Comparison of Thyroid Size-Specific Radioiodine Dose and New Modified Dose Calculation in the Treatment of Graves' Disease.

Backgruound: Previous studies of fixed-dose radioiodine therapy (RIT) for Graves' disease (GD) have utilized a variety of techniques and reported differing success rates. This study sought to compare the efficacy of RIT using two fixed-dose protocols and to estimate the optimal radioiodine (RAI) activity for the treatment of GD.

Methods: This retrospective trial enrolled 658 patients with GD who received RIT between January 2014 and December 2021. Participants were divided into two groups: protocol 1, which utilized a thyroid size-specific RAI dose, and protocol 2, which employed a modified dose calculation approach. The primary outcome assessed was the presence of euthyroidism or hypothyroidism at the 6-month follow-up. The success rates of RIT were compared between the two protocols.

Results: The RIT success rate was marginally lower for protocol 2 than for protocol 1 (63.6% vs. 67.2%); however, the risk of treatment failure did not differ considerably between the groups (relative risk, 1.1089; 95% confidence interval, 0.8937 to 1.3758; P=0.3477). The median RAI activity associated with protocol 2 was lower than that for protocol 1 (10.7 mCi vs. 15.0 mCi, P=0.0079), and the frequency of hypothyroidism was significantly lower in the protocol 2 group (39.0% vs. 48.9%, P=0.0117).

Conclusion: The success rate of the modified dose calculation protocol was comparable to that of the thyroid size-specific RAI dose protocol. The former approach reduced RAI activity and the incidence of hypothyroidism following RIT without compromising the success rate.