Biophysical Models of Radiation Action - Development of Simulation Codes

Abstract

Radiation carcinogenesis from different radiation fields at low doses and low dose rates remains to be an important research topic in radiation protection. Most likely particular modification of DNA play a decisive role in the initiation steps of carcinogenesis, and, thus, detailed analyses must be performed of the interaction events of different radiation fields with DNA and of their quantitative correlation with the yields of important cellular responses (e.g. transformations). Such analysis must comprise detailed simulations in a computer of all relevant physical interaction processes, the simulation of the subsequent direct chemical modifications of the DNA and the surrounding cellular structures and of those occurring through subsequent diffusion controlled chemical reactions, and a correlation study of the frequency of important events deemed relevant in this context with frequencies of important cellular responses (e.g. DNA strand breaks, chromosome changes, transformations) using mechanistic working hypotheses for the initial carcinogenetic actions of different radiation fields.

This paper describes the state of the art in the simulation of charged particle tracks from various radiation fields (photons, neutrons, internal emitters) in biological cells for the calculation of direct and indirect modifications of the DNA. A significant progress could be achieved through the recent availability of interaction cross sections for condensed molecules and of very powerful parallel computers. Presently the main shortcomings in the track structure approach to understand radiation action are the lack of solid information on the migration and decay of excited states in DNA, and of good working hypotheses for relevant sensitive target structures in a cell and the chemical changes needed in them to trigger initiating steps in radiation carcinogenesis.