Use of a Disposable Radiation Protective Table

for Reducing Operator Radiation Exposure during Cardiovascular Angiographic Procedures

Introduction

The use of fluoroscopic imaging continues to increase during medical procedures. Fluoroscopic imaging plays a fundamental role in the diagnostic and treatment of cardiac and vascular disease. The cumulative operator and/or staff occupational exposure from scatter radiation may be considerable.¹ Cardiologists are the most common physician specialty with overexposure to radiation, and the number is felt to be grossly underreported.² The risk of these exposures may not be appreciated by physicians because the adverse consequence is not immediate. Though occupational radiation exposure for health care personnel has long been felt to have a minimum threshold that is safe and acceptable, this hypothesis has been shown to be in error. Research shows that there is no threshold of exposure below which low levels can be demonstrated to be harmless or beneficial. The health risk, particularly the development of solid cancers rises proportionally with exposure. The Occupational Safety and Health Administration (OSHA) is re-evaluating the current guidelines for occupational exposure.³ It appears reasonable to assume with the recent release of the Biological Effects of Ionizing Radiation (BEIR VII) report that the guidelines for the principle of ALARA (as low as reasonably achievable) will be substantially strengthened.⁴ This study evaluates a new radiation protection device intended to reduce radiation exposure to health care workers during cardiovascular angiographic procedures.

Materials and Methods

Description of radiation shielding device. The radiation shielding device consisted of a fiber board table with a side layer of radiation absorbing material consisting of a polymer impregnated with barium equivalent to .25 inches of lead with dimensions of 80 cm by 12 cm. (The Protector, Vascular Performance Products, Caledonia, Michigan). The table is placed from knee to ankle and rests under the sterile drape acting as a equipment platform as well.

Physician and patient characteristics. This study was conducted from 3/25/05 to 4/12/05 in the cardiac catheterization laboratories at a large tertiary hospital. On average, over 14,000 angiographic procedures, which include over 1500 peripheral vascular procedures, are completed in this department each year. The catheterization staff undergoes annual continuing education on radiation exposure. All participating physicians are board certified in cardiology and annually perform more than 500 procedures. The patient population included 50 patients referred for diagnostic left heart catheterization and underwent written informed consent. The patients mean age was 70.0 (± 12.1) years with 33 male and 17 female. Average body surface area was 2.0 cm2, with an average weight 94.3 ± 29.5 Kg and height 171.2 cm. Fluoroscopic System and Radiation Measurement: Catheterizations and angiography were performed on single-plane angiographic systems (Integris V5000 and H 5000, Phillips, Eindhoven, Netherlands). The image intensifier was routinely set on 7 inch mode for coronary angiography and 9 inch for ventriculography considered standard in the cardiac community. Fluoroscopy was set to a pulsed mode of 7.5 frames per second. Recording angiography was recorded at a rate of 15 frames per second. Collimation was not utilized, however, the physicians were encouraged to utilize standard shielding available in the laboratory. Catheterizations were routinely performed within a set of 7 angled views. For coronary evaluation this included left anterior oblique (LAO) caudal, LAO with cranial, straight anterior with cranial angulation, right anterior oblique (RAO) caudal and RAO with cranial angulation. Ventriculography was completed with straight RAO and LAO projections. Angles were optimized for the individual patient. The performing cardiologists were asked to wear 2 dosimeters (DMC 2000, Global Dosimetry Solutions Inc., Irvine, California) that utilized a silicon diode detector with a energy range of 50keV-6MeV and a linear response to 1000R/hr. The cardiologists wore the dosimeters on the outside of their sterile gowns at the level of mid-abdomen and outside the thyroid shield during the completion of angiographic procedures. These placement areas were chosen for their solid organs that may be most affected by radiation scatter (e.g., liver, kidneys, prostate, testicles and thyroid). The procedures were randomly assigned to either use of their standard of care, which included routine use of standard protection devices in the angiographic suite or additional use of the radiation protection table. If the patients went on to interventional procedures, the dosimeters were removed at the end of the diagnostic angiographic procedure. Patient body surface area, radiation fluoroscopic, and cine angiography run times were recorded for analysis.

Statistical Analysis

All variables are given as a mean ± standard deviation. ANOVA was used to determine the significance level of differences in several parameters.

Results

Twenty-six patients were randomized to standard of care while 24 patients were randomized to the use of the radiation protection table. Twelve different cardiologists performed measured procedures with a frequency of 1–8 procedures. The average fluoroscopy times were similar between the control group 1.86 (± 1.27) minutes and the protected group 2.47 (± 1.90) minutes. The number of cine angiographic runs was also the same at 10.36 (± 2.86) and 10.29 (± 2.35), respectively.  The results for the control group shows a statistically significant 54% reduction.

