Time-course of aberrations and their distribution: impact of LET and track structure

Abstract

The biological response to high linear energy transfer (LET) radiation differs considerably from that to low LET radiation and this has been attributed to differences in the spatial energy deposition of both radiation qualities. In the case of X-rays the energy is deposited uniformly within the cell nucleus and produces damages in a purely stochastic manner. In contrast, for particles the energy is deposited inhomogeneously along the ion trajectory and the local dose decays with the square radial distance from the center of the track. This nonuniformity affects the yield and the distribution of aberrations among cells. Moreover, after high LET exposure a relationship between the aberration yield and cell cycle delay was observed. In this study, we present a detailed analysis of the distribution of aberrations in human lymphocytes reaching mitosis at early and later times after low and high LET exposure. Aberration data were fit to stochastic distributions demonstrating that the delay is related to the number of particle traversals per cell nucleus. To further elucidate this relationship, we introduce a Monte Carlo phenomenological model which incorporates the number of particle hits per nucleus. This value was derived by fitting theoretical distributions to the experimental data. Additionally, the probability that a cell traversed by a particle reaches mitosis at a given time was calculated. The analysis of biological data and numerical simulations clearly show the impact of the track structure on the formation of chromosome aberrations and their distribution among cells.