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
Robin Bacher, Melanie Hohberg, Markus Dietlein, Markus Wild, Carsten Kobe, Alexander Drzezga, Matthias Schmidt
Journal of Nuclear Medicine
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 to rhTSH was reported in prior studies. It was the aim to
... amine if these findings are reproducible in a modern protocol with a short interval between surgery and RITh. Method: A retrospective study was performed on patients admitted for adjuvant radioiodine therapy for differentiated thyroid carcinoma at the University Hospital of Cologne over a five-year period from 2010. Dose rate measurements were analyzed for 366 patients and subgroup analyses were performed for papillary (PTC, n = 341) and follicular thyroid cancer (FTC, n = 25) patients, gender, length of hypothyroidism and normal versus decreased glomerular filtration rate (GFR). Results: Mean interval between surgery and RITh was 18 days for thyroid hormone withdrawal and 26 days for rhTSH (p < 0.01). The mean thyroid uptake was 4.2 ± 1.8 % for the 300 hypothyroid patients versus 3.8 ± 1.6% (p = 0.12) for the 66 rhTSH patients. Whole-body half-life in the hypothyroid group was significantly longer at 19.3 ± 7.7 h versus 16.4 ± 4.6 h in the rhTSH group (p < 0.01). Results were predominantly influenced by data from the largest subgroup, i.e. female PTC patients. Within this group, wholebody half-life was significantly shorter in the rhTSH treatment arm. Duration of hypothyroidism and a decrease in GFR < 60 ml/min/1.73 m 2 significantly influenced results with 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. Conclusions: With a shortening of the time between surgery and adjuvant radioiodine therapy, thyroid uptake is not significantly changed but wholebody 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 weeks, and in particular those with a decreased GFR, experience higher radiation exposure.