Studying low dose effects using single particle microbeam irradiation

Our current understanding of the effects of low doses of ionising radiation relies on extrapolation from doses which are orders of magnitude larger than those resulting from environmental or occupational exposure. This has been necessary, in part, because the stochastic nature of energy deposition by charged particle tracks makes it difficult to measure effects at low doses. At low doses test populations consist primarily of unirradiated cells, with a few cells which have been traversed by one track and a very small fraction which have been traversed by two or more tracks. Furthermore, the position of tracks relative to critical structures in the cells are random, resulting in large variations in the probability of an effect from one irradiated cell to another. These limitations on the study of the relationship between energy deposited in the cell and the biological effect can be largely eliminated by irradiating individual cells with a counted number of monoenergetic charged particles collimated so that they traverse specific target structures. (author)