Radioiodine therapy of Graves' disease - a dosimetric comparison of different strategies concerning antithyroid drugs

Aim: Premedication with antithyroid drugs (ATD) compared to patients not pr etreated with ATD causes a higher failure rate of radioiodine therapy (RITh ) or demands higher therapeutical dosage of radioiodine (RI). For clinical reasons and because of accelerated iodine metabolism in hyperthyreosis a co mpensated thyroid metabolism is desirable. Aim of this study was to investi gate the influence of ATD on the biokinetics of RI in case of Graves' disea se in order to improve RITh of patients pre-treated with ATD. Methods: 385 consecutive patients who underwent RITh because of Graves' disease for the first time were included: Group A (n = 74): RITh under continuous medicatio n with ATD; Group B (n = 111): Application of RI under continuous medicatio n with ATD, in case of insufficient RI-uptake or shortened effective RI-hal f-life ATD were stopped 1-5 days after RITh; Group C (n = 200): ATD were st opped 2 days prior to RITh in all patients. We examined the influence of AT D on RI-uptake and effective RI-half-life as well as the absorbed dose achi eved on the thyroid in dependence of thyroid volume and applied RI-dosage [ TEQ-therapy efficiency quotient, (2)]. Results: In the RI-pretest (all pati ents under ATD) the RI-uptake was comparable in all three groups. During RI Th RI-uptake, effective RI-half-life and therefore the TEQ were significant ly higher in Group C as compared to Groups A and B (p <0,001, respectively) . In Group B the medication with ATD was stopped in 61 of 111 cases 1-5 day s after RITh. In this subgroup the effective RI-half-life increased from 4, 4 +/- 1,7 d to 5,1 +/- 1,6 d after stopping of ATD (p = 0,001). Conclusion: Stopping of ATD 2 days prior to RITh leads to an increased efficiency of a bout 50% compared to RITh carried out under ATD and therefore to a clear re duction of radiation exposure to the rest of the body with equal absorbed d oses of the thyroid. Stopping of ATD shortly after RITh increases efficienc y in case of short effective RI-half-life, but it is inferior to stopping A TD 2 days prior to RITh.