Background and aim: Fixed dose radioiodine therapy (RAI) is considered to be the standard regime for management of hyperthyroidism although the actual RAI activity used varies between different centres. We have undertaken a retrospective comparison between various outcomes achieved following the use of fixed RAI doses of 400 and 550 MBq at two different centres.
Patients and methods: An electronic database has been prepared for all patients who receive RAI therapy at both hospitals. 220 patients received a fixed dose of 400 MBq over the past 6 years (Group A) and 584 patients received 550 MBq over a 10-year period (Group B). At both centres antithyroid drugs were withdrawn for a week prior to RAI therapy and patients were considered to be cured if they were euthyroid or hypothyroid. Second dose was administered if the patient remained hyperthyroid at 6 months.
Results: Both groups were comparable for age, gender distribution, aetiology of hyperthyroidism and FT4 level at diagnosis. Group A had a significantly higher rate of persistent hyperthyroidism at 3 months (19 vs 9%, P<0.01) and at 6 months (13.6 vs 6.5%, P<0.01). The proportion of patients who were hypothyroid at the end of one year was lower in Group A although this was not statistically significant (67.1 vs 69.9%, P=0.2). Mean total RAI activity administered to patients in Group A was significantly lower (463 vs 596 MBq) and post-RAI restrictions were 45 days shorter.
Conclusions: Fixed dose RAI activity of 550 MBq achieves cure of hyperthyroidism early and in a higher proportion of patients. These improved outcomes are achieved at the expense of a higher mean RAI dose, an extended period of post-RAI restrictions and possibly higher early hypothyroidism rate.