Gold nanoparticle DNA damage in radiotherapy: A Monte Carlo study

This study investigated the DNA damage due to the dose enhancement of using gold nanoparticles (GNPs) as a radiation sensitizer in radiotherapy. Nanodosimetry of a photon irradiated GNP was performed with Monte Carlo simulations using Geant4-DNA (ver. 10.2) in the nanometer scale. In the simulation model, GNP spheres (with diameters of 30, 50, and 100 nm) and a DNA model were placed in a water cube (1 mu m(3)). The GNPs were irradiated by photon beams with varying energies (50, 100, and 150 keV), which produced secondary electrons, enhancing the dose to the DNA. To investigate the dose enhancement effect at the DNA level, energy deposition to the DNA with and without the GNP were determined in simulations for calculation of the dose enhancement ratio (DER). The distance between the GNP and the DNA molecule was varied to determine its effect on the DER. Monte Carlo results were collected for three variables; GNP size, distances between the GNP and DNA molecule, and the photon beam energy. The DER was found to increase with the size of GNP and decrease with the distance between the GNP and DNA molecule. The largest DER was found to be 3.7 when a GNP (100 nm diameter) was irradiated by a 150 keV photon beam set at 30 nm from the DNA molecule. We conclude that there is significant dependency of the DER on GNP size, distance to the DNA and photon energy and have simulated those relationships.