Graves' Disease Patients with Large Goiters Respond Best to Radioactive Iodine Doses of at Least 15 mCi: a Sonographic Volumetric Study

ABSTRACT

BACKGROUND AND OBJECTIVES: Radioactive iodine therapy (RAI) is an important treatment modality of Graves' disease (GD), but there is still not a consensus on the optimal dosage regimen. We studied the treatment success rate of different RAI doses, and examined which clinical markers were useful for determining the optimal RAI dosage for successful therapy in Korean patients. MATERIALS AND METHODS: We retrospectively studied 123 patients with GD treated with RAI between 2004 and 2014 at Chonnam National University Hwasun Hospital. The responder group was defined as patients who developed hypothyroidism requiring levothyroxine replacement following RAI, regardless of the RAI dosage. RESULTS: A total of 54 patients (43.9%) became hypothyroid after the first dose, and 31 needed two to four additional doses to achieve hypothyroidism. In the responder group as a whole (85 patients), the mean total dose of RAI was 15.5±7.0 mCi and the mean thyroid volume (TV) was 35.4±23.4 mL. When divided into low dose ( < 15 mCi, n=46) and high dose (≥15 mCi, n=39) responder groups, TV was significantly lower in the low-dose responder group (25.7±11.4 vs. 48.4±31.3, p < 0.001). The optimal cut-off TV for the low-dose responder group was < 32.37 mL (sensitivity 80.9%, specificity 76.7%). CONCLUSION: TV had significant effects on the outcome of RAI in GD patients. The optimal fixed RAI dose for Korean GD patients with a large goiter (≥33 mL) should be at least 15 mCi to achieve the best outcome.