124-iodine positron emission tomography/computed tomography dosimetry in pediatric patients with differentiated thyroid cancer.

Aim: Publications on 124-iodine (124I-)-positron emission tomography/computed tomography (PET/CT) dosimetry contain few if any data on pediatric patients with differentiated thyroid carcinoma (DTC). Aim of our study is to determine safety and informativeness of 124I-PET/CT dosimetry in DTC patients
Material And Methods: We retrospectively analysed the data of 3 years of consecutive procedures (n-5) in children (n-4, 11-15 years). We acquired whole-body 124I-PET emission data 4, 24, 48, 72 and 96 hr, and 124I-PET/CT data 25 hr after oral 124I administration (22-26 MBq). Using these data, we calculated the thyroid remnant or metastatic lesion dose in Gy per GBq of 131-iodine (131I) (RDpA or LDpA, respectively). We measured with a well counter radiation counts of blood samples taken at 2, 4, 24, 48, 72 and 96 hr, and with an uncollimated NaI detector, whole-body clearance at approximately those times. Using these data, we calculated each patient's critical blood activity (CBA), the maximum 131I activity avoiding the putative>2Gy blood dose portending serious myelotoxicity.

Results: Besides hypothyroid fatigue, no symptoms were noted. In 4 dosimetry procedures before the first radioiodine therapy, RDpAs were generally high (median 288 Gy/GBq, range 59-648 Gy/GBq). LDpAs (4 lymph node metastases) were much lower (median 6.5 Gy/GBq, range 1-9 Gy/GBq). CBAs were high (median 26 GBq, range 19-42, n=5). Disease management was modified or disease extent clarified in 2/4 patients.

Conclusions: A standard adult 124I-PET/CT dosimetry protocol appears to be safe and informative in pediatric DTC patients.