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

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 oil 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 13 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 I ml at US evaluation had no effect on the ablation rate.