The In Silico Study of the Influence of the GNPs’ Shapes and Concentrations on the Enhancement of the Dose Within the Bragg Peak in Proton Therapy

In this work, we applied Monte Carlo simulations (GATE/GEANT4) to examine the dose enhancement effect of gold nanoparticles (GNPs) for the proton energies used in clinical radiotherapy (60, 120, and 180). The gold mass concentrations were from 0.5 to 29.5 mg/cm³for the nanoparticles completely filled with gold atoms and from 0.01 to 0.39 mg/cm³for spherical nanostructures with a single atomic layer. The region within the Bragg peak was considered of interest for therapeutic benefits. The influence of the concentrations and the shapes of the GNPs on a local dose increase in the biological environment represented by the water was studied and a relatively small dose increase was observed. The dose enhancement factor (DEF) was found to increase with the gold concentration, being the highest for the target volume when the nanoparticles were fully filled by gold atoms. The maximum increases in DEF did not exceed tenths of a percent, except for nanospheres and nanocubes, where at the maximum considered concentrations of GNPs (29.5 mg/cm³) they reached about 1.3% for the GEANT4-DNA models and even exceeded 1.5% for the Livermore models. Furthermore, in order to explain the dose increase mechanism we compared the model of a spherical nanoparticle filled with gold atoms with a spherical nanoparticle made of a single atomic layer. This study confirms the potential of Monte Carlo simulations of the radiosensitization/radioenhancement processes in proton therapy that uses GNPs. Further studies of the basic mechanisms responsible for the radiosensitization effect of GNPs in therapeutic proton energy ranges are necessary.