Abstract. Objective: Radioactive iodine-131 (RAI or 131I) has been established as effective in the treatment of patients with various etiologies of hyperthyroidism. However, the short-term and long-term clinical outcome of patients receiving RAI differs in various studies. The aim of this study was to assess the clinical outcome one year after RAI therapy and identify factors associated with a good response. Methods: In this experimental study, 164 patients were included. They were randomly selected from patients referred to the Nuclear Medicine Department for Graves’ disease, multinodular goiter, or toxic adenomas, which are indications for RAI therapy. The radioiodine dose was calculated based on the size of the thyroid gland by physical examination. Patients with normal thyroid glands were administered less than 10 mCi; patients with large thyroid glands or thyroid nodularity were administered a dose of greater than 10 mCi (approximately 15 mCi). Patients were monitored closely clinically and with blood investigations after treatment for one year. Results: Among 158 patients who completed follow up, 98.8% recovered and 1.2% remained thyrotoxic. Among patients who recovered, 74.2% became hypothyroid and 22.6% euthyroid. The incidence of hypothyroidism was 23% in first trimester, 43.7% in second trimester, 4.4% in third trimester, and 3.1% in forth trimester. Conclusion: In our study, a good result was seen in more patients than in other studies. The better outcome may be related to higher absorption of radioactive iodine in our region. The highest incidence of hypothyroidism was in the second trimester, so we recommend that patients should be carefully followed in this posttreatment period.

Keywords • Hyperthyroidism • Graves’ disease • Radioiodine therapy • Outcome • Hypothyroidism

Shinto, A.S., Pachen, L., Sreekanth, T.K.: Fixed Dose Radioactive Iodine Therapy in Hyperthyroidism: Outcome and Factors Affecting it in a Region in South India. Thyroid Science, 5(6):CLS1-7, 2010.

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