SU‐E‐T‐18: Nanoscale Proton Dose Distributions Using GEANT4‐DNA Simulation

Abstract

Purpose: To simulate the energy deposition patterns of 1 MeV proton beam in three different nanoscale size spherical water targets. Methods: In this study, GEANT4 version 9.4 with the DNA physics package demonstrated in one of the advanced examples “microdosimetry” was used. In order to mimic typical cell geometry, three spherical targets of water with diameters of 200, 20 and 2 nanometer were placed in a cube of water (10 × 10 × 10 micrometer3). The interactions listed in the DNA package were applied to these three spherical targets where secondary electrons were tracked down to 5 eV. The standard electromagnetic interaction processes were used in the volume of the cube outside the spherical targets. Proton beams of 1 MeV were used to travel through the spherical targets. One thousand incident proton histories per spherical target were studied in the simulations. The frequency distributions of energy deposited (eV) per nanometer in the Results: With the decrease of the of the target dimensions, the shapes of the frequency distribution of the energy depositions per nanometer in the spherical targets were observed to gradually become asymmetric. The mean energy depositions were found to be 29, 24.5 and 14.8 eV/nanometer for 200, 20 and 2 nanometer diameter targets, respectively. Conclusions: The energy deposition patterns at the DNA environment directly affect sub‐cellular radiation damage and lesion repair mechanism and thus are essential for biophysics models to estimate the radiobiological effects. The trend of increasing asymmetry showed in this study in dose distributions for smaller nanoscale target demonstrate the usefulness of GEANT4‐DNA package as a powerful tool to better understand the physical basis of dose deposition in realistic size of DNA to accurately predict the cellular radiobiological effect due to particle irradiation.