The effectiveness of 124I PET/CT in patients with differentiated thyroid cancer

Several studies consider 124I PET useful in the evaluation of differentiated thyroid cancer (DTC). The aim of this work was to evaluate the usefulness of 124I positron emission tomography (PET)/computed tomography (CT) for: 1) pretherapeutic staging; 2) optimizing the administering activity in case of remnants ablation; 3) individualizing a complex dosimetry case by case especially in plurimetastatic patients.

A total of 69 patients were studied in our department between September 2007 and June 2008: 17 male and 52 female, aged 17-83 (mean age 46.6) and, with a simplified method, an expectation dose with a distant therapeutic evaluation, in term of efficacy, was calculated. A total body 124I PET/CT and a whole body scan (WBS) were done, respectively, before and after radiometabolic therapy with 131I and then compared in double blind in 67/69. In 2/69 with a follicular plurimetastatic DTC (both female, aged 65 and 71), an individualized complex dosimetric study was done.

PET/CT and WBS matched in 58/67 patients (86.6%). We obtained a complete ablation of the thyroid remnants in 60/67 patients (90%). The individualized complex dosimetry tells us that the administrable maximum activity is for: patient 1:13320 MBq and patient 2:9250 MBq.

Iodine-124 PET/CT is a powerful diagnostic tool before administration of 131I therapeutic dose. It allows for a precise dosimetry in plurimetastatic patients. After an empiric dose estimation, the successful percentage in term of thyroid's remnants ablation was very elevated.