Dosimetric methodology for 131I therapy for benign thyroid diseases

Abstract

Treatment with 131I is one of the standard treatments for benign thyroid disease. In most cases, the prescribed dose is specific for the same disease. Inspired by external radiotherapy, the emergence of personalized pre-therapeutic dosimetry in nuclear medicine departments makes it possible to adapt to the patient's diseases and physiology; more specific to its kinetics of iodine distribution. By personalizing the prescribed activity, dosimetry makes it possible to comply with the ALARA principle in metabolic radiotherapy while at the same time preserving the therapeutic objective. Post-treatment dosimetry permits to validate the methodology and, by recording the dose actually delivered to the organs surrounding the target volume, to contribute to the understanding of the dose-effect relationship. A re-reading of the MIRD formalism guidelines is important as this document lists the procedure to be followed in thyroid dosimetry. Defining the sensitivity, calculating the S factors, estimating the cumulative activity and residence times and then calculating the dose are the different steps presented. The need to switch from fixed dose prescription to personalized prescription seems to be evident. Several studies in progress as well as the emergence of new software compiling all the information essential for its implementation will permit nuclear medicine departments to involve themselves more easily into the process.