Abstract
Background
The impact of patient obesity on scrub technologist radiation dose during coronary angiography has not been adequately studied.
Methods
Real-time radiation exposure data were prospectively collected during consecutive coronary angiography cases. Patient radiation dose was estimated by dose area product (DAP). Technologist radiation dose was recorded by a dosimeter as the personal dose equivalent (H p (10)). Patients were categorized according to their body mass index (BMI): <25.0, lean; 25.0–29.9, overweight; ≥30.0, obese. The study had two phases: in Phase I ( N = 351) standard radiation protection measures were used; and in Phase II ( N = 268) standard radiation protection measures were combined with an accessory lead shield placed between the technologist and patient.
Results
In 619 consecutive coronary angiography procedures, significant increases in patient and technologist radiation doses were observed across increasing patient BMI categories ( p < 0.001 for both). Compared to lean patients, patient obesity was associated with a 1.7-fold increase in DAP (73.0 [52.7, 127.5] mGy × cm 2 vs 43.6 [25.1, 65.7] mGy × cm 2 , p < 0.001) and a 1.8-fold increase in technologist radiation dose (1.1 [0.3, 2.7] μSv vs 0.6 [0.1, 1.6] μSv, p < 0.001). Compared to Phase I, use of an accessory lead shield in Phase II was associated with a 62.5% reduction in technologist radiation dose when used in obese patients ( p < 0.001).
Conclusions
During coronary angiography procedures, patient obesity was associated with a significant increase in scrub technologist radiation dose. This increase in technologist radiation dose in obese patients may be mitigated by use of an accessory lead shield.
Highlights
- •
Coronary angiography in obese patients was associated with a near doubling of technologist radiation dose.
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In obesity patients, use of an accessory lead shield was associated with reduced radiation doses among scrub technologists.
- •
More studies are needed to identify additional factors that reduce staff radiation doses when treating obese patients.
1
Introduction
Studies evaluating the occupational hazards of working in the cardiac catheterization laboratory have focused largely on the risks posed to interventional cardiologists [ ]. Several recent publications indicate that many of these risks may extend to procedural staff members. As such, concern has been raised that nurses and scrub technologists working in the catheterization laboratory may be at increased risk of premature cataract formation, stroke, and possibly cancer [ ]. Given a growing awareness for these potential risks to staff members, additional studies are needed to identify procedural factors that increase staff irradiation.
The primary source of occupational radiation exposure to physicians and staff members during cardiac catheterization is scatter radiation emitted from the patient. Larger radiation doses are needed to produce adequate images in obese patients, which results in greater scatter radiation being emitted from the patient in the setting of obesity [ ]. Considering the effect of obesity on scatter radiation, the obesity epidemic has the potential to alter the occupational risks of those working in the catheterization laboratory. Whether an accessory lead shield, which was previously shown to be associated with a reduction in technologist radiation dose during cardiac catheterization [ ], effectively reduces technologist radiation exposure in the setting of patient obesity is unknown. This study was performed to explore the impact of patient obesity on scrub technologist radiation dose during coronary angiography and to determine if use of an accessory lead shield was associated with reductions in technologist radiation exposure in obese patients.
2
Methods
2.1
Study population
The Combining Robotic-Stenting and Proactive Shielding Techniques in the Catheterization Laboratory to Achieve Lowest Possible Radiation Exposure to Physicians and Staff (SHIELD) study was a single-center prospective observational study, designed to investigate radiation exposure to physicians and staff members in the cardiac catheterization laboratory [ , ]. The study was conceived, designed, and conducted by investigators of the Frederik Meijer Heart & Vascular Institute of Spectrum Health (Grand Rapids, Michigan). The local institutional review board approved the protocol, and all participants provided informed consent.
Data on radiation exposure were prospectively collected on consecutive cases in a single fluoroscopy suite having an Allura Xper FD10 X-ray system (Philips, Amsterdam, The Netherlands). 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. A total of 26 physicians who perform cardiac catheterization at the study institution consented to participate. Cases that did not utilize any radiation were excluded as specified in the study protocol. For the purposes of this analysis, only those procedures in which coronary angiography was performed and in which scrub technologist radiation doses were measured were included. Procedures not involving coronary angiography, including stand-alone right heart catheterizations and pacemaker implantations, were excluded from this analysis.
