dose radiation is better understood, we recommend lead protection to reduce intraoperative radiation exposure and distancing oneself from the x-ray source when obtaining lateral images.
With an increasing number of women in orthopaedic surgery resident training programs (6.9% in 1997, 13.1% in 2009, and 14% in 2013), studies that evaluate sex-specific occupational risks in orthopaedic surgery are warranted19,20. The cause of breast cancer is multifactorial. Chou et al. reported that, compared with the U.S. female population, female orthopaedic surgeons had both more protective factors (lower body mass index, less smoking, and lower postmenopausal hormone use) and more predisposing factors (increased age at first childbirth and nulliparity)6. A follow-up study comparing female orthopaedic surgeons with plastic surgeons and urologists with similar predisposing factors found no difference between the observed and expected prevalence of breast cancer among plastic surgeons and urologists. More urologists in that study (54%) reported using standard fluoroscopy >1 time per week compared with orthopaedic surgeons (37%); however, more orthopaedic surgeons (31%) reported using mini-fluoroscopy >1 time per week compared with urologists (4%), suggesting that mini-fluoroscope use may be associated with increased breast cancer prevalence21.
Our study used a standard fluoroscope. Recent studies have compared the radiation exposure of standard fluoroscopes with that of mini-fluoroscopes. The mini-fluoroscope produces less current than does the standard fluoroscope, but is often used with the x-ray source closer to the patient, which increases the scatter radiation compared with the standard fluoroscope (where the x-ray source is placed beneath the operating table and radiation is scattered toward the floor)22,23. Additional studies are warranted to evaluate radiation exposure to the breast using a mini-fluoroscope, which may place the breast closer to the x-ray source and increase radiation exposure.
Interventional radiologists, vascular surgeons, and gastroenterologists are also at risk of intraoperative radiation exposure24-26. A meta-analysis of fluoroscopically guided procedures showed a higher effective dose for orthopaedic procedures (2.5 to 88 μSv for extremity nailing and 0.1 to 101 μSv for vertebroplasty) compared with urology procedures (1.7 to 56 μSv for percutaneous nephrolithotomy), gastrointestinal procedures (2.0 to 46 μSv for biliary tract procedures), and vascular procedures (1.8 to 53 μSv for head/neck endovascular procedures). The median radiation dose per case to the unshielded operator was highest at the level of the trunk (302 μSv) compared with the eye (113 μSv) and neck (75 μSv)24. No studies, to our knowledge, have evaluated radiation exposure to the breast in these populations.
Our study had limitations. First, the study was performed in a simulated operating-room setting; our findings may not be directly applicable to the orthopaedic surgeon in a setting with different patient and surgeon characteristics and fluoroscopy positioning and settings. The phantom also did not have arms, which may help to shield the breast from radiation exposure. Although we used a female torso phantom in our study, male orthopaedic surgeons may also be at risk of radiation-induced breast cancer. Second, the dosimeters used in our study detected a minimum scatter radiation of 0.1 mrem/hr with an accuracy of ±30% below 50 keV. Prior to data collection, the dosimeters were validated with a first-order air exposure intercomparison test using the C-arm x-ray photon energy for comparison. Scatter radiation dose-equivalent rates of <0.1 mrem/hr were not detected with the dosimeters used in our study, and thus the results may underestimate the total radiation dose-equivalent rate to the breast. The dosimeters were selected for their compact size, which allowed for insertion within the torso phantom to measure radiation exposure to the LIQ of the breast. Although not significant, facing the dosimeters at 90° to the radiation source decreased radiation dose-equivalent rates. Thus, our results may underestimate the exposure of the LIQ of the breast to radiation in an in vivo setting. Finally, our study does not demonstrate causality between radiation exposure and breast cancer. Additional studies are warranted to elucidate the risks of ionizing radiation and to establish annual dose limits for occupational exposure to the breast.
The results of our study suggest that the breast is an area that may not be adequately protected by standard cross-back aprons and vests. Methods of reducing exposure are warranted. To limit intraoperative radiation exposure, we recommend the following: (1) using properly fitted lead aprons and/or vests to protect the breast, (2) increasing the distance between the surgeon and the x-ray source, especially with use of the C-arm in the lateral position, (3) increasing the distance between the x-ray source and the patient to decrease scatter radiation, (4) positioning the x-ray source beneath the operating table or on the contralateral side of the surgeon when possible, and (5) educating surgeons and trainees about radiation safety. Modifications to lead aprons, new apron designs including axillary wings, or custom lead aprons may provide better protection of the breast tissue in orthopaedic surgeons.
Investigation performed at the University of California, San Francisco Medical Center, San Francisco, California
Disclosure: This study was supported by research grants from the Orthopaedic Research and Education Foundation and the Institute of Clinical and Translational Sciences. On the Disclosure of Potential Conflicts of Interest forms, which are provided with the online version of the article, one or more of the authors checked “yes” to indicate that the author had a relevant financial relationship in the biomedical arena outside the submitted work.
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