Thyroid Research Thyroid Research Archive Hyperthyroidism

Fixed doses of radioactive iodine are as effective as thyroid activity- and size-adjusted doses for hyperthyroidism

(July 2003)

The background of the study. Patients with hyperthyroidism caused by Graves' disease are often treated with radioactive iodine-131 (I-131). There is no standard method for estimating dosage. In this study, four methods of dose estimation were evaluated.

How the study was done. The study subjects were 88 patients (mean age, 41 years) with hyperthyroidism caused by Graves' disease. After measurements of I-131 uptake and thyroid size, the patients were randomly assigned to receive a therapeutic dose of I-131 calculated in one of four ways; low fixed dose, 6.4 mCi; high fixed dose, 9.4 mCi; low adjusted dose, 80 µCi/g; and high adjusted dose, 120 µCi (the adjustment was for 24-hour I-131 uptake and thyroid weight). After treatment, the patients were evaluated periodically by the referring physician; neither the patient nor the physician knew of the treatment-group assignment. The outcomes were persistent or recurrent hyperthyroidism, hypothyroidism, and normal thyroid function at the end of the follow-up period.

The results of the study. The characteristics of the patients in the four groups at the time of diagnosis of hyperthyroidism and of I-131 treatment were similar. During an average follow-up period of 80 months, 21 patients (24 percent) had persistent or recurrent hyperthyroidism, 61 (69 percent) had hypothyroidism, and only 6 (7 percent) were euthyroid. There were no differences in outcome in the four treatment groups. The mean doses of I-131 administered to the patients in the three outcome groups were similar. The times to recurrent or persistent hyperthyroidism or hypothyroidism were also similar; in most patients the outcome was reached four to six months after treatment.

The conclusions of the study. Fixed doses of I-131 are as effective as doses calculated on the basis of thyroid activity and size for treatment of hyperthyroidism caused by Graves' disease.

The original article. Leslie WD, Ward L, Salamon EA, Ludwig S, Rowe RC, Cowden EA. A randomized comparison of radioiodine doses in Graves' hyperthyroidism. J Clin Endocrinol Metab 2003;88:978-83.