MON-590 Outcomes Following Radioactive Iodine Therapy (RAI) in Hyperthyroid Patients with Grave’s Disease and Toxic Nodular Disease

Background: RAI is used as definitive treatment for hyperthyroidism, but administered activities vary between institutions. We used a fixed activity of RAI therapy for Grave’s disease (GD) and toxic multinodular goitre (TMNG), and calculated activity for toxic adenoma (TA). We reviewed treatment outcomes at one year. Methods: Thyroid function tests 1 year post RAI were reviewed retrospectively to asess outcome for 79 hyperthyroid patients divided into 3 etiological groups: those with GD treated with 200MBq, TMNG treated with 400 MBq and TA treated with calculated activity (50-434 MBq), between January 2012 and June 2017. 24 hour isotope uptake results were examined retrospectively to assess relationship to clinical outcome. Results: 48/79 patients had GD (60.8%%), 16/79 TMNG (20.2%) and 15/79 TA (19%). Patients with GD were younger (median 46 years) compared to those with TMNG and TA (median 62 and 59 years respectively). There were more females in both groups (85.5% female in GD, 93.7% in TMNG and 83.3% in TA). At one year post-RAI, more patients with GD were rendered hypothyroid 28/48 compared to TMNG and TA (62.5% vs. 18.75% vs. 53.33%) and fewer patients with GD were rendered euthyroid (25% vs. 46.6% vs. 53.3%) or had persistent hyperthyroidism compared to those with TMNG/TA (12.5% vs. 0% vs. 0%). 12/28 patients with GD who developed hypothyroidism had 24 hour uptake >60% and all patients with 24 hour uptake >60% became hypothyroid in GD and TMNG groups. Conclusion: We used low activity RAI (200 MBq) as treatment for GD, an activity below international recommendations, with comparable outcomes and cure rate 87.5%. All patients with 24 hour uptake >60% in GD and TMNG group developed hypothyroidism post RAI indicating that lower activity RAI should be considered to reduce risk of hypothyroidism.