Low-energy electron dose-point kernels and radial dose distributions around gold nanoparticles: Comparison between MCNP6.1, PENELOPE2014 and Geant4-DNA

With emerging interests in subcellular and nano-scale energy deposition of low-energy electrons, new cross-sectional models for the low-energy electron transport have been integrated into recent releases of Monte Carlo (MC) codes. MCNP6.1 has been released which included extended cross-sections for low-energy electron interactions based on the Evaluated Electron Data Library (EEDL). Moreover, a single-event electron transport method was introduced down to 10 eV. In this study, MCNP6.1 has been benchmarked against early versions of PENELOPE2014 and Geant4-DNA by comparing dose-point kernels (DPKs) of electrons of 100 eV, 1 keV and 10 keV. In addition, radial dose distributions around a 2 or 15 nm-diameter gold nanoparticle (GNP) irradiated by 50 kVp X-rays were calculated for comparison. For all electron energies, the DPKs calculated by MCNP6.1 reached the maximum values at shorter distances and then were decreased more rapidly than those calculated by the other codes. Radial doses within 2 nm from the surface of the GNPs calculated by MCNP6.1 were 1.04 - 1.89 times and 1.13 - 1.58 times higher than those calculated by Geant4-DNA and PENELOPE2014, respectively. These differences would stem from the fact that inelastic cross-sections of MCNP6.1 for low-energy electrons are higher than those of the other codes. At this moment, it is difficult to judge which of the codes is more accurate for nano-scale dose calculations than the others. Depending on the geometrical configuration of the electron source (herein GNPs) and the target (e.g., DNA), the difference in the interaction data for low-energy electron transport, especially below 10 keV, would result in significant differences in calculation of radio-biological effects on the target. It can be concluded that one should pay attention to the interaction data as well as the transport parameters used for MC low-energy radiation transport in a nano- and micro-scale.