Evaluation of whole-body retention of iodine-131 ((131)I) after postoperative remnant ablation for differentiated thyroid carcinoma - thyroxine withdrawal versus rhTSH administration: A retrospective comparison.

Previous studies demonstrated that preparation with recombinant human thyroid-stimulating hormone (rhTSH) for thyroid remnant ablation results in lower extrathyroidal radiation compared to hypothyroidism. The results of 50 radioiodine therapies (RITs) under rhTSH, regarding iodine half-life, were evaluated and compared with 50 RITs performed on patients with hypothyroidism following thyroxine withdrawal. The patients were treated with 3700 MBq (100 mCi) of (131)I. Forty-eight hours after RIT, patients were measured with a radiation detector at a 1-meter (m) distance for evaluation of the effective dose (μSv/h). TSH and thyroglobulin (Tg) maximal values were also compared. rhTSH-stimulated patients had a significantly lower whole-body retention of (131)I (8.5±7.3 μSv/h), extrapolated from the measurements of the effective dose at a 1-m distance, compared to endogenously stimulated patients (13.6±8.1 μSv/h; p=0.001). Furthermore, TSH mean and Tg median levels were significantly higher in the rhTSH-stimulated patients (89.9±15.3 mU/l and 7.7 ng/ml, respectively) compared to the hypothyroid group (59.2±25.1 mU/l and 3.3 ng/ml; p<0.001 and p=0.003, respectively). Compared to thyroid hormone withdrawal, the use of rhTSH prior to RIT was associated with significantly lower whole-body retention of (131)I and with greater efficacy in reaching TSH levels greater than 30 mU/l, confirming data previously described.