Effects of Real-Time Dosimetry on Staff Radiation Exposure in the Cardiac Catheterization Laboratory

Objectives. Radiation protection is essential for staff of cardiac catheterization laboratories in order to prevent long-term radiation-associated injury and disease. Instant feedback about the actual received dose may help operators to optimize the use of existing shielding devices. Therefore, the current study was designed to investigate whether routine use of real-time dosimetry may be able to reduce staff radiation exposure. Methods and Results. Over a period of 72 days, operators and assisting nurses were equipped with RaySafe i3 real-time dosimeters (Unfors RaySafe AB), but had no access to the dosimetry results during the first half of the study. This was followed by a second period that allowed operators to modify their behavior according to the dosimetry results. Compared with the first phase, the knowledge of real-time dosimetry results led to a uniform reduction in radiation exposure of all team members by approximately 60%, independent of the chosen vascular access. There were no significant changes in fluoroscopy time, dose-area product, or patient characteristics. Conclusions. Real-time dosimetry effectively reduced staff radiation exposure in the cardiac catheterization laboratory. This change was caused by optimized use of existing shielding equipment since no modifications of the general procedural approach or patient characteristics had occurred.

Reprinted with permission from J INVASIVE CARDIOL 2021;33(5):E337-E341. Epub 2021 April 5.

Key words: cardiac interventions, dosimetry, radiation protection

Cardiac interventions are increasingly performed worldwide, driven in particular by the emerging field of valvular and structural heart interventions. However, coronary interventions remain the mainstay of all diagnostic and therapeutic interventions due to the high prevalence of atherosclerotic coronary artery disease. Nearly all cardiac interventions require x-ray based imaging, while increased procedure numbers and complexity create a potential hazard for the involved staff by accumulating exposure to scattered radiation. As a consequence, interventional cardiologists receive the highest amounts of radiation among medical personnel¹ and bear an increased risk for cataract^2,3 or even malignancies including brain or neck tumors.⁴

Besides advancements in the technology of fluoroscopy workplaces, the use of shielding devices and adequate behavior in the catheterization laboratory are most effective in reducing staff radiation exposure. Today, real-time dosimetry can provide information about the effective use of these measures and may uncover specific shielding needs in individual treatment scenarios with respect to access site (eg, femoral or radial) or the use of additional equipment (eg, optical coherence tomography, fractional flow reserve, rotablation, and circulatory support).

Since real-time dosimetry enables staff to adapt their behavior in order to minimize unnecessary radiation, we investigated whether adding this technique to our daily practice would result in lower radiation exposure. For this purpose, we recorded individual staff dosimetry data before and after access to the real-time dosimetry results. During the first period, interventionalists and assisting personnel wore individual real-time dosimeters, but the results were not displayed inside the catheterization laboratory. During the second period, the operating cardiologist as well as assisting staff had access to the results of online dosimetry during the procedure and were able to adapt their behavior and the use of shielding accordingly. The goal of our study was to quantify a possible reduction of radiation exposure by the use of real-time dosimetry with respect to individual operators and access site.

Cardiac catheterization laboratory set-up and description of included coronary procedures. From June 3, 2019 to August 14, 2019, a total of 270 coronary procedures were performed in one of the two cardiac catheterization laboratories at the General Hospital Celle, Germany. The laboratory is equipped with a monoplane Allura Xper FD 10 angiography unit (Philips) built in 2013. Procedures included diagnostic angiographies as well as percutaneous coronary interventions. The access site was left to the operator’s discretion and included transfemoral or transradial approaches. All procedures were exclusively performed by experienced cardiologists with at least 500 cases as first operator. No educational angiographies or interventions were included. Importantly, no changes in procedural strategies were allowed in order to prevent changes in dosimetry results not related to optimized shielding and/or staff behavior.

For all patient data, ethical approval was waived by the local ethics committee of the Ärztekammer Niedersachsen (Bo/19/2020) in view of the retrospective nature of the study and all the procedures being performed were part of the routine care. Regarding staff dosimetry data, all team members gave their informed consent to participate in the study.

