Evaluating the effectiveness of a fixed little dose of radioactive iodine (I131) in treatment for Graves' disease

Radioiodine (I-131) therapy is a clinically established method for hyperthyroidism treatment. The most suitable dose for successful treatment is still controversial since it is affected by several factors. Thus, there are two techniques for proper dose adjustment; Fixed and calculated. This study aims to evaluate the response difference of hyperthyroidism to a low fixed dose of 5 mCi (185 MBq) in comparison with other fixed doses of 10 mCi and 15 mCi (370 and 555 MBq) radioactive iodine treatment protocols. It also aims to raise the possibility of euthyroid state after successful ablation with such a low fixed dose rather than hypothyroid results and long-life replacement therapy. A prospective study of 100 patients were clinically and scintigraphically diagnosed with Graves' disease (GD) from the endocrinology department at King Faisal Medical Complex. The kind and size of the patient's thyroid were determined before treatment and then randomized into three groups, based on the administrated radio-active iodine dose, (5 mCi, Group I), (10 mCi, Group II) and (15 mCi, Group III). The thyroid function tests were performed after 3 and 6 months, as a follow-up, for the assessment of the outcome. Similar responses for fixed doses of 5, 10 and 15 mCi were determined, with no significant difference between the three study groups. Successful ablation was achieved in 23 (71.9%), 27 (84.4%) and 22 (71.0%) patients in the 5, 10, 15 mCi groups respectively without a significant difference between the groups with p-value of 0.695. Moreover, all considered related factors to the outcomes show no effect except the thyroid size with a p-value <0.001. The baseline size of the thyroid gland was significantly smaller in the Successful ablation group and the Euthyroidism group as compared to the Hyperthyroidism group (51.36 +/- 4.32 and 53.73 +/- 5.19 vs. 70.54 +/- 8.70; p < 0.001). Fixed little doses of 5, 10 or 15 mCi of I-131 show comparable remission rates. These outcomes were not affected by any factor related to the thyroid except thyroid size. Larger thyroid glands have less chance of remission. So, we envisage that a 5 mCi of radioactive iodine dose is recommended as a routine treatment for patients diagnosed with GD.