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) (131)I ablation using l-thyroxine withdrawal or rhTSH stimulation, and (b) to assess the influence of thyroid remnants volume on the ablation rate.

Design: Patients underwent neck ultrasound, (131)I 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.

Methods: Group A: preparation by L-T(4) withdrawal (37 days); 21 patients received (131)I (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 (131)I (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.

Results: At 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 (131)I treatment, small thyroid remnants (<1 ml) were detected by US in <25% of all patients.

Conclusions: The use of rhTSH for the preparation of low-risk patients to ablation therapy with low activities of (131)I (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.