Endocrine Abstracts

Introduction: Despite more than 60 years’ experience with radioactive iodine ¹³¹I (RAI) treatment of Graves’ disease (GD) about the most appropriate dosing regime is still controversial. The objective of our research was to analyse the outcome of RAI therapy in our cohort of patients.

Methods: Retrospectively, we analysed 603 patients with GD (500 women and 103 men, mean age 51.5±12.7 years) treated with RAI. According to recommended practice in Czech Republic, most patients came with at least 1-year history of the disease, in the first or next relapse. Their antithyroid medication was withdrawn 3–4 days before RAI administration. The treatment was considered successful if patients were euthyroid or hypothyroid on follow-up.

Results: Total efficacy of RAI treatment was 74% in 6 months and 88% in 12 months. We divided our cohort into three subgroups according the adjusted dose (adjusted to thyroid volume and 24-h RAI accumulation): i) in the first group (n=120) with adjusted dose 0.5–5.0 MBq/g the success rate was 54% in 6 months and 72% in 12 months, ii) in the second group (n=239) with adjusted dose 5.1–8.4 MBq/g it was 71 and 86%, and iii) in the third group (n=244) with adjusted dose 8.5–77.2 MBq/g it was 86 and 96% respectively. Median adjusted dose in the second group was 6.8 MBq/g. In the detailed analysis of the third group, any further dose increase over 8.5 MBq/g did not result in higher cure rates. In patients with higher thyroid volume (P<0.001) and higher disease activity (i.e. higher fT₃, fT₄, TSHR-Ab, and 24-h RAI accumulation as well as suppressed TSH), there was an increased risk of treatment failure. The therapy efficacy was not dependent on sex (P=0.580) and age (P=0.578).

Conclusion: With adjusted dose of 8.5 MBq/g, very reasonable efficacy was attained. In patients with smaller gland and lower disease activity it was possible to administer lower adjusted dose, ~6.5–7 MBq/g.