A comparison of physical and cytogenetic estimates of radiation dose in patients treated with iodine-131 for thyroid carcinoma.

Physical and cytogenetic estimates of the whole-body radiation doses have been compared in 11 patients receiving large doses of iodine-131 for the treatment of thyroid carcinoma. The physical estimate was based on the measurement of thyroid uptake, of the plasma activity variation, and of urinary activity. The cytogenetic estimate was obtained from the analysis of chromosome aberrations in peripheral blood lymphocytes. Good agreement between the estimates was observed in patients whose thyroid glands had previously been ablated by radioiodine. In patients who had varying degrees of thyroid function, there were considerable differences between the estimates with the cytogenetic value always being higher. It is suggested that these differences might be due in part to non-uniform irradiation of lymphocytes by local sources of activity in the thyroid and in the liver.     

Equal induction and persistence of chromosome aberrations involving chromosomes 1, 4 and 10 in thyroid cancer patients treated with radioactive iodine

A number of in vitro studies have questioned the assumption of random distribution of breaks in radiation-induced chromosome aberrations. The therapeutic application of radioactive 131I in thyroid cancer patients offers a good opportunity to study the induction and persistence of cytogenetic damage involving different chromosomes in vivo. Using whole-chromosome painting probes and triple colour painting by fluorescence in situ hybridization (FISH), we have analysed the frequency of chromosomal aberrations (CAs) involving chromosomes 1, 4 and 10 in peripheral blood lymphocytes of 10 thyroid cancer patients sampled before and 1 week, 1 year and 3.5 years after therapeutic application of radioactive iodine in a self-controlled, longitudinal study. A highly significant 3.4-fold increase in the frequency of chromosome breaks was observed 1 week after treatment with a similar representation of all chromosomes analysed. Although a significant decrease in dicentrics was observed during the first year after treatment, the frequency of chromosome aberrations remained over control levels until the last sampling time, 41-47 months post-treatment. The same behaviour, in terms of induction and persistence, was observed for all three chromosomes, confirming our previous results in vitro and rejecting the reported suggestion that chromosome 10 is radiosensitive in vivo. Our finding that the dynamics of radiation-induced CA in vivo is independent on the chromosome of choice suggests that this variable is not important in retrospective studies.