Discussion

The use of ionizing radiation and its association with harmful effects has been noted since the late 1800s.⁵ Though the risk to the patient of excessive intraprocedural radiation may be seen in direct tissue damage (nonstochastic) the risk to health care personnel is more likely to be from the development of malignancy (stochastic). Protection was thought to be adequate if one avoided the primary radiation beam. However, when an increase in the incidence of leukemia was noted in radiologists, recommendations were developed on radiation protection and measurements. These recommendations have continued to decline 5–10 fold since the 1930’s until an upper limit of acceptability was developed and utilized as the current occupational guideline.⁶

The recent release of the BEIR VII report now reconfirms the results of the BEIR V report indicating that there is no acceptable limit and all levels of radiation exposure increase the risk of the development of a malignancy.^4,7 Humans are exposed to ionizing radiation from both natural and man-made sources. Very high doses can produce damaging effects in tissues that may become evident in a matter of days. Late effects such as cancer can occur after even low-dose exposures. However, these late effects may take many years to develop. Although radiation exposure for health care workers has declined as awareness and technological advances have improved, personnel in areas such as interventional cardiology and radiology may approach or commonly exceed the limits previously believed to be acceptable.⁸ The BEIR VII report defines low doses as those in the range near zero up to about 100 millisievert (mSv). A chest X-ray delivers about 0.1 mSv or 10 mRem.

In the United States, individuals are exposed to average annual background radiation levels of approximately 3 mSv. Scientific models predict that approximately 1 in 100 individuals will likely develop solid cancer or leukemia from an exposure of approximately 100mSv.⁴ We show that even with conventional protective shielding, fluoroscopy alone during a cardiac catheterization emits 1–1.5 mRem/minute at the doctors’ waist level due to scatter emitted from the patient. Most protection garments utilize the protection of .5 mm lead protection. At this level 85–95% of radiation is blocked. Though apparently comforting, this passthrough of 5–15% radiation is significant over one’s career. With every 5 catheterization cases (50 mRem), the physician will receive approximately 2.5 mRem under the lead (lead considered 95% effective). At an average of 5 cases per day, the penetrating lead radiation exposure will be equivalent to approximately 60 chest-X-rays per year. Even without taking into account the ambient radiation exposure that all individuals are exposed to, the physician would be exposed to a cancer risk of approximately 1 in 100 in approximately 16 years of practice.

Our results are similar to what previous authors have described for a surgical radiation protecting shields and drapes.^10–13 However, these devices must be actively utilized and adjusted by the physician operator. With up to 50% of personnel, especially physicians, not routinely wearing their dosimeters, more passive protection systems appear to be needed. The radiation protection table utilized in this study is much more passive and less physician operator dependent. We utilized as many high volume interventional cardiologists as possible to closely simulate real world radiation exposure, utilizing current shielding and the potential advantage of utilizing increased shielding with a more passive system.

Summary

The increasing use of complex cardiac and endovascular procedures often require the physician and staff to be close to the area of scatter radiation for long fluoroscopic times. Given these demands, methods to reduce radiation beyond the standard shielding should be utilized. The results of this study show that with little expense and minimal adjustment in patient prepping, a significant reduction in scatter radiation exposure can be realized.

Limitations

The current study was only completed in cardiac above-the-hip angiography. The benefit may potentially be extrapolated for other above-the-hip angiography such as cerebral angiography, but further study is needed to quantify the potential benefit for peripheral procedures.

EDITORIAL COMMENTARY

Frank J. Criado, MD

This study reported by Silver and Botti is as important as it is timely. Radiation exposure has become almost “epidemic” at the present time as a result of the proliferation of fluoroscopy-mediated procedures. And this is no longer the province of just cardiologists and radiologists as vascular surgeons and many other specialists become involved in the performance of image-guided therapy. The study appears to show that their (relatively) simple and user-friendly protective table shield is capable of reducing scattered radiation exposure of the physician (and team) significantly – at least for above-the-hip diagnostic angiography and intervention. Impact on peripheral lower extremity procedure remains unstudied. Better yet, the device is “passive” and not dependent on compliance or cooperation on the part of the interventional team. The only requirement, of course, is that it needs to be made part of the table set-up for every procedure. The cost is likely to be minimal. Disadvantages of using the protective board were not discussed by the authors but are likely to be minimal (if any). I for one would like to try it — first perhaps during carotid interventions — to gauge its practicality. In the end, it sounds like a simple and important adjunct that will provide an additional layer of safety and protection for physicians exposed to radiation on a repetitive basis, almost every week of their lives. I would encourage the authors to study (and report on) applicability and effectiveness during lower extremity angiography and intervention.