Efficacy of Single Fixed Dose of Radioiodine (I 131) Therapy in Patients Treated for Hyperthyroidism at Nuclear Medicine Department of Groote Schuur Hospital(GSH).

BACKGROUND Failure of radioactive iodine therapy (RAI) in patients with hyperthyroidism is not uncommon. A Second dose is usually needed if the first one failed. The purpose of this audit was to determine the efficacy of RAI in patients with hyperthyroidism at Groote Schuur Hospital (GSH). METHODS This was a retrospective study. A single observer reviewed the records of all patients who received I131 therapy for hyperthyroidism between 23rd April, 2010 and 23rd November, 2017 in conjunction with their pre- and post-treatment thyroid function tests. Results of their thyroid ultrasound were retrieved and documented. The images of their Tc99m sodium per-technetate thyroid scans were also retrieved and reprocessed. Cure was determined by three consecutive thyroid function tests by euthyroid or hypothyroid status 6 months after therapy. RESULTS Of the 353 patients with complete records, 310 (88%) of our patients were females and 43 (12%) were male patients. Majority (200 patients) of the patients were older than 45 years of age, 148 patients were between 15 to 45 years and 5 patients were 5 years and below. 314 patients (89%) achieved cure at some stage after receiving one dose of RAI; 239(76%) achieved cure < 6 months of therapy and 75(24%) patients after 6 months. Patients who failed to achieve cure following the first RAI therapy appeared to be younger (median(interquartile range) age 39(16), p=0.03), had severe hyperthyroidism as demonstrated by higher pre-treatment FT4 (median(interquartile range) 27 pmol/L(30.6), p= 0.05) and high pertechnetate uptake (median(interquartile range) uptake 9.9%(14), p= 0.002) on thyroid scintigraphy. CONCLUSION Our audit showed cure rate was 68% at 6 month and 89% at a year. A second dose was indicated in 32% of patients. Patients presenting with severe thyrotoxicity are likely to require more than one RAI therapy. Further researches are suggested to find out if pre-treatment with antithyroid drugs would influence efficacy of RAI in patients with severe thyrotoxicity and would a one year follow up after radioiodine therapy be considered before second RAI.