SU‐E‐T‐668: Comparison of the Physical Characteristics of Secondary Electrons and Dose Enhancement from X‐Ray Irradiation of Gold Nanoparticles Using Monte Carlo Simulation

Abstract

Purpose: To investigate secondary electron production in gold nanoparticle (GNP) aided radiotherapy through Monte Carlo simulations, thereby advance the understanding of dose enhancements and their role in improving cell kill. Methods: Using the Geant4 toolkit, simulations were performed with four polyenergetic sources, namely 50 kVp, 250 kVp, Cobalt‐60, and 6 MV, to irradiate a gold sphere of diameters 2, 50, or 100 nm in water. The energy of the secondary electrons and the frequency and type of physics interaction that created them were tracked. This allowed calculation of the absorbed dose and energy deposition inside and outside of the nanoparticle. Results: The presence of a GNP can enhance the production of electrons by approximately 3 orders of magnitude at kV beam energies. For MV beams, the increase in electron production was approximately 10 folds. Considerable dose enhancement occurred when gold was present, at approximately 1000 folds for kV beams, and between 2 to 7 folds for MV beams. The energy deposited was calculated to compare how many additional electrons were generated and take into account their energies. In the kV beams, the addition of a GNP caused significantly greater deposited energy surrounding the nanoparticle by 2 to 3 orders of magnitude. For the MV beams, the increase was approximately 5 folds. The proportion of energy deposition inside the GNP versus the outside was also analyzed. At greater nanoparticle diameters, a larger portion of the overall deposited energy resided within the nanoparticle. Conclusions: We present simulation results that show the presence of GNPˈs can considerably increase the dose and energy deposition outside the nanoparticle, especially at kV energies. This enhancement is also present for MV beams, although to a lesser degree.