Development and Validation of Proton Track Structure Model Applicable to Arbitrary Materials

Abstract

A novel transport algorithm performing proton track-structure calculations in arbitrary materials was developed. Unlike conventional algorithms, which are based on the dielectric function of the target material, our algorithm uses a total stopping power formula and single-differential cross sections of secondary electron production. The former was used to simulate energy dissipation of incident protons and the latter was used to consider secondary electron production. In this algorithm, the incident proton was transmitted freely in matter until the proton produced a secondary electron. The corresponding ionising energy loss was calculated as the sum of the ionisation energy and the kinetic energy of the secondary electron whereas the non-ionising energy loss was obtained by subtracting the ionising energy loss from the total stopping power. The most remarkable attribute of this model is its applicability to arbitrary materials, i.e. the model utilises the total stopping power and the single-differential cross sections for secondary electron production rather than the material-specific dielectric functions. Benchmarking of the stopping range, radial dose distribution, secondary electron energy spectra in liquid water, and lineal energy in tissue-equivalent gas, against the experimental data taken from literature agreed well. This indicated the accuracy of the present model even for materials other than liquid water. Regarding microscopic energy deposition, this model will be a robust tool for analysing the irradiation effects of cells, semiconductors and detectors.

Improvement of the hybrid approach between Monte Carlo simulation and analytical function for calculating microdosimetric probability densities in macroscopic matter

“…In this study, we adopted the Ion Track Structure model for Arbitrary Radiation and Targets (ITSART) (Ogawa et al 2021) and the Electron Track-Structure mode (ETS-PHITS) (Kai et al 2015a, 2015b, Matsuya et al 2019 implemented in PHITS version 3.31 for analysing the ion and electron trajectories, respectively, in water. It should be mentioned that PHITS works with another track-structure algorithm for ions based on KURBUC-PHITS (Liamsuwan and Nikjoo 2013), but it was not employed in this study because it is applicable to only protons and carbon ions up to 300 MeV and 10 MeV n −1 , respectively.…”

“…The Particle and Heavy Ion Transport code System, PHITS (Sato et al 2018a), is a Monte Carlo code that can analyze the radiation kinetics in both microscopic and macroscopic scales using track-structure algorithms (Matsuya et al 2021, Ogawa et al 2021, Hirata et al 2022a, Matsuya et al 2022b and condensed-history methods (Hirayama et al 2005, Geissel et al 2022, respectively. Furthermore, PHITS has a unique function to instantaneously convert the macroscopic deposition energies calculated using the condensed-history methods to microdosimetric PDs in water using an analytical function developed based on track-structure simulations (Sato et al 2006).…”