RESUMO
BACKGROUND: There is no standardized approach to iodine-131 (I-131) therapy of hyperthyroidism in pediatric Graves disease. This prevents systematic study of outcomes. OBJECTIVE: To characterize current radioiodine dosing and define therapeutic outcomes at multiple institutions that use ultrasound to measure thyroid size to guide I-131 ablation of Graves disease. MATERIALS AND METHODS: This was a retrospective cohort study conducted at three institutions. The three sites collected demographic data, thyroid volume measured by ultrasound (mL), pre-ablation radioiodine uptake, I-131 activity administered, and outcomes at 6 and 12 months for children younger than 18 years of age treated with I-131 between November 2004 and October 2019. Comparisons of continuous variables were performed using the Mann-Whitney U test. RESULTS: Sixty-nine patients (mean age: 14.5±2.5 years) were included, 59 (85.5%) of whom were female. The mean administered I-131 radioiodine activity was 12.5 mCi (463 MBq) (range: 3.8-29.9 mCi [141-1,106 MBq]). At 6 months post-ablation, 54 (80.5% of 67) patients were hypothyroid, 8 (11.9% of 67) were euthyroid and 5 were hyperthyroid. Two of the five hyperthyroid patients had become euthyroid at 12 months. At 12 months, 1 previously euthyroid patient was hyperthyroid. Administered activity per mL of thyroid tissue adjusted for 24-h uptake was lower (0.18 mCi [6.7 MBq] x %/mL vs. 0.31 mCi [11.5 MBq] x %/mL, P=0.0054) for patients who remained hyperthyroid at 6 months. CONCLUSION: There is substantial variability in administered activity for radioiodine ablation of Graves disease in children. Efforts to standardize practice should start by standardizing administered activity guided by measurement of thyroid size by ultrasound. Our results and those of previous studies suggest the need for administered activities ≥0.25 mCi [9.3 MBq] x %/mL of thyroid tissue.