Dose‐Dependent Efficacy of Radioiodine Therapy in Pediatric Graves’ Disease: A Retrospective Study of Hypothyroidism Risk and the Predictive Role of Thyroid Hormone Parameters

ABSTRACT Background Outcomes of radioactive iodine therapy in pediatric Graves' disease vary. This study aimed to evaluate the efficacy of radioactive iodine therapy and identify prognostic factors. Methods We retrospectively analyzed 156 pediatric patients with Graves' disease treated with radioactive iodine therapy between 2012 and 2022 with ≥ 1 year of follow‐up. Multivariate least absolute shrinkage and selection operator regression identified efficacy predictors. Outcomes were compared by planned activities (≥ 0.15 mCi/g vs. < 0.15 mCi/g) and thyrotrophin receptor antibody concentrations. Results Success rates rose from 60.1% (86/143) (3 months) to 79.3% (73/92) (12 months), and hypothyroidism increased from 39.9% (57/143) to 54.3% (50/92). Free triiodothyronine and thyroid‐stimulating hormone concentrations were identified as key predictors of efficacy. A higher treatment success rate was observed with planned activity ≥ 0.15 mCi/g (76.2% vs. 49.4%), although the difference was not statistically significant after Bonferroni correction (adjusted p = 0.056). Higher thyrotrophin receptor antibody concentrations showed a nonsignificant trend toward lower success of therapy. Conclusions Radioactive iodine shows time‐dependent efficacy in pediatric Graves' disease. Free triiodothyronine, thyroid‐stimulating hormone, and planned radioactive iodine activity were associated with treatment outcomes in this cohort. Higher planned activities were associated with higher cure rates but also an increased risk of hypothyroidism. These exploratory findings require prospective external validation before being applied to individualized treatment planning.