Comparative Evaluation Of The Two Fixed Dose Methods Of Radioiodine Therapy (5mci And 10 Mci) For The Treatment Of Grave's Disease

Radioiodine therapy is the safest, simplest, least expensive and most effective method for treatment of Grave's disease. Due to difficulties in previous methods for dose determination, fixed dose method of 1-131 is now considered the best practical method for 1-131 therapy in Grave's disease, but there is no consensus on the dose. We compared two routinely recommended fixed doses of 5 and 10 mCi for this purpose. In this clinical trial, 59 patients with Grave's disease referred for radioiodine therapy were randomized into two groups, one group was treated with 5 mCi of 1-131 and the other with 10 mCi. All patients were followed for two years, with 6-month intervals. Totally, among 59 patients treated with 1-131, 20 (33.9%) patients became euthyroid and 19(32.2%) became hypothyroid, while failed therapy (no response or relapse) was noticed in 20 patients (33.9%). In the group treated by 5 mCi (33 patients), 10(30.3%) were euthyroid, 6(18.2%) were hypothyroid (overall cure of ^8.5%), while 17(51.5%) remained hyperthyroid by the end of the follow-up period. From the 26 patients treated with 10 mCi, the euthyroid and hypothyroid states were observed in 10(38.5%) and 13(50%)patients, respectively (overall cure rate of 88.5%), and hyperthyroid state in 3(11.5%). No relationship was noted between the outcome and age, sex, size of the thyroid gland and thyroid uptake, but the relationship between the disease outcome and the amount of administered radioiodine was significant (P<0.003). Although the incidence rate of early hypothyroidism (by the end of 2 years) in the group treated with 5 mCi is less than those treated with 10 mCi, the incidence of failed therapy is higher in the former group. In addition, it is known that long-term hypothyroidism prevalence is not significantly different by using different doses of I-131. On the other hand, if the initial dose is so little to cure, cost and time for perfect treatment, number of office visits and morbidity due to untreated hyperthyroidism are markedly increased. Regarding lower rate of failed therapy with 10 mCi, and as there is no significant difference in late hypothyroidism between low doses and high doses of I-131, we concluded that 10 mci is the optimal fixed dose for treatment of Grave's disease.