Radiotoxicity after iodine-131 therapy for thyroid cancer using the micronucleus assay

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radiation damage to lymphocytes after I- 131 therapy using the cytokines is-blocked micronucleus as s a y . The chromosomal damage to lymphocytes induced by I-131 in vivo should result in augmentation of the cells with micronuclei. Methods ; We studied 25 patients with differentiated thyroid carcinoma, who were treated with 3.7 GBq of I- 131. Isolated lymphocytes collected from patients 1 week after therapy were harvested and treated according to the cytokines is-blocked method of Fenech and Morley. Micronuclens number of micronuclei per 500b inucleated cells was scored by visual inspction. As controls, lymphocytes from the same patients before therapy were also studied. In an in vitro study, lymphocytes from three patients at least 3 months after therapy were exposed doses varying from 0.25 to 1 Gy and stud led with the same method. Results : The mean number (mean*SD) of micronuclei after treatment was significantly increased (p<0.05) as comparted to control subjects (15.7* 2.7 vs. 5.4 * 1.4). Since there was an interval ranging from 6 to 20 months (mean 11.8 months) between the present and the last radio iodine therapy, no significant effect on the frequency of micronucleus with cumulative radiation exposure of I- 131 to lymphocytes was detected. Internal radiation absorbed doses estimated for 25 patients were 0.33 0.09 Gy ln this external irradiation study. C o n c I u s i o n s : The relatively low frequency of lymphocyte micronuclei induced by iodine-13 1 in vivo and lack of significant effect on the frequency of lymphocyte micronuclei with cumulative iodine-131 s u p p o r t e d the contention t h a t short-term non-stochastic damage of this therapy with 3 .7 G B q of 1-131 in thyroid cancer patientsis minimal and reversible .