Effect of LET and track structure on the statistical distribution of chromosome aberrations Original Research Article

Chromosome aberration data obtained for various types of mammalian cells after exposure to low and high LET radiation clearly demonstrate differences in the energy deposition pattern of both radiation qualities. In the present study we focus on the distributions of chromosome aberrations induced in human peripheral blood lymphocytes after exposure to 990 MeV/u Fe ions (LET = 155 keV/μm) or X-rays. For the analysis three different types of distributions were applied, namely a Poisson distribution, a compound Poisson–Poisson (Neyman type A) distribution and a convoluted Poisson–Neyman distribution. The analysis showed that after low LET radiation the distribution of aberrations can be well described by Poisson statistics, reflecting a simple random distribution of damages as expected according to the homogeneous pattern of energy depositions. In contrast, for particles the energy is deposited spatially very inhomogeneous and concentrated along the ion trajectories. After exposure to high energy, high LET particles where the track radius is much larger than the cell nucleus, best fits to the data were achieved by a convoluted Poisson–Neyman statistics. The analysis indicates that, under this exposure condition, the distribution of aberrations is determined by two independent components. The first component is determined by the damage induced by a center of the tracks and follows the Neyman distribution. The second component is determined by the overlapping part of tracks which in the case of very high energetic particles leads to a “photon-like” background dose and is thus characterized by a Poisson distribution.