# Outcomes of Fixed-Dose Radioactive Iodine Therapy in Hyperthyroidism and Optimization of Follow-Up After Treatment Failure With Low-Dose Antithyroid Medication

## TL;DR

This study examines the effectiveness of fixed-dose radioactive iodine therapy for hyperthyroidism and suggests extended follow-up for patients on low-dose medication after treatment failure.

## Contribution

The study provides insights into optimal follow-up strategies for hyperthyroid patients after initial RAI treatment failure.

## Key findings

- 52% of patients achieved remission within six months post RAI.
- Extended follow-up showed 37.5% of patients remained euthyroid on low-dose ATDs.
- 45.8% of patients required a second RAI treatment after nine months.

## Abstract

Introduction: Fixed-dose radioactive iodine (RAI) therapy is a common treatment for hyperthyroidism. However, the optimal follow-up duration and management strategies for patients experiencing treatment failure remain uncertain. This study evaluates the outcomes of fixed-dose RAI therapy in hyperthyroid patients and explores the appropriate follow-up duration for those requiring low-dose antithyroid drugs (ATDs) after initial treatment failure.

Methods: A retrospective cohort study was conducted, including 204 hyperthyroid patients who received their first fixed-dose RAI treatment at Ratchaburi Hospital, Na Muang, Ratchaburi, Thailand, between December 2022 and May 2024. Treatment outcomes were assessed six months post RAI. Among the 98 patients with treatment failure, those who remained euthyroid on low-dose ATDs were followed for up to nine months to evaluate long-term outcomes. The study analyzed remission rates, progression to hypothyroidism, and the need for additional RAI therapy using descriptive statistics and Kaplan-Meier survival analysis.

Results: Of the 204 patients, 106 (52%) achieved remission within six months post RAI. Among the 201 patients with Graves' disease, 104 (51.7%) achieved remission. Of the 98 patients with treatment failure, 40 remained euthyroid on low-dose ATDs. After nine months of extended follow-up, nine (37.5%) maintained euthyroid status, four (16.7%) developed hypothyroidism, and 11 (45.8%) required a second RAI treatment. The median time to treatment failure was 6.9 months, suggesting that some patients may stabilize without immediate re-treatment.

Conclusion: RAI therapy is effective for hyperthyroidism. Extended follow-up without rushing to a second RAI dose may be sufficient for patients who remain euthyroid on low-dose ATDs, helping reduce unnecessary radiation exposure. However, further prospective studies are needed to establish guidelines for optimal follow-up and re-treatment timing.