Two-step radioiodine therapy during a single hospital visit in patients with benign thyroid disorders - Observations on 100 patients

Aim: A two-step radioiodine therapy (RITh) is occasionally necessary in pat ients with benign thyroid disorders, when strong differences to the prether apeutic radioiodine test occur. in this study, the parameters (uptake and e ffective half-life of I-131) of the radioiodine test are compared with thos e of the first and second RITh. Methods: 100 patients were evaluated, who r eceived a two-step RITh in our department between June 1992 and March 1994. Uptake and effective half-life of I-131 and the absorbed dose in the first and second therapy were compared with each other based on the daily measur ed activity of the thyroid. Results: A two-step RITh was necessary in 10% o f the patients. The uptake of I-131 in the first RITh was significantly low er as compared to the test and significantly higher as compared to the seco nd RITh. There were no significant changes between the effective half-life of I-131 in test, first and second RITh. Conclusion: The importance of radi oiodine test for the calculation of therapeutic doses is emphasized. The da ta gathered in our study concerning the diminution of uptake of I-131 in th e second RITh can be useful for dose calculation.