Reduction in Occupational and Patient Radiation Exposure from Myocardial Perfusion Imaging: Impact of Stress-Only Imaging and High-Efficiency SPECT Camera Technology

Abstract

Recently introduced high-efficiency SPECT cameras have demonstrated the ability to reduce radiation exposure to patients undergoing myocardial perfusion imaging studies, especially when combined with stress-only imaging protocols. To date there have been no relevant studies examining the reduced occupational radiation exposure to medical staff. We sought to determine whether changes in stress myocardial perfusion imaging protocols and camera technology can reduce the occupational radiation exposure to the staff of a nuclear cardiology laboratory. Monthly radiation dosimeter readings from 4 nuclear technologists, 4 nurses, and 2 administrative employees were analyzed from two 12-mo periods: October 2007-September 2008 (period 1), before the use of high-efficiency SPECT, and October 2010-September 2011 (period 2), after high-efficiency SPECT was introduced. The average monthly dose equivalent in millirems (1 mrem = 0.01 mSv) was recorded from personal dosimeters worn on laboratory coats. The total activity of (99m)Tc used per month, mean (99m)Tc administered activity per patient, average number of patients per month, patient time spent in the laboratory, and proportion of stress-only studies were determined. There were 3,539 patients in period 1 and 3,898 in period 2. An approximately 40% reduction in the dose equivalent across all staff members occurred during this time (-16.9 and -16.2 mrem for nuclear technologists and nurses, respectively; P < 0.0001). During period 2, the total activity of (99m)Tc used per month decreased (10,746 vs. 7,174 mCi [1 mCi = 37 MBq], P < 0.0001), as did the mean (99m)Tc administered activity per patient (36.5 vs. 23.8 mCi, P < 0.0001). The percentage of patients having stress-only imaging increased (35% vs. 56%, P < 0.0001), and the total patient time spent in the laboratory decreased. Radiation dose equivalent levels were reduced in period 2 to 1%-7% of the allowed annual occupational dose equivalent. The combination of the use of high-efficiency SPECT technology and stress-only protocols resulted in a 34.7% reduction in mean total (99m)Tc administered activity between time periods, with camera technology being responsible for 39.2% of the reduction and stress-only protocols for 60.8%. A combination of high-efficiency SPECT technology and selective use of stress-only protocols significantly reduces the occupational radiation dose equivalent to the staff of a nuclear cardiology laboratory.