Radiation protection equipment. All staff members working inside the cardiac catheterization laboratory wore protective lead aprons including thyroid collars. Operators had individual leaded glasses. Shielding devices included table-mounted lead curtains with an upper shield, ceiling suspended lead-acrylic shields with x-ray protective strips (OT54001), as well as a separate, sterile covered and reusable shielding drape (ST-FS5AMM, all from MAVIG GmbH). For radial procedures, a large shielding drape (60 x 80 cm) was placed on the lower abdomen; for femoral procedures, the same shielding drape was placed on the legs just caudal to the access site (Figure 1).

Real-time dosimetry. For the duration of the investigation, the manufacturer (Unfors RaySafe AB) provided a RaySafe i3 system including 3 individual dosimeters and a separate screen to visualize real-time dosimetry results inside the catheterization laboratory. Each detector was worn at the outer side of the x-ray protective clothing (left side of the thyroid collar). Radiation exposure was analyzed every second during the time of each procedure and obtained cumulative dose (µSv) was transmitted wireless to the display. In the first part of the study, operators and assisting staff wore individual dosimeters without access to the results inside the catheterization laboratory (“blinded period”), while in the second period the system was used with instant visualization of the radiation exposure results for all staff members (“unblinded period”).

Statistical analysis. Continuous variables are presented as mean ± standard error of the mean, significance was tested by an unpaired t-test or Mann-Whitney test as applicable. D’Agostino-Pearson test was used to assess normal distribution. Discrete variables are displayed as counts and percentages and were compared with the Chi-squared test. P-values of <.05 were considered statistically significant.

Patient and procedural data. We analyzed data from 270 consecutive coronary catheterization procedures between June 3, 2019 and August 14, 2019 at our institution (General Hospital Celle, Germany). Of all included patients, 121 (44.8%) underwent coronary interventions. Transradial access was performed in 106 cases (39.3%), while transfemoral access was performed in 163 patients (60.4%). The majority of procedures included a diagnostic angiogram, while coronary interventions were performed in 43.4% of all cases during the blinded period and in 46% during the unblinded period (Table 1). Biometric data of patients, including weight, height, or body mass index, were comparable between the two periods. Even more important, no significant difference was observed regarding fluoroscopy time (7.0 ± 0.6 minutes during the blinded period vs 8.2 ± 0.6 minutes during the unblinded period) or dose area product (15.2 ± 1.3 Gy•cm² during the blinded period vs 15.4 ± 1.2 Gy•cm² during the unblinded period), indicating that no change in radiation protocols or strategies occurred between both observation periods (Table 1).

Effects of real-time dosimetry on overall staff radiation exposure. Real-time dosimetry led to ~60% reduction in operator and assisting nurse radiation exposure during the unblinded period, as illustrated in Figure 2A (operator, 0.55 ± 0.08 µSv vs 1.40 ± 0.21 µSv during the blinded period [P<.01]; assisting nurse, 0.07 ± 0.02 µSv vs 0.19 ± 0.03 µSv during the blinded period [P<.01]). A similar trend was observed for circulating nurses (0.02 ± 0.01 µSv vs 0.06 ± 0.02 µSv during the blinded period; P=.23).

Radiation exposure with respect to access route. Different access routes change the set-up and shielding options in the catheterization laboratory and might therefore affect staff radiation exposure. We analyzed our data separately for transradial vs transfemoral procedures and found a similar magnitude of staff dose reduction by the use of real-time dosimetry. Again, these results were significant for operators and assisting nurses while the same trend was observed for circulating nurses (Figures 2B and 2C). Importantly, no change was observed in patient radiation exposure as indicated by the comparable dose-area product (transradial access, 15.7 ± 1.06 Gy•cm² during the blinded period vs 15.1 ± 1.00 Gy•cm² during the unblinded period [P=.99]; transfemoral access, 14.9 ± 1.98 Gy•cm² during the blinded period vs 15.6 ± 1.36 Gy•cm² during the unblinded period [P=.29]).

Individual radiation exposure of different operators. Protective behavior and the use of protection devices varies among individual operators and could therefore attenuate the beneficial effects of real-time dosimetry. We separately analyzed radiation exposure data from 4 operators who performed the highest number of cases during the observation period. For all operators, a similar degree of dose reduction by real-time dosimetry was observed despite a variation in baseline levels (Table 2; Figure 2D).

