Outcomes Following Fixed Dose Radioactive Iodine Therapy (RAI) in Hyperthyroid Patients with Grave’s Disease and Toxic Nodular Disease

Abstract

Background: Radioactive iodine (RAI) is a definitive treatment for hyperthyroidism, but administered doses vary between institutions. We utilize a fixed dose RAI treatment protocol, administering 370MBq to all patients unless there is a large goitre present. We aimed to determine treatment outcomes following fixed dose RAI at our centre. Methods: We retrospectively reviewed thyroid function at 1 year following RAI therapy in 166 consecutive hyperthyroid patients who had been treated with 370MBq RAI between January 2001 and March 2015. Patients were stratified into 2 aetiological groups: Grave’s disease (GD) and toxic multinodular goitre (TMNG)/toxic adenoma (TA) for comparison. Results: 166 patients received 370MBq RAI over the period specified. 88 patients had GD (53%) and 70 patients had TMNG/TA (42%). Aetiology was not specified in 8 patients (5%). Patients with GD were younger 46.1±1.5 years (mean±SEM)) compared to those with TMNG/TA (63.3±1.4 years, p<0.001) and there were more female than males in both groups (80% female in GD and 84% in TMNG/TA, p=0.445). At one year post-RAI, more patients with GD were rendered hypothyroid compared to TMNG/TA (55% vs. 17%) and fewer patients with GD were rendered euthyroid (34% vs.63%) or had persistent hyperthyroidism compared to those with TMNG/TA (11% vs 20%) (p<0.001). Conclusion: When compared to GD group, proportionally more TMNG/TA patients remained hyperthyroid a year following a single dose of 370Mbq RAI. TMNG/TA patients were more likely to be euthyroid at one year post RAI, however. These results suggest that a higher dose of RAI may be needed for TMNG/TA.