New Geant4-DNA physics model for electron track-structure simulations in gold nanoparticles

<i>Objective.</i>To develop a new Geant4-DNA physics model for electron track-structure simulations in gold nanoparticles (AuNPs) that overcomes important deficiencies of the current default model and is applicable over a broad energy range from 10 eV to 1 MeV.<i>Approach.</i>A model of the energy-loss-function of solid-Au with parameters optimized by optical data and self-consistency tests is presented and used to calculate inelastic cross sections using the relativistic plane wave Born approximation (RPWBA). Low-energy corrections for non-Born effects are included and a practical approximation to the Landau damping mechanism of plasmon decay is proposed that accounts for secondary electron production and facilitates its application to Monte Carlo (MC) track-structure simulations.<i>Main results.</i>Calculations of inelastic cross sections and stopping power (SP) values for the individual ionization and excitation channels of solid-Au are presented and compared against the current default model of Geant4-DNA (DNA_AU_2016), the Livermore and Penelope low-energy models of Geant4, and other published models. It is shown that the present model improves the current default model of Geant4-DNA by offering almost excellent agreement (∼2% on average) with NIST's SP data (previously at ∼6%), while eliminating the unphysical low-energy overestimation (up to 1000% or more), thus, bringing much better agreement with more elaborate physics models for solid-Au.<i>Significance.</i>MC track-structure codes are considered the gold standard for dose enhancement calculations in AuNP-aided radiotherapy. In particular, the Geant4-DNA toolkit offers functionalities for simulating critical cellular radiobiological effects following AuNP irradiation. Yet the accuracy of such simulations is limited by the quality of the cross sections for the individual electron-AuNP interactions. It is envisioned that the present model will allow Geant4-DNA users to perform more accurate simulations of electron transport within AuNPs and better quantify the outgoing secondary electron spectrum which is responsible for the dose enhancement effect and subsequent radiobiological damage.