Low-activity (2.0 GBq; 54 mCi) radioiodine post-surgical remnant ablation in thyroid cancer: comparison between hormone withdrawal and use of rhTSH in low-risk patients

Abstract

Objective(a) To compare the efficacy of low-activity (2 GBq; 54 mCi) 131I ablation using l-thyroxine withdrawal or rhTSH stimulation, and (b) to assess the influence of thyroid remnants volume on the ablation rate.DesignPatients underwent neck ultrasound, 131I neck scintigraphy and radioiodine uptake. Post-therapy whole body scan (WBS) was acquired after 4–6 days. Ablation was assessed after 6–12 months by WBS, Tg and TgAb following l-thyroxine withdrawal.MethodsGroup A: preparation by L-T4 withdrawal (37 days); 21 patients received 131I (2.02±0.22 GBq; 54.6±5.9 mCi) and on the day of treatment, TSH, Tg, TgAb were measured; Group B: stimulation by rhTSH; 21 patients received 131I (1.97±0.18 GBq; 53.2±4.9 mCi) 24 h after the second injection of rhTSH (0.9 mg) and TSH, Tg and TgAb were measured after 2 days.ResultsAt follow-up, 90.0% of patients from group A and 85.0% of patients from group B had Tg levels <1 ng/ml; no uptake was observed in 95.2% and in 90.5% of patients from group A or B respectively, with no statistical differences for both ablation criteria. Before 131I treatment, small thyroid remnants (<1 ml) were detected by US in <25% of all patients.ConclusionsThe use of rhTSH for the preparation of low-risk patients to ablation therapy with low activities of 131I (2 GBq; 54 mCi) is safe and effective and avoids hypothyroidism. The presence of thyroid remnants smaller than 1 ml at US evaluation had no effect on the ablation rate.