Success Rate of Radioactive Iodine Therapy in Graves’ Disease Using Dose Corrected for Thyroid Gland Size

Objective: Dose corrected for thyroid gland size is one of the methods used to determine I-131 activity for patients with Graves’ disease. This study aimed to find the success rate of this method and the predictors for successful I-131 treatment. Methods: This retrospective descriptive study conducted was in patients with Graves’ disease who received the first dose of radioactive iodine (RAI) therapy. Patients received a fixed RAI dose of either 10, 15, 20, 25, or 30 mCi for corresponding thyroid gland size of ≤ 50, 51-100, 101-150, 151-200, and >200 grams, respectively. The treatment outcome assessed was between 6 to 9 months after the therapy based on serum free thyroxine and serum thyroid stimulating hormone. Successful treatment was defined as euthyroid and hypothyroid. Results: A total number of 179 patients (126 females; mean age: 40.8 years) were enrolled. There was one patient exclusion from the outcome analysis due to undetermined laboratory results. The success rate of RAI therapy was 50% (95% CI: 42.4-57.6). Patients with gland size ≤ 50 gm had the highest success rate of 59.6%. Multivariable analysis showed no significant association between sex, thyroid gland size, prior antithyroid drug use and successful treatment. Conclusion: First RAI therapy using dose corrected for thyroid gland size had a modest success rate of 50% in patients with Grave’s disease. Sex, thyroid gland size, and prior antithyroid drug use were not significantly associated with the treatment outcomes.