Room: Exhibit Hall
Purpose: This study investigated the variation of energy deposition at a DNA using different irradiation geometries of kilovoltage photons on a gold nanoparticle