Recombinant Human Thyroid Stimulating Hormone in Thyroid Remnant Ablation With 1.1 GBq 131Iodine in Low-Risk Patients

Objective: To evaluate the efficacy of recombinant human thyroid stimulating hormone [rhTSH (versus hypothyroidism)] in thyroid ablation with an activity of 1.1 GBq (30 mCi) I-131. Methods: A total of 102 patients with thyroid cancer who fulfilled the following criteria were studied: submitted to total thyroidectomy with complete tumor resection; tumor <= 4 cm without extrathyroid invasion or lymph node metastases; negative anti-thyroglobulin (anti-Tg) antibodies. Thirty-two patients (group A) received 0.9 mg of rhTSH for 2 consecutive days followed by I-131 administration and 70 patients (group B) were prepared by levothyroxine withdrawal for 4 weeks. The groups were similar in sex, age, and tumor characteristics. Results: Ablation was successful (stimulated Tg<1 ng/mL and negative diagnostic whole-body scanning and neck ultrasonography 9 to 12 mo after ablation) in 27 patients of group A (84.3%) and in 58 of group B (83%). Considering patients with Tg greater than 1 ng/mL immediately before I-131 administration, the rates were 72.2% in group A and 75% in group B. In group A, the ablation rate was similar for patients who discontinued levothyroxine-T4 3 days before I-131 administration and those maintained on hormone therapy. The mean follow-up was 29.6 months in group A and 55 months in group B. Stimulated Tg (after rhTSH) was undetectable in 29 patients of group A (90.6%) and in 61 of group B (87%) and 1 patient of group B presented cervical metastases at the last assessment. Conclusions: Low I-131 activity after rhTSH is effective for remnant ablation in patients who are at low risk of recurrence.