Interventional cardiology is one of the most dynamic fields in medicine and has made dramatic progress over the last 2 decades. With increasing procedure numbers, radiation exposure to the catheterization laboratory personnel accumulates¹ and may result in serious adverse health effects including cataract formation³ or malignancies.⁴ Therefore, all preventive measures leading to a sustained reduction of radiation exposure should be utilized. Technological advances have led to excellent visibility despite low x-ray dose levels, and applications such as “last image hold” or fusion imaging have further diminished necessary fluoroscopy times and intensity. However, the major part of radiation protection is based on continuous educational efforts in order to avoid any unnecessary radiation. This will reduce both the effective dose applied to the patient as well as staff exposure by less scattered radiation.⁵ Regarding the latter, keeping maximal possible distance to the table as well as the use of personal and installed shielding devices⁶ are important factors. Real-time dosimetry has been introduced as a tool to visualize radiation exposure immediately, thereby allowing users to adapt their behavior and the use of shielding accordingly.⁷

In the current study, we analyzed the effects of implementing a real-time dosimetry system (RaySafe i3) on staff radiation exposure during routine procedures in the cardiac catheterization laboratory. We found that the use of real-time dosimetry led to a 60% reduction of staff radiation exposure, which is similar to the results reported in an interventional radiology setting.^7,8 This change was significant in personnel with the highest exposure dose (operators, assisting nurses), while the same trend was seen in the less-exposed circulating nurses. Importantly, the applied patient dose in terms of dose-area product or fluoroscopy time was not significantly different between both observation periods. Since no changes in procedural strategies (eg, the use of angulations with less exposure, abandoned cine sequences) were allowed, the observed staff dose reduction must be attributed to the optimized use of existing shielding devices and adequate behavior in the catheterization laboratory.

We found that the degree of dose reduction by real-time dosimetry was independent of the chosen access site. This is important and shows a particular strength of instantaneous dose feedback as it allows a quick adaptation to different set-ups and individual procedural settings. Moreover, individual operators achieved a similar reduction of radiation exposure, although baseline levels were quite different (up to 6 times compared with the lowest operator dose). This result indicates that a further dose reduction is still possible even for operators who already incorporated radiation protection as a fundamental part of their daily practice.

Study limitations. Despite these clear and encouraging results, our study has several limitations. First, the number of included patients is limited and may have prevented statistical significance for some of the observed trends. Moreover, the amount of dose reduction by real-time dosimetry depends on individual availability of shielding devices and motivation of all team members and may be less prominent in other settings. Our study did not assess effects of individual strategies or procedural preferences, although real-time dosimetry may also be used to modify the general procedural approach in future investigations. All procedural details and settings such as access route or standard angulations were left to the operator’s discretion in order to allow a broad translation of our results for varying settings. However, all operators were instructed to maintain their general procedural approaches during the course of the study. Although we demonstrate a significant effect of real-time dosimetry on individual radiation exposure, we cannot predict whether this effect may be maintained over time (even without further use of real-time dosimetry) as staff members may have been “educated” by the system regarding their deficiencies in radiation protection.⁸

Our study is the first to identify real-time dosimetry as an effective concept to reduce staff radiation exposure in the cardiac catheterization laboratory. Hospitals that offer invasive cardiology should consider the implementation of this technique to protect their employees from radiation-associated health hazards. 

Acknowledgments. We thank the nursing staff of the cardiac catheterization laboratory at the General Hospital Celle for excellent technical assistance and MD Solutions/Unfors RaySafe for providing the i3 real-time dosimetry device for this study. Data of the present study are part of the medical thesis of co-author Dilschad Murat, MD.

From the ¹Department of Cardiology, Allgemeines Krankenhaus Celle, Celle, Germany; and the ²Department of Cardiology 1, Center for Cardiology, Universitätsmedizin Mainz, Mainz, Germany.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.

Manuscript accepted November 5, 2020.

Address for correspondence: Eberhard Schulz, MD, Department of Cardiology, Allgemeines Krankenhaus Celle, 29223 Celle, Germany. Email: eberhard.schulz@akh-celle.de.