Radiation Dose Assessment of 99mTc-labeled Tetrofosmin in Patients Undergoing Rest-Stress Myocardial Perfusion Scintigraphy

Purpose: Tetrofosmin labeled with technetium-99m (99mTc) is a myocardial imaging agent. The goal of this research is to evaluate the differences between two methods for assessing radiation dose: internal dosimetry by using a dose calculation program and an analytical model based on patient's weight. Materials and methods: A biodistribution of 99mTc-Tetrofosmin as reported in the literature was used in OLINDA/EXM-1.0 (R) to estimate patient-specific absorbed and effective radiation doses on 91 adults (33 female, 58 male) who were undergoing 99mTc-Tetrofosmin 8 mCi-rest/ 17 mCi-stress myocardial perfusion imaging. The dosimetry results were compared to the values calculated from scaling by a power function of body weight the values of effective radiation doses for adults from 99mTc-Tetrofosmin rest/stress provided by the International Commission on Radiological Protection (ICRP) publication 106. Results: The mean effective doses estimated by dosimetry in female patients were 3.46 mSv and 5.91 mSv at rest/stress respectively. In male patients the mean effective dose estimated by dosimetry was 2.87 mGy at rest and 4.86 mGy at stress. For male and female patients of the same weight the dosimetry shows that the women's effective doses are about 17% higher than for men. The effective doses estimated in patients with a weight of 100 kg by the analytical method differed from those based on dosimetry by up to 40% in women and 30% in men at rest and 35% in women and 25% in men at rest. Conclusions: Even though the standard ICRP dose values are scaled by patients' weight, the effective dose for overweight patients are underestimated, more for female patients than for male patients because ICRP values correspond to an adult male. These underestimations are an important factor to consider if an approach based on differences in patient's weight is used to adjust the amount of activity to be administered.