Comparison of 30- and 50-mCi doses of iodine-131 for thyroid ablation

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 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.