Comparison of chromosomal damage induced by X-rays and Ar ions with an LET of 1840 keV/ mum in G1 V79 cells

Abstract

Synchronous V79 Chinese hamster cells were exposed in G1 to either X-rays or 4.6 MeV/u Ar-ions (LET = 1840 keV/micrometer) and the induction of chromosomal damage was measured at five sampling times ranging from 14 to 30 h after treatment. To distinguish between cells in the first and second post-irradiation cycle the fluorescence-plus-Giemsa technique was applied. The experiment showed that the time-course of the appearance of damaged cells was markedly influenced by radiation-induced cell cycle delays and depended on both radiation quality and dose. The yield of aberrant metaphases and the number of aberrations per metaphase was found to increase with sampling time, but this increase was more pronounced for Ar ions. These differences in yield-time profiles of X-ray and Ar ion induced chromosomal damage are particularly important for an accurate determination of the RBE for particles. Our data clearly indicate that meaningful RBEs can only be obtained if chromosomal damage is analysed at several post-irradiation sampling times and the complete time-course of the expression of chromosomal damage is taken into account. Besides these quantitative differences, differences in the spectrum of chromosomal lesions were observed for X-rays and Ar ions. Following particle exposure more breaks and less exchange-type aberrations were formed compared with X-irradiation and, despite irradiation in G(1), a significant number of chromatid-type aberrations occurred in Ar-irradiated samples. The experimental results are interpreted on the basis of the different pattern of energy deposition by sparsely and densely ionizing radiation. In addition, a statistical analysis based on the Neyman type A distribution is performed, which takes into account the specific stochastic properties of particle irradiation.

High yields of isochromatid breaks and successive formation of chromosome exchanges may lead to reproductive cell death following high-LET irradiation

“…The distributions of the chromatid breaks/gaps produced by the irradiation with high-LET irradiation are broader and like a Neyman type A distribution as reported previously [20,58], while those with low-LET irradiations are narrow and show a typical Poisson like distribution. Since charged particles of high-LET produce more ionization/excitation along with these tracks compared with those of low-LET [56], thus the number of incident charged particles of high-LET ions is much smaller than that of low-LET radiation as to give the same absorbed dose in material.…”

“…(c) The distributions of the isochromatid breaks and chromatid breaks produced by irradiation with high-LET heavy ions may be defined by a broader Neyman type A distribution as reported previously [20,58], while those with low-LET ions are narrow, with a Poisson like shape. This may reflect the different physical track structure between high-LET and low-LET irradiation [56,60].…”

“…Small numbers of high-LET particles irradiate the cells in a more heterogeneous fashion than low-LET radiation. Hence, Neyman type A distributions may provide a more suitable explanation for the distribution of high-LET irradiation-produced chromatid breaks/gaps [58].…”

G2 chromatid damage and repair kinetics in normal human fibroblast cells exposed to low- or high-LET radiation

“…Although cytogenetic damage is typically evaluated in the mitotic phase of the cell cycle, this raises problems because many cells experience severe cell cycle delays and interphase cell death (Suzuki et al, 1990;Ritter et al, 1992Ritter et al, , 1996Edwards et al, 1994Edwards et al, , 1996George et al, 2001), especially after high-LET radiation exposure. Assessing damage in interphase chromosomes can reduce some of these problems and produce a more accurate determination of cytogenetic effects following high-LET exposure.…”

Bivariate Poisson–Poisson model of zero-inflated absenteeism data

“…Applications of this univariate distribution to medical data have been scarce and they tended to take place in pre-clinical experiments, e.g. studies of radiation and chromosomal damage [18] and signal and noise detection in the human visual system [19]. Holgate [20] described several bivariate generalizations of the P-P distribution, including the present one.…”