Cataractogenic Effects щf Low-Dose Radiation цith Low Let: More not Than There. Report 2. Epidemiological Studies

Abstract

Radiation damage to the lens is considered to be the third most important effect of radiation, after mortality from cancer and diseases of the circulatory system (ICRP-118). In terms of the effects of low dose radiation with low LET (up to 100 mGy), interest in the problem of cataractogenic disorders is growing, although there is no clarification of the issue. In the present study, two reports attempt to fill this gap. Report 1 reviewed the work on cataractogenic effects of the lowest doses of radiation with low LET in experiments in vitro and in vivo and concluded that there was no significant confirmation of them in animal experiments; Report 2 presents the results of epidemiological studies relevant to the problem. Data are presented on the uncertainties associated with such epidemiological studies: the ambiguity of the relationship between disorders in the lens and the formation of cataracts, their dependence on age, as well as the dependence of the estimation on the accepted system for classifying opacities. These uncertainties have had the consequence that since 1977 the ICRP has proposed five successively decreasing threshold doses (limits) for lens disorders. The dose patterns for radiogenic damage to the lens in the nine exposed groups mentioned in the reviews are considered: victims of atomic bombings (LSS), liquidators of the Chernobyl accident, medical radiologists (rentgenologists, technologists), patients after computed tomography and radiotherapy, industrial radiographers, nuclear industry workers, residents living with an increased radiation background (natural and man-made), for cosmonauts/astronauts and pilots. For some groups, there were statements about the effects of low doses of radiation, however, the presence of a number of epidemiological uncertainties (reverse causality in diagnostic exposure, the contribution of radiation with high LET, UV and solar radiation in cosmonauts/astronauts and pilots, doses above 100 mGy for the upper limit of the studied range in residents, etc.) do not allow us to consider these statements as proven. Therefore, for most exposed groups, a threshold of 300 mGy should be adhered to, regardless of acute or chronic exposure, according to ICRP-118, although due to the precautionary principle, based on the data discussed in Reports 1 and 2, the limit can be reduce to 200 mGy. Exceptions are medical radiologists (rentgenologists, technologists) and industrial radiographers, for whom the cataractogenic effects of low doses (several tens of milligray; working minimum – 20 mGy) can be real. This is probably due to the direct involvement of the organ of vision in professional manipulations with radiation. It is concluded that it is expedient to limit ourselves to these two groups in the future when studying radiogenic disorders in the lens after exposure to low doses of low-LET radiation, while the other groups are unpromising in this regard.