Conjugate view gamma camera method for measuring activity in 131 I treatments

Abstract

A quantification method is developed to determine 131 I activity and its associated uncertainty using regions of interest from gamma camera images. Inside a neck phantom, a known activity source is  introduced to simulate thyroid remainders in thyroid differentiated cancer. The three parameters that define the accuracy of the method are: net count rates in ROI, the air calibration factor of the gamma camera  and the attenuation correction factor. In order to obtain net count rates, four methods for background subtraction are tested. The best procedure to follow is based in two energy windows acquisitions, which gives an activity result of 47 ± 5 µCi, in good agreement with the real activity value for the source, 46 ± 5 µCi.