Comparison of 30- and 50-mCi Doses of Iodine-131 for Thyroid Ablation

Abstract

We compared the utility of lower (30 mCi) and higher (50 to 60 mCi) doses of ¹³¹I used to ablate residual thyroid tissue after thyroidectomy for carcinoma. Whole body scans were done using 1 mCi ¹³¹I, 3 weeks after withdrawal of triiodothyronine. Patients had received ablation therapy within 3 days after scanning, and one or more subsequent scans were analyzed. Forty-eight patients were treated to ablate residual thyroid tissue that was presumed to be normal. Among 18 patients given the lower dose of ¹³¹I as outpatients, 15 had successful ablation and three needed a second administration; all 30 patients treated with the higher dose had successful ablation. Seventeen additional patients, presumed to have residual cancer, received 50 to 150 mCi; and six needed treatment. Although 1 dose of 50 to 60 mCi ¹³¹I provides more certain ablation, use of the usually effective 30-mCi dose for initial ablation is justified by the convenience of outpatient administration, the lower expense, and the lower whole-body radiation dose.