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From cell to organism: the need for multiparametric assessment of exposure and biological effects

Radiation Toxicology, Washington State University, TriCities, 2710 University Drive, Richland, WA 99352, USA

Radiation exposure produces a range of responses at every level of biological organisation. As new molecular, cellular, tissue, organ and organism responses are identified, it is essential to relate these responses to exposure parameters. This paper examines the use of different exposure parameters such as dose, fluence, local energy deposition, total energy deposited and hit number, and then relates them to biological responses at different levels of biological organisation. For many responses to high doses of radiation, the dose or energy concentration is the most appropriate and widely used parameter. The best predictor of response for cellular and molecular alterations following exposure to low radiation doses and for non-uniform radiation exposures appears to be "hit" number or the total energy deposited in the biological structure of interest. In many cases, this structure is the cell or the nucleus. To evaluate the probability of producing a cancer in an organ or tissue, the most appropriate measure of physical exposure is radiation dose. Estimation of population risks requires data on the distribution of exposures across that population, an estimate of the excess cancers in the population and a way to relate the exposure to response. The use of total energy in the system as one potential metric to establish this relationship is discussed. This paper provides an overview of the different exposure parameters that can be related to various biological responses, with examples of how these can be related at different levels of biological organisation.