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.
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