A STUDY OF A CALIBRATION TECHNIQUE FOR A NEWLY DEVELOPED THYROID MONITOR AND ITS UNCERTAINTIES DUE TO BODY SIZE FOR RADIOIODINE MEASUREMENTS

Abstract We have developed a portable thyroid monitoring system to measure thyroid doses for members of the public in a nuclear emergency. It is assumed that a large number of these monitoring systems are deployed and maintained for emergency situations. Hence, the calibration performed should be performed as simple as possible. We proposed a new calibration method based on standard voxel phantoms using a point source. By applying this method to the thyroid monitoring system, the counting efficiencies were evaluated. Although this monitor is properly calibrated, any differences between the phantoms used in the calibration and the monitored subjects can affect the measurement accuracy. Therefore, the influence of the anatomical features of the subjects on the detection efficiencies was investigated in detail by Monte Carlo calculations. The effects of the body size on the counting efficiencies of the thyroid monitoring system were estimated using several voxel phantoms. Consequently, the uncertainties in the counting efficiencies due to the body size were found to be within 25 %.