Results of 131I-therapy for hyperthyroidism

From 1965 through 1976, 643 patients (134 male and 501 female) who had been treated with 131I for hyperthyroidism were contacted for follow up study. The mean length of follow up study was 5 years. The average dose of 131I was 4.2 mCi (6,000 rad) in early 8 years and 3.6 mCi (5,200 rad) in later 4 years. The incidence of hypothyroidism was 3.9% after one year, 3.8% after two years, 6.4% after three years, 5.0% after four years, 5.3% after five years. 131I therapy, thus, results in an increasing incidence of hypothyroidism with passage of time. One female had been observed thyroid cancer after 5 years from 131I administration. But no deaths and no evidence of leukemia were observed. (author)