Cath Lab Digest

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 (Figure 1).

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 (Figure 2) or additional use of the radiation protection table (Figure 3). 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. A value of p < 0.05 was considered statistically significant. All statistical analyses were performed using Statview software, version 5.0.1 (SAS Institute Inc., Cary, North Carolina).

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.