Endocrine Abstracts

Aim: Radioiodine activities for the treatment of Graves’ disease hyperthyroidism are still subject to discussion, as is the use of a fixed approach over a dosimetric one. We aimed to evaluate our success rate using a personalized dosimetric approach: instead of the “(MBq I-131×g gland mass×100)/(percentage uptake at 24 h)” activity calculation, we further adjusted for factors such as gender, age, diagnosis, 2 h and 4 h radioiodine uptake, previous medication, and clinical history.

Materials and methods: We reviewed data from all patients treated with radioiodine therapy (RIT) for hyperthyroidism at our department (n=179), from January 2008 to January 2016, selected those with Graves’ disease (n=118), and excluded the ones without follow-up (n=11). RIT was considered successful if either euthyroidism or hypothyroidism were achieved. We evaluated success rates differences between lower and higher activities. All statistical analyses were carried out using IBM SPSS version 21.0 for Mac. A type I error 0.05 was considered.

Results: 107 patients were included (44.346±13.07 years; 89 female). RIT was successful in 91.6% (n=98), while 8.4% (n=9) remained hyperthyroid. If we consider the success after the first RIT, 72.0% (n=77) succeeded, while 28.0% (n=30) remained hyperthyroid. 87 (81.3%) were submitted to a single therapy whereas 20 (18.7%) were submitted to multiple RIT. There were no significant outcome differences between the lower and higher activities used (P=0.061).

The used activities ranged between 148 MBq and 703 MBq (335.92±101.60 MBq).

Conclusion: Our results confirm RIT effectiveness in Graves’ disease hyperthyroidism treatment. Although using inferior activities to those generally prescribed (200–800 MBq), we achieved higher success rates – comparable to the best reposted in the literature. There were no statistically significant outcome differences between the lower and higher activities used, highlighting the importance of tailored treatment approaches to warrant the best therapeutic outcome and while avoiding unnecessary exposure.