82nd Annual Meeting of the American Thyroid Association:

Which Iodine-131 Dose Is More Efficacious in Graves’ Disease Patients? 5 mCi or 10 mCi?

Patients with Graves’ disease (GD) can be treated with iodine-131 doses, but how to determine the dose is controversial.  There are two fixed doses often used—5 mCi and 10 mCi—and deciding between these is based on a calculation of gland size, iodine uptake, and iodine turnover.

Researchers from India presented at poster at the American Thyroid Association 2012 Annual Meeting of a retrospective analysis comparing 5 mCi and 10 mCi iodine-131 doses used in female patients newly diagnosed with GD.  The poster was “Comparison of Efficacy of Two Fixed Doses of 131I Radioiodine Therapy (5 vs. 10 mCi) in Female Patients with Graves’ Disease.”

In the study, there were 227 patients (mean age: 38 ± 10.8 years).  They were all treated with iodine-131 therapy at initial GD diagnosis between 1998 and 2006.  There were 77 women who received the 5 mCi dose; 150 received the 10 mCi dose.  At baseline, the total T4 was higher in the 10 mCi group (p < 0.01), but in all other aspects, the groups were comparable.

After treatment, all patients were followed for at least 12 months.  To compare the baseline parameters and the difference in outcomes between the groups, student’s t-test and Chi-squared tests were used.  Logistic regression was used for predictors of remission.

Comparison of 5 mCi to 10 mCi Iodine-131 Doses
Overall, the success rate of a single iodine-131 dose was 92.5%.  It was 90.9% in the 5 mCi group and 93.2% in the 10 mCi group.

By one year after treatment, the patients in the 5 mCi group were:

  • 81.8% hypothyroid
  • 9.1% euthyroid
  • 9.1% relapsed

In the 10 mCi group, the rates were:

  • 78.6% hypothyroid
  • 14.6% euthyroid
  • 6.8% relapsed

The Chi-squared tests showed no difference in outcomes between the two groups.

Logistic regression showed that age, weight, height, baseline T4, and TPO positivity were not predictors of successful treatment.

Iodine-131 Doses of 5 mCi Should Be Used in Graves’ Disease Patients
This analysis showed that 10 mCI was no more effective than 5 mCi in treating female patients with Graves’ disease.  The researchers conclude, “[A] routine use of 10 mCi in a fixed-dose approach is not warranted in GD.”

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