The simulation of dose variation effects due to the presence of different metal nanoparticles under proton irradiation using Geant4 toolkit

The impacts of nanoparticles in radiation therapy have been investigated during the recent decades. The present study was conducted with the aim of investigating the effect of different physical interaction models on dose calculations using gold, hafnium and gadolinium nanoparticles. A nanoparticle with a diameter of 50 nm was simulated in a cubic water phantom and irradiated by protons with the energies of 5, 50 and 150 MeV using Geant4 Monte Carlo toolkit. The current study has considered various parameters, including the energy spectrum of secondary electrons and photons, radial dose distribution (RDD), dose enhancement factor (DEF), around the nanoparticle with three different materials and two physical interaction models. The obtained data showed that for gold nanoparticles, the Penelope model generated a greater number of secondary electrons than the Livermore model; however, for the other two nanoparticles, the Livermore model produced a greater number of secondary electrons than the Penelope model. In the RDD graphs, the Penelope model presents a 10% difference compared to the Livermore model up to a distance of 6 nm from the nanoparticle’s surface (along the radial axis in water). Furthermore, the Livermore model indicates a 16% and 10% increase in dose compared to the Penelope model up to a distance of 9 nm from the surface of hafnium and gadolinium nanoparticles, respectively. In the case of DEF, the dose deposited around the gold nanoparticle was increased by 14, the highest amount compared to DEF of hafnium and gadolinium nanoparticles which is 10 and 6, respectively