Variation in Thyroid Calibration Efficiencies as a Function of Phantom Design for I-125

摘要

Four commercially available thyroid phantoms were evaluated to determine the effect that choice of phantom would have on the determination of I-125 activity in the thyroid. Efficiency calibration values for a 5.0-cm diameter 1-mm thick NaI (Tl) detector were determined as a function of distance from the phantom along the central axis and at angles up to 45 off axis using I-125 as the radionuclide of interest. Results indicate that substantial variations in the estimate of radioactivity in the thyroid will occur based on choice of calibration phantom. Using the Humanoid System, Inc. Realistic Phantom as the reference phantom, one could experience differences in estimated activity in the human thyroid that range from 0.86 to 2.94. 6 refs., 6 figs., 3 tabs. (ERA citation 12:046710)