Thyroid remnant dose: 124I-PET/CT dosimetric comparison of rhTSH versus thyroid hormone withholding before radioiodine remnant ablation in differentiated thyroid cancer.

AIM: Recombinant human thyroid-stimulating hormone (rhTSH) recently was approved as an alternative to thyroid hormone withholding (THW) to elevate TSH for thyroid remnant ablation in differentiated thyroid carcinoma patients. High ablation success rates are reported with diverse rhTSH-aided (131)I activities. Improved renal function causes approximately 50% faster radioiodine clearance under euthyroidism versus hypothyroidism. Knowledge of comparative remnant radioiodine kinetics, particularly the remnant radiation dose in Gy/GBq of administered (131)I activity (RDpA), could assist in choosing rhTSH-aided ablative activities. MATERIAL AND METHODS: To compare the RDpA, determined through (124)I-positron emission tomography/computed tomography (PET/CT), under the two stimulation methods, we retrospectively divided into two groups 55 consecutive totally-thyroidectomized, radioiodine-naïve patients. The rhTSH group (n=16) received (124)I on thyroid hormone, 24 h after two consecutive daily intramuscular injections of rhTSH, 0.9 mg. The THW group (n=39) received (124)I after weeks-long THW, when serum TSH first measured > or = 25 mIU/L. We performed PET investigations 4 h, 24 h, 48 h, 72 h and 96 h and PET/CT 25 h after (124)I administration. RESULTS: Median stimulated serum thyroglobulin was 15 times higher (p=0.023) and M1 disease almost twice as prevalent (p=0.05) in rhTSH versus THW patients. Mean+/-standard deviation RDpA was statistically equivalent between the groups: rhTSH, 461+/-600 Gy/GBq, THW, 302+/-329 Gy/GBq, two-sided p=0.258. CONCLUSIONS: rhTSH or THW deliver statistically equivalent radiation doses to thyroid remnant and may be chosen based on safety, quality-of-life, convenience and pharmacoeconomic factors. Institutional fixed radioiodine activities formulated for use with THW need not be adjusted for rhTSH-aided ablation.

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 patients2Gy 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.