Validation of 131I activity in thyroid phantom using SPECT/CT 3D image based dosimetry

Abstract

Quantitative imaging gives a better understanding on the distribution of radioactivity that can be used in the estimation of absorbed dose in the specific target organ. The goal of this study was to validate the accuracy of 131I activity quantification of cumulated activity in thyroid uptake phantom using 3-dimensional (3D) SPECT/CT imaging. In this study, a series of SPECT/CT acquisition of the thyroid uptake was performed. Images of different matrix sizes and iterations number were reconstructed using ordered-subsets expectation maximization (OSEM). Quantification of the activity in the phantom was determined using a Medical Image Data Examiner (AMIDE) software based on the mean value and maximum value. The cumulated activity in the phantom was determined by calculating area under the curve (AUC) in the time-activity curve. The results showed that the mean activity for 256 voxels was underestimated between 6.18% - 13%, and overestimated between 61.56% - 64.66% for maximum value metric. The cumulated activity derived from SPECT/CT showed an error margin of 10%.