@article {Bacher631, author = {Robin Bacher and Melanie Hohberg and Markus Dietlein and Markus Wild and Carsten Kobe and Alexander Drzezga and Matthias Schmidt}, title = {Thyroid Uptake and Effective Half-Life of Radioiodine in Thyroid Cancer Patients at Radioiodine Therapy and Follow-Up Whole-Body Scintigraphy Either in Hypothyroidism or Under rhTSH}, volume = {60}, number = {5}, pages = {631--637}, year = {2019}, doi = {10.2967/jnumed.118.217638}, publisher = {Society of Nuclear Medicine}, abstract = {Adjuvant radioiodine therapy (RITh) for differentiated thyroid carcinoma is performed either with thyroid hormone withdrawal or with administration of recombinant human thyroid-stimulating hormone (rhTSH). Heterogeneous results have been obtained on the impact of the method of patient preparation on thyroid uptake and whole-body effective half-life. A higher radiation exposure using thyroid hormone withdrawal for several weeks compared with rhTSH was reported in prior studies. It was the aim to examine whether these findings are reproducible in a modern protocol with a short interval between surgery and RITh. Methods: A retrospective study was performed on patients admitted for adjuvant RITh for differentiated thyroid carcinoma at the University Hospital of Cologne over a 5-y period from 2010. Dose rate measurements were analyzed for 366 patients, and subgroup analyses were performed for papillary thyroid cancer (n = 341) and follicular thyroid cancer (n = 25) patients, sex, length of hypothyroidism, and normal versus decreased glomerular filtration rate (GFR). Results: The median interval between surgery and RITh was 18 d for thyroid hormone withdrawal and 25 d for rhTSH (P \< 0.01). The mean thyroid uptake was 4.2\% {\textpm} 1.8\% for the 300 hypothyroid patients versus 3.8\% {\textpm} 1.6\% (P = 0.12) for the 66 rhTSH patients. Whole-body half-life in the hypothyroid group was significantly longer at 19.3 {\textpm} 7.7 h versus 16.4 {\textpm} 4.6 h in the rhTSH group (P \< 0.01). Results were predominantly influenced by data from the largest subgroup, that is, female papillary thyroid cancer patients. Within this group, whole-body half-life was significantly shorter in the rhTSH treatment arm. Duration of hypothyroidism and a decrease in GFR less than 60 mL/min/1.73 m2 significantly influenced results, with an increased whole-body half-life occurring in the hypothyroid group. When patients returned for whole-body scintigraphy, thyroid, half-life, and whole-body half-life were significantly shorter in the rhTSH groups, resulting in a low thyroid and remaining-body dose. Conclusion: With a shortening of the time between surgery and adjuvant RITh, thyroid uptake is not significantly changed but whole-body half-life becomes longer in the hypothyroid group. Radiation exposure for most patients is not significantly different. However, patients with a hypothyroid phase of more than 4 wk, and in particular those with a decreased GFR, experience higher radiation exposure.}, issn = {0161-5505}, URL = {https://jnm.snmjournals.org/content/60/5/631}, eprint = {https://jnm.snmjournals.org/content/60/5/631.full.pdf}, journal = {Journal of Nuclear Medicine} }