Clinical outcome after standardized versus dosimetric radioiodine treatment of hyperthyroidism: an equivalence study

The aim of this study was to investigate the equivalence in outcome of standardized versus uptake-adjusted dosing of radioactive iodine (131I) for hyperthyroidism. We performed a 1-year follow-up study of two patient cohorts: 326 patients referred for 131I treatment of hyperthyroidism in Graves' disease (GD; n=216) or toxic multinodular goitre (TMG; n=110) in the period June 1995 to January 1998. Of these patients 128 were treated according to a standardized regimen, based on palpated thyroid volume and diagnosis, and 198 with a 131I uptake-adjusted dosimetric method. The incidence of hypothyroidism, euthyroidism or recurrence of disease was recorded. In Graves' disease hypothyroid outcome in the standardized versus adjusted method was 40.7% vs 44.6% (95% CI difference, -17.4 to +9.5%); it was 67.4% vs 70.8% (95% CI difference -15.9 to +9.3%) for all non-euthyroid outcomes. In TMG, due to wide confidence interval ranges a conclusion of equivalence could be made only for recurrence of hyperthyroidism (mean -3.2%, 95% CI, -13.8 to +7.5%). A simplified dosage method for 131I treatment of hyperthyroidism, which omits 131I uptake adjustment, may improve procedure efficiency and patient convenience, and leads to an equivalent outcome in GD and probable equivalent outcome in TMG.