Low Dose Radioactive Iodine Treatment in Hyperthyroidism: Experience in a Medical Center in Northern Taiwan

Purpose: The study was designed to investigate the success rate of low dose radioactive iodine (RAI) treatment for hyperthyroidism and compare the outcomes between patients receiving lower dose and higher dose therapy. Methods: One hundred and seven patients who received first time RAI for hyperthyroidism and had a follow-up period for at least six months were retrospectively studied. Normal thyroid-stimulating hormone (TSH) and thyroxine (T4) levels were used to define successful treatment. Patients who received two or more doses of RAI or had abnormal TSH and/or T4 values were considered as having treatment failure. Success rate and status of subclinical or clinical hyperthyroidism were compared using chi-square between treatments with lower dose (3~5 mCi radioiodine) and higher dose (6~8mCi radioiodine). Results: The overall success rate was 36% and there was no difference in the success rates between the lower dose and the higher dose treatments. However, for patients with treatment failure, the odds of having subclinical instead of clinical hyperthyroidism was higher in those receiving lower dose RAI than those receiving higher dose RAI. Conclusion: A lower dose of 3~5mCi RAI is as effective as a higher dose of 6~8mCi RAI for the treatment of hyperthyroidism and may more likely result in subclinical instead of clinical hyperthyroidism even if the treatment fails. Accordingly, the lower dose RAI may be a better choice when treating hyperthyroidism with fixed low dose method due to the similar efficacy and possible more favorable outcome.