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

Aim: 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.

Methods: 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.

Results: 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.

Conclusions: 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.