DO RECORDED DOSES OVERESTIMATE TRUE DOSES RECEIVED BY CHERNOBYL CLEANUP WORKERS - RESULTS OF CYTOGENETIC ANALYSES OF ESTONIAN WORKERS BY FLUORESCENCE IN-SITU HYBRIDIZATION

Studies of workers who were sent to Chernobyl after the 1986 reactor a ccident are being conducted to provide a better understanding of the e ffects of chronic low-dose radiation exposures. A crucial component to these investigations is an accurate assessment of the radiation doses received during the cleanup activities. To provide information on bio logical measurements of dose, fluorescence in situ hybridization (FISH ) with whole-chromosome painting probes has been applied to quantify s table chromosome aberrations (translocations and insertions) among a d efined cohort of 4,833 cleanup workers from Estonia. Cytogenetic analy sis of 48-h lymphocyte cultures from 118 Estonian cleanup workers (10. 3 cGy mean recorded dose; 25 cGy maximum), 29 Estonian population cont rols and 21 American controls was conducted by three laboratories. Mor e than 258,000 painted metaphases were evaluated. Overall, we observed lower translocation frequencies than has been reported in previous st udies using FISH among Chernobyl cleanup workers. In our data, a clear association with increased levels of translocations was seen with inc reasing age at blood drawing. There was no correlation, however, betwe en aberration frequency and recorded measurements of physical dose or any category of potential high-dose and high-dose-rate exposure such a s being sent to Chernobyl in 1986, working on the roof near the damage d nuclear reactor, working in special zones or having multiple tours. In fact, the translocation frequency was lower among the exposed worke rs than the controls, though not significantly so. To estimate the lev el of effect that would have been expected in a population of men havi ng an average dose of similar to 10 cGy, blood from six donors was exp osed to low-LET radiation, and more than 32,000 metaphases were scored to estimate dose-response coefficients for radiation-induced transloc ations in chromosome pairs 1, 2 and 4. Based on these results, we esti mate that had this group of 118 men received an average whole-body dos e of 10-11 cGy, as chronic or acute exposures, an increase in the mean frequency of chromosome translocations of more than 40-65% would have been observed in their lymphocytes compared to findings in nonirradia ted controls. In spite of evaluating more than a quarter of a million metaphases, we were unable to detect any increase in the mean, median or range in chromosome aberrations in lymphocyte cultures from a group of Estonian men who took part in the cleanup of the Chernobyl nuclear power site and those who did not. We conclude that it is likely that recorded doses for these cleanup workers overestimate their average bo ne marrow doses, perhaps substantially. These results are consistent w ith several negative studies of cancer incidence in Chernobyl cleanup workers and, if borne out, suggest that future studies may not be suff iciently powerful to detect increases in leukemia or cancer, much less distinguish differences between the effects of chronic compared to br ief radiation exposures. (C) 1998 by Radiation Research Society.