Chromosome Aberrations and the Theory of RBE

Summary

Production of chromatid-type aberrations in the generative nucleus of mature pollen of Tradescantia bracteata by monochromatic soft x-rays and hard x- and gamma-rays, and the modifying effect of oxygen has been investigated. Even the lowest energy x-rays, formerly thought to be ineffective, produced aberrations. The effectiveness of a short electron track in producing an aberration depends on its track-length as well as its LET, but the modifying effect of oxygen depends only on the LET. The results are consistent with a model of aberration production in which a primary lesion in a chromosome is produced by one energy-loss event (about 60 ev) in a structure of the order of 1 mµ in thickness, and an aberration results from the interaction of two damaged structures in a site with a radius of the order of 0·2 µ. On the basis of this model derived from data at well-defined LET values, the effectiveness of hard x- or gamma-rays can be accounted for by reference to their LET distributions. The effective LET for aberration production depends on the characteristic site-radius for the particular type of aberration in the cells considered.