2.2
Radiation monitoring
At the study institution, the scrub technologist stands to the right of the operating physician and serves as a second operator during the case, assists the operating physician in device exchanges, performs all injections using a contrast delivery system (Acist CVi, Acist Medical Systems, Eden Prairie, Minnesota), and inflates angioplasty and stent balloons. Real-time radiation exposure data were prospectively collected on technologists using a commercially available dosimetry system that contains a bedside monitor capable of displaying real-time radiation exposure data (RaySafe i2, Unfors RaySafe, Billdal, Sweden). During the study, the technologist wore a dosimeter located on either the left anterior side of the glasses or on the left anterior side of the thyroid collar. Physicians and all staff members, including technologists, were blinded to the monitor display and to the radiation data collected by the dosimeters for the duration of the study.
2.3
Radiation protection
Two ancillary lead shields were used in all cases per standard operating protocol at the study institution. These included 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 [ ]. In all cases, scrub technologists wore traditional lead apparel, consisting of a lead skirt, apron, and thyroid collar. In order to determine the impact of accessory lead shields on technologist radiation exposure, the study was divided into two phases as previously described [ ]. During Phase I, all cases were performed using the standard radiation protective measures described above. In Phase II, all cases were performed using standard radiation protective measures in combination with a dedicated accessory lead shield for each scrub technologist. The accessory lead shields used in this study (height 1.8 m/width 0.7 m) had an effective lead thickness of 0.5 mm Pb ( Fig. 1 ). For technologists, the shield was positioned near the foot of the bed enabling them to stand behind the shield while performing injections with a contrast delivery system.
2.4
Patient and technologist radiation doses
Radiation metrics recorded for each case included the fluoroscopy time, air kerma (AK), and dose area product (DAP), which were automatically calculated by the fluoroscopy imaging system. Consistent with prior methodology, the patient radiation dose per case was estimated by the DAP [ , , ]. The technologist radiation dose per case was the personal dose equivalent (H p (10)), as recorded and reported directly by the dosimetry system.
2.5
Statistical analysis
For analytical purposes, patients were categorized into the following subgroups based on BMI: <25.0, lean; 25.0–29.9, overweight; ≥30.0, obese. Descriptive statistics were used to summarize baseline characteristics and outcome measures. Normally distributed continuous variables are shown as mean ± standard deviation. Non-normally distributed continuous variables are shown as median [25th percentile, 75th percentile]. Categorical variables are shown as count (% frequency). p -Values for comparison of continuous variables were derived from two sample independent t -tests if data were normally distributed or from Wilcoxon rank sum tests if data were not normally distributed. p -Values for comparison of categorical variables were generated with a Chi-square analysis or a Fisher’s exact test if the expected cell counts were below 5 in >20% of the cells. p -Values for the comparison of the three BMI categories were derived from a Kruskal-Wallis analysis. To determine where the differences occurred between the three groups, Bonferroni correction was used on Wilcoxon Rank Sum p -values. All statistical analyses were generated using SAS (SAS Enterprise Guide software, Version 7.1, SAS Institute Inc., Cary, NC).
2
Methods
2.1
Study population
The Combining Robotic-Stenting and Proactive Shielding Techniques in the Catheterization Laboratory to Achieve Lowest Possible Radiation Exposure to Physicians and Staff (SHIELD) study was a single-center prospective observational study, designed to investigate radiation exposure to physicians and staff members in the cardiac catheterization laboratory [ , ]. The study was conceived, designed, and conducted by investigators of the Frederik Meijer Heart & Vascular Institute of Spectrum Health (Grand Rapids, Michigan). The local institutional review board approved the protocol, and all participants provided informed consent.
Data on radiation exposure were prospectively collected on consecutive cases in a single fluoroscopy suite having an Allura Xper FD10 X-ray system (Philips, Amsterdam, The Netherlands). 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. A total of 26 physicians who perform cardiac catheterization at the study institution consented to participate. Cases that did not utilize any radiation were excluded as specified in the study protocol. For the purposes of this analysis, only those procedures in which coronary angiography was performed and in which scrub technologist radiation doses were measured were included. Procedures not involving coronary angiography, including stand-alone right heart catheterizations and pacemaker implantations, were excluded from this analysis.
2.2
Radiation monitoring
At the study institution, the scrub technologist stands to the right of the operating physician and serves as a second operator during the case, assists the operating physician in device exchanges, performs all injections using a contrast delivery system (Acist CVi, Acist Medical Systems, Eden Prairie, Minnesota), and inflates angioplasty and stent balloons. Real-time radiation exposure data were prospectively collected on technologists using a commercially available dosimetry system that contains a bedside monitor capable of displaying real-time radiation exposure data (RaySafe i2, Unfors RaySafe, Billdal, Sweden). During the study, the technologist wore a dosimeter located on either the left anterior side of the glasses or on the left anterior side of the thyroid collar. Physicians and all staff members, including technologists, were blinded to the monitor display and to the radiation data collected by the dosimeters for the duration of the study.
