TY - JOUR T1 - rhTSH Stimulation Before Radioiodine Therapy in Thyroid Cancer Reduces the Effective Half-Life of <sup>131</sup>I JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 1065 LP - 1068 VL - 44 IS - 7 AU - Christian Menzel AU - Wolfgang T. Kranert AU - Natascha Döbert AU - Michaela Diehl AU - Thomas Fietz AU - Nadja Hamscho AU - Uwe Berner AU - Frank Grünwald Y1 - 2003/07/01 UR - http://jnm.snmjournals.org/content/44/7/1065.abstract N2 - Recombinant human thyroid-stimulating hormone (rhTSH) is effectively used for exogenous thyroid-stimulating hormone (TSH) stimulation before diagnostic 131I scintigraphy. It is not yet widely used for preparation of patients receiving a therapeutic amount of radioiodine. Methods: The results of 64 consecutive therapeutic applications of rhTSH with regard to clinical tolerance and side effects were evaluated in comparison with 163 radioiodine therapies (RITs) done on patients with hypothyroidism after thyroxine withdrawal during the same period. All therapies—applying 1.1–10 GBq of 131I—used a standardized protocol of patient preparation and activity application. RITs were followed by daily whole-body uptake measurements for 2–6 d, and a biexponential curve fit was used to obtain a short initial and afterward a long effective half-life of 131I. Patients after rhTSH were evaluated as a whole group (group A, n = 64) and as a subset of that group with normal thyroglobulin (hTG) levels (group D, n = 18). Patients after endogenous TSH stimulation were evaluated as a whole group (group B, n = 163), as a subset of that group excluding all ablative RITs (group C, n = 113), and as a subset of that subset with normal hTG levels (group E, n = 87). Results: rhTSH-stimulated patients showed significantly higher TSH values than did endogenously stimulated patients (P &lt; 0.001). Furthermore, the effective half-life of 131I was significantly prolonged after endogenous stimulation (e.g., 0.43 d for group A vs. 0. 54 d for group B, P &lt; 0.001). All rhTSH applications were tolerated well and without serious side effects. The only side effects were 2 cases of nausea and headache. Conclusion: The use of rhTSH for stimulation of TSH before RIT is safe but also significantly reduces the effective half-life of 131I. This is mainly due to a reduced renal iodine clearance in the hypothyroid state, but the bioavailability of radioiodine may be slightly overestimated because of larger amounts of intestinal 131I after endogenous TSH stimulation. ER -