Outcome of 131I therapy in hyperthyroidism using a 550MBq fixed dose regimen

Area of Science:

• Endocrinology
• Nuclear Medicine
• Thyroidology

Background:

• Radioiodine (131I) is a primary treatment for recurrent hyperthyroidism, but optimal dosing protocols remain unclear.
• Fixed-dose radioiodine therapy is gaining popularity, yet patient responses can vary significantly.

Purpose of the Study:

• To evaluate the effectiveness of a standard 550 MBq dose of radioactive iodine (131I) for hyperthyroidism treatment.
• To identify factors influencing the outcome of radioiodine therapy in a regional referral center.

Main Methods:

• A cohort of 449 hyperthyroid patients received a standard 550 MBq dose of 131I between 2003 and 2007.
• Patients were categorized by etiology (Graves' disease, toxic multinodular goitre, indeterminate).
• Antithyroid drugs were discontinued at least one week prior to radioiodine administration.

Main Results:

• One year post-treatment, 74% of patients became hypothyroid, 19% remained euthyroid, and 7% required re-treatment.
• Graves' disease patients were more likely to become hypothyroid (78%) and less likely euthyroid (11%) compared to toxic multinodular goitre patients (37% hypothyroid, 55% euthyroid).
• Higher initial free T4 levels (>80 pmol/L) and larger goitres were associated with increased treatment failure rates. Prior antithyroid medication also correlated with higher failure rates (8% vs 2%).

Conclusions:

• A single 550 MBq dose of 131I is a highly effective treatment for hyperthyroidism.
• Hyperthyroidism etiology, disease severity at diagnosis, goitre size, and prior antithyroid drug use significantly impact treatment outcomes.