Predictive factors for the efficacy of radioiodine therapy in patients with Graves’ disease

Objective The primary treatments for Graves’ disease include antithyroid drugs (ATD), thyroidectomy, and iodine-131 (I-131) therapy. This study aimed to identify factors predicting treatment outcomes and the treatment period required to achieve euthyroidism after I-131 administration. Methods This study included 109 patients with Graves’ disease who underwent I-131 therapy. Patients achieving euthyroidism or hypothyroidism within 1 year were classified as the success group, whereas those with remaining hyperthyroidism were classified as the failure group. Thyroid volume, computed tomography (CT) values, 24-h radioiodine uptake, effective half-life, the levels of free triiodothyronine, free thyroxine, thyroid-stimulating hormone, and thyrotropin receptor antibody, history of I-131 therapy, history of ATD use, history of potassium iodide use, and thyroid absorbed dose were analysed. Results Larger thyroid volume [odds ratio = 0.982, 95% confidence interval (CI): 0.967–0.998, P < 0.05] was identified as a predictive factor for treatment failure, as determined by multivariable logistic regression. In contrast, a shorter treatment period was associated with lower thyroid volume (hazard ratio = 0.990, 95% CI: 0.982–0.999, P < 0.05), higher thyroid absorbed dose (hazard ratio = 1.007, 95% CI: 1.002–1.011, P < 0.01), and lower thyroid CT values (hazard ratio = 0.963, 95% CI: 0.939–0.987, P < 0.01), as identified by multivariable Cox regression. Conclusion Larger thyroid volume was associated with treatment failure. Smaller thyroid volume, higher thyroid absorbed dose, and lower thyroid CT values were significant predictors of the treatment period required to achieve euthyroidism after I-131 administration.