Calculation of lineal energies for water and DNA bases using the Rudd model cross sections integrated within the Geant4-DNA processes

Abstract

This study presents new parameters for proton ionisation cross sections in guanine, adenine, thymine, and cytosine based upon the semi-empirical Rudd model. The same model was used to find differential electron cross sections considering a speed scaling procedure. To accelerate computation, the total electron cross sections were obtained using the binary-encounter-Bethe approximation instead of the integrated Rudd formula. The cross sections were implemented in the Geant4 simulation toolkit as Geant4-DNA processes, and simulations were carried out measuring protons lineal energies in spherical micrometric volumes filled with water, adenine, thymine, guanine, and cytosine. Large differences were seen in the lineal energies evaluated for the different materials, with the lineal energy measured in guanine being sometimes twice that of water. This suggests that the cross sections developed here should be considered in biological simulations where cellular substructures are modelled, in contrast to the current approach which approximates these volumes as consisting of liquid water.