No abstract

A new physical module for the biophysical simulation code PARTRAC has recently been developed, based on newly derived electron inelastic-scattering cross-sections in liquid water. In the present work, two modules of PARTRAC describing the production, diffusion and interaction of chemical species were developed with the specific purpose of quantifying the role of the uncertainties in the parameters controlling the early stages of liquid water radiolysis. A set of values for such parameters was identified, and time-dependent yields and frequency distributions of chemical species produced by electrons of different energies were calculated. The calculated yields were in good agreement with available data and simulations, thus confirming the reliability of the code. As the primary-electron energy decreases down to 1 keV, the *OH decay kinetics were found to get faster, reflecting variations in the spatial distribution of the initial energy depositions. In agreement with analogous works, an opposite trend was found for energies of a few hundred eV, due to the very small number of species involved. The spreading effects shown at long times by *OH frequency distributions following 1 keV irradiation were found to be essentially due to stochastic aspects of the chemical stage, whereas for 1 MeV tracks the physical and pre-chemical stages also were found to play a significant role. Relevant differences in the calculated e(aq) -yields were found by coupling the physics of PARTRAC with descriptions of the pre-chemical and chemical stages adopted in different models. This indicates a strict interrelation of the various stages, and thus a strong dependence of the parameter values on the assumptions made for the preceding and subsequent stages of the process. Although equally acceptable results can be obtained starting from different assumptions, it is necessary to keep control of such uncertainties, since they can significantly influence the modeling of radical attack on DNA and, more generally, radiobiological damage estimation. This study confirms the need for new, independently derived data on specific steps of water radiolysis, to be included in comprehensive biophysical simulation codes.

No abstract

Knowledge of radiation track structure and its interaction with biological targets is a fundamental starting point in understanding the mechanisms underlying the induction of biological damage. In this context Monte Carlo codes are a powerful tool of investigation, allowing one to simulate both track structure and the features of the target(s) of interest at different scales, from nanometres (linear dimensions of DNA) to micrometres (linear dimensions of human cell nuclei and interphase chromosome territories). In the light of recent experimental findings on nuclear architecture, different approaches in modelling chromosome structure and aberration induction are discussed. In particular, a model is presented in which chromosome territories were explicitly described as subnuclear regions and aberration induction was modelled by coupling the structure of the target with that of the radiation track. Comparisons between model predictions and experimental results from the literature are also reported.