Endocrine Abstracts

Background: Radioiodine ablation is an effective curative treatment for hyperthyroidism in virtually all patients with single or multiple doses. The dosage of radioiodine used in the treatment of thyrotoxicosis has varied widely according to local experience and practice. Administration of low doses could lead to inadequate or delayed response, while using larger doses is associated with the risk of increased incidence of hypothyroidism.

Introduction: In our centre, until mid-2004, clinical attempts were made to titrate the dose of radioiodine administered, based on goitre size, disease activity and underlying diagnosis. Patients received between 220 and 660 MBq. However, in light of absence of evidence that precision dosimetry improves outcome, routine practice was revised to give all patients a fixed dose of 400 MBq.

Methods: All patients who received radioiodine had thyroid function tests at 6 weeks, 3 months, 6 months and 12 months following radioiodine. Patients were classified as euthyroid (fT4 normal, TSH normal), hypothyroid (fT4 low and TSH raised) or hyperthyroid (fT4 raised, TSH low) based on their thyroid function tests.

Results: Of a total of 103 patients, 47 received a calculated dose while 56 received fixed dose. At 1 year of follow up, 22 (46.8%) of those who received a calculated dose were euthyroid compared to 19 (33.9%) who received fixed dose. About 20 (42.6%) in the calculated dose cohort were hypothyroid at one year compared to 33 (58.9%) in the fixed dose group. About 2 (4.2%) in the calculated-dose group remained thyrotoxic at one year compared to 3 (5.4%) in the fixed dose group. Follow-up data was unavailable for 3 (6.4%) patients in the calculated dose group and 1 (1.8%) in the fixed dose cohort.

Conclusions: Fixed and calculated doses of radioiodine in our cohorts achieved similar cure rate for hyperthyroidism.