[Radioiodine therapy of Graves' disease--a dosimetric comparison of various therapy regimens of antithyroid agents].
OBJECTIVE
Premedication with antithyroid drugs (ATD) compared to patients not pretreated 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 compensated thyroid metabolism is desirable. Aim of this study was to investigate the influence of ATD on the biokinetics of RI in case of Graves' disease 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 medication with ATD; Group B (n = 111): Application of RI under continuous medication with ATD, in case of insufficient RI-uptake or shortened effective RI-half-life ATD were stopped 1-5 days after RITh; Group C (n = 200): ATD were stopped 2 days prior to RITh in all patients. We examined the influence of ATD on RI-uptake and effective RI-half-life as well as the absorbed dose achieved on the thyroid in dependence of thyroid volume and applied RI-dosage [TEQ--therapy efficiency quotient, (2)].


RESULTS
In the RI-pretest (all patients under ATD) the RI-uptake was comparable in all three groups. During RITh RI-uptake, effective RI-half-life and therefore the TEQ were significantly 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 days 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).


CONCLUSIONS
Stopping of ATD 2 days prior to RITh leads to an increased efficiency of about 50% compared to RITh carried out under ATD and therefore to a clear reduction of radiation exposure to the rest of the body with equal absorbed doses of the thyroid. Stopping of ATD shortly after RITh increases efficiency in case of short effective RI-half-life, but it is inferior to stopping ATD 2 days prior to RITh.
Urbannek
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V
Klinik und Poliklinik für Nuklearmedizin, Medizinische Einrichtungen der Universität zu Köln, Deutschland.
Voth
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E
Moka
D
D
Schicha
H
H
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D013956:Antithyroid Agents / Q000493:pharmacokinetics* / Q000627:therapeutic use*; D003131:Combined Modality Therapy; D005260:Female; D006111:Graves Disease / Q000188:drug therapy* / Q000532:radiotherapy*; D006801:Humans; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D011879:Radiotherapy Dosage; D012189:Retrospective Studies; D016896:Treatment Outcome
D013956:Antithyroid Agents; D007457:Iodine Radioisotopes