A Randomized Controlled Trial to Evaluate the Effectiveness of 2 Regimens of Fixed Iodine (131I) Doses for Graves Disease Treatment

Aim: To investigate the effectiveness of 2 fixed iodine (I-131) doses for the treatment for Graves hyperthyroidism and their impact on eye disease. Methods: We prospectively examined 76 patients who received a fixed dose of 370 MBq (group 1) and 52 patients who received 555 MBq I-131 (group 2). Patients were followed up for 12 months and considered in remission when they were in a stable euthyroid or hypothyroid state in the absence of antithyroid drugs 12 months after I-131 administration. Eight patients with active eye disease received a daily dose of 0.5 mg/kg prednisone per kilogram of body weight at the time of radioiodine therapy for 1 month. Results: The remission rate obtained was similar in groups 1 (73.7%) and 2 (80.8%; P = 0.35). Hypothyroidism was diagnosed in 56.5% of the 370-MBq group and 71.1% of the 555-MBq group patients (P = 0.13). There was no correlation among clinical features, thyroid uptake, antibody levels, serum hormones levels, and outcome. However, logistic regression analysis demonstrated that patients with large thyroid glands had 2.4 times less chance to go into remission (odds ratio; 95% confidence interval = 1.18-4.96). None of the patients developed eye disease during any fixed-dose treatment regimen or worsened their previously diagnosed ophthalmopathy. Conclusions: Fixed doses of 370 MBq and 555 MBq I-131 provided similar remission rates; however, outcome was influenced by the thyroid size. We propose that 370 MBq I-131 should be the routine treatment dose for all Graves disease patients, reserving a dose of 555 MBq I-131 to palpable large goiters, without any additional concern to eye disease.