Cataractogenic Effects of Low-LET Radiation More Likely Non-Existent. Report 2. Epidemiological Studies

Radiation disorders to the eye 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-LET radiation doses (up to 100 mGy), the interest in the problem of cataractogenic disorders is growing although there is no clarification of the issue yet. This study consisting of two reports attempts to fill this gap. Report 1 reviewed research into 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 uncertainties associated with epidemiological studies such as the ambiguity of the relationship between lens disorders and the formation of cataracts, their dependence on age, and the dependence of the estimate on the accepted system for classifying opacities. These uncertainties resulted in that since 1977 the ICRP has proposed five successively decreasing threshold doses/limits for lens disorders. The dose regularities for radiogenic disorders of the lens are considered in nine exposed groups mentioned in the reviews including atomic bomb survivors (LSS), Chernobyl liquidators , medical radiologists (roentgenologists, technologists), patients after computed tomography and radiotherapy, industrial radiographers, nuclear workers, residents exposed to an increased background radiation (natural or man-made), and cosmonauts/astronauts and pilots. There were statements about the effects of low radiation doses for some groups , but the presence of some epidemiological uncertainties (reverse causality in diagnostic exposure, the contribution of the exposure of cosmonauts/astronauts and pilots to high-LET radiation, UV, and solar radiation, 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 the ICRP-118, although due to the precautionary principle and based on the data discussed in Reports 1 and 2, the limit can be reduced to 200 mGy. Exceptions are medical radiologists (roentgenologists, technologists) and industrial radiographers for whom the cataractogenic effects of low doses (several tens of milligray; the working minimum being 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 these two groups should limit themselves in future when testing for radiation-induced lens disorders after exposure to low-LET radiation doses while the other groups have no future in this regard.