Approach to the Patient: Role of Dosimetric RAI Rx in Children With DTC

Abstract

Pediatric differentiated thyroid cancer (DTC) patients frequently present with lymph node and/or distant (lung) metastases. Such patients warrant an aggressive treatment consisting of surgical removal of all surgically accessible local metastases as well as further treatment with one or more courses of radioiodine therapy (RAI). It is still a subject of debate in literature how much I-131 should be administered to pediatric patients. Patients can either be given a fixed (possibly body weight adjusted) activity or a dosimetry based activity, which is often considerably higher. Here, we will present a typical case of a pediatric patient who was treated using a dosimetric approach. Then we will discuss the basis of dosimetry and the procedures involved, followed by a discussion of when to use dosimetric RAI as well as the pros and cons of the various approaches in pediatric patients. In general, two opposite approaches to dosimetry exist: either the activity that is as high as safely administrable (AHASA) is determined based on the radiation exposure to the critical organs at risk (in pediatric patients these are the bone marrow and, in patients with lung metastases, the lungs), or a lesion-based approach in which the activity that is required to deliver a certain radiation dose to the metastatic lesion(s) is determined. Because the latter approach requires an accurate volumetry of the target lesion(s), which is not possible in children with disseminated pulmonary metastases, which are often not visible with morphologic imaging techniques, we advocate using the AHASA approach in children with extensive metastatic DTC.