Radiotherapy for cancer tumour treatment is reliant on the interactions of secondary species (electrons, positrons, radicals, molecular fragments) with important biomolecules within cells to cause (ideally) apoptosis of cancer cells[1]. In order to control the effects of radiotherapy, both to minimise damage to healthy tissue and increase site specific damage to tumours, a detailed understanding of the physicochemical processes occurring between the biological system and the primary and secondary particles is necessary[3]. Charged particle track simulations for the interaction of secondary electrons with biomolecules are usually performed using water as the medium. This is an oversimplification of the living cell, which is composed of approx. 70% water, 24% macromolecules (proteins, nucleic acids, polysaccharides) and 4% inorganic ions, sugars, amino acids, nucleotides, fatty acids and other small molecules[2]. This work compares the track simulations of a 10keV primary ionizing particle in the water medium with the same in pyrimidine (C4H4N2), the commonly used prototypical structure for RNA/DNA bases. As expected, the results for the two mediums differ, including in the secondary electron penetration depth, indicating that a shift towards mixed media modeling is appropriate to truly determine the physicochemical effects and biological implications of radiation treatment. The simulations used the Low-Energy particle Track Simulations code LEPTS[4], a Monte Carlo code for event by event simulation to describe the underlying mechanisms of electron and positron interactions with the relevant target molecules. This includes not only the energy deposition and the stopping power, but also the number and types of interactions taking place along the particle track. Also presented is a database for the scattering cross sections and stopping power of electrons with Pyrimidine, with recommended values chosen from experiment and calculation to cover the incident electron energy range from 1 - 10000 eV. The data for water has been previously compiled.

POSMOL 2015, 17-20 July 2015, Lisboa, Portugal; http://eventos.fct.unl.pt/posmol2015/

Peer Reviewed