Geant4 interaction model comparison for dose deposition from gold nanoparticles under proton irradiation

Gold nanoparticles (GNPs) have shown a potential as a radiosensitizer in radiotherapy. The radiosensitization effect is thought to be linked to the increased dose deposition around the GNP. Monte Carlo simulations have been implemented for the calculation of the dose distributions around the GNPs and have been used for the calculation of the dose enhancement. They have also been imported to radiobiological models to predict biological endpoints. This work assessed the implications of different physical interaction models on the dose distribution and dose enhancement of GNPs surrounded by water under proton irradiation. The Penelope and Livermore physical interaction model implementation of the Geant4 simulation toolkit were compared considering the following parameters: (i) GNP size, (ii) proton energy, and (iii) alternative physics model parameters in the gold or water medium. We found that neither the dose distribution nor the dose enhancement is sensitive to the model selection after the first 100 nm from the GNP surface. Within the first 100 nm the Livermore models calculated a higher dose, attributed to a higher production of low energy secondary electrons inside the GNP.