124-Iodine Positron Emission Tomography/Computed Tomography Dosimetry in Pediatric Patients with Differentiated Thyroid Cancer

Abstract

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 ≤18 yrs old.

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.

Key words

differentiated thyroid carcinoma - pediatric patients - 124-iodine positron emission tomography/computed tomography dosimetry - radioiodine treatment - recombinant human thyroid-stimulating hormone - thyroid hormone withdrawal - children - adolescents

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