Mechanisms underlying cellular radiosensitivity and R.B.E.: introductory remarks.

A general outline of the symposium titled "Mechanisms underlying cellular radiosensitivity and R.B.E." will be given in the introduction. The essential topics of molecular radiation biology are described with respect to the damage, repair and mutagenesis caused by high-LET irradiation to cellular DNA. The importance of clustered DNA lesions (locally multiply damaged sites) formed in vivo is discussed. This symposium is devoted to the mechanisms of the biological effects of radiation with high LET, especially with regard to the effects of heavy ions and neutrons which may cause possible risks in space flight, (e.g. carcinogenesis and mutagenesis). Detailed understanding of these risks, however, demands knowledge of the molecular mechanisms involved in the biological effects of high-LET radiations. Thus, it was the organizers' idea to hold a symposium dealing with primary physical and chemical events caused in cellular deoxyribonucleoproteins by densely-ionizing radiations and to relate them to track structures and energy transfer processes. The mechanisms of DNA damage were regarded from different points of view including those considering DNA repair and mutagenesis. Problems associated with cell survival and radiation protection were discussed as well. Our knowledge of the molecular mechanisms of high-LET radiation actions, however, is limited compared to what we know about low-LET radiation effects (e.g. from gamma-rays or X-rays). To emphasize this statement, I would like to summarize briefly the open questions in molecular radiation biology, what we know already about low-LET effects and what is lacking describing the effect of high-LET radiation.