A new method to evaluate the residual activity in patients undergoing (131)I thyroid therapy

The radioiodine administration is a standard therapeutic approach to both benign thyroid diseases, such as hyperthyroidism, and carcinomas. The high administered (131)I activities are of radiation protection concern, due to relevant patient residual contamination. The aim of this work was to develop a new procedure based on external radiometric surveys and on a mathematical model in order to estimate the (131)I activity in patients undergoing hyperthyroidism radioiodine therapy. In the first stage of this study, a suitable detector was chosen and its response vs. activity was characterized. The experimental verification was performed measuring the ambient dose equivalent rate from patients receiving radioiodine administration. The results confirm the reliability of the proposed method, as shown by the slight differences between the administered activities and the ones calculated from external measurements. Furthermore, the same procedure was applied to detect the percentage residual activity in patients at two preset time intervals: 4 hours and 4 days after the radioiodine administration. The obtained results clearly highlight that the method can ensure a level of reliability compatible with the radiation protection purposes.