2.3
Radiation protection
Two ancillary lead shields were used in all cases per standard operating protocol at the study institution. These included 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 [ ]. In all cases, scrub technologists wore traditional lead apparel, consisting of a lead skirt, apron, and thyroid collar. In order to determine the impact of accessory lead shields on technologist radiation exposure, the study was divided into two phases as previously described [ ]. During Phase I, all cases were performed using the standard radiation protective measures described above. In Phase II, all cases were performed using standard radiation protective measures in combination with a dedicated accessory lead shield for each scrub technologist. The accessory lead shields used in this study (height 1.8 m/width 0.7 m) had an effective lead thickness of 0.5 mm Pb ( Fig. 1 ). For technologists, the shield was positioned near the foot of the bed enabling them to stand behind the shield while performing injections with a contrast delivery system.
2.4
Patient and technologist radiation doses
Radiation metrics recorded for each case included the fluoroscopy time, air kerma (AK), and dose area product (DAP), which were automatically calculated by the fluoroscopy imaging system. Consistent with prior methodology, the patient radiation dose per case was estimated by the DAP [ , , ]. The technologist radiation dose per case was the personal dose equivalent (H p (10)), as recorded and reported directly by the dosimetry system.
2.5
Statistical analysis
For analytical purposes, patients were categorized into the following subgroups based on BMI: <25.0, lean; 25.0–29.9, overweight; ≥30.0, obese. Descriptive statistics were used to summarize baseline characteristics and outcome measures. Normally distributed continuous variables are shown as mean ± standard deviation. Non-normally distributed continuous variables are shown as median [25th percentile, 75th percentile]. Categorical variables are shown as count (% frequency). p -Values for comparison of continuous variables were derived from two sample independent t -tests if data were normally distributed or from Wilcoxon rank sum tests if data were not normally distributed. p -Values for comparison of categorical variables were generated with a Chi-square analysis or a Fisher’s exact test if the expected cell counts were below 5 in >20% of the cells. p -Values for the comparison of the three BMI categories were derived from a Kruskal-Wallis analysis. To determine where the differences occurred between the three groups, Bonferroni correction was used on Wilcoxon Rank Sum p -values. All statistical analyses were generated using SAS (SAS Enterprise Guide software, Version 7.1, SAS Institute Inc., Cary, NC).
3
Results
3.1
Study population
Between August 3, 2015 and February 26, 2016, scrub technologist radiation doses were recorded in 619 cases in which coronary angiography was performed. Patient and procedural characteristics are summarized in Table 1 . The distribution of patients according to BMI is presented in Fig. 2 . Overall, 18.3% of patients were categorized as lean and 81.7% of patients were either overweight or obese. Obesity was present in 48.3% of patients. Across the three BMI categories, procedural characteristics were not significantly different for the frequency of percutaneous coronary intervention (PCI) ( p = 0.15), fractional flow reserve ( p = 0.86), or right heart catheterization ( p = 0.69). Likewise, there were no significant differences in fluoroscopy times per case across BMI categories ( p = 0.48, Table 2 ).
| Total N = 619 | Phase I N = 351 | Phase II N = 268 | p -Value | |
|---|---|---|---|---|
| Age (years) | 65.7 ± 12.0 | 65.9 ± 11.6 | 65.4 ± 12.6 | 0.61 |
| Height (cm) | 173.2 ± 10.0 | 173.4 ± 10.0 | 172.9 ± 10.1 | 0.58 |
| Weight (kg) | 91.6 ± 21.6 | 92.4 ± 21.7 | 90.6 ± 21.3 | 0.30 |
| BMI | 30.5 ± 6.6 | 30.7 ± 6.7 | 30.2 ± 6.5 | 0.38 |
| Arterial access | ||||
| Femoral access | 221 (35.8) | 124 (35.5) | 97 (36.2) | 0.66 |
| Radial access | 394 (63.9) | 223 (63.9) | 171 (63.8) | |
| Brachial access | 2 (0.3) | 2 (0.6) | 0 (0.0) | |
| FFR | 64 (10.3) | 36 (10.3) | 28 (10.4) | 0.94 |
| PCI | 170 (28.7) | 100 (29.7) | 70 (27.5) | 0.55 |
| RHC | 148 (23.9) | 83 (23.6) | 65 (24.3) | 0.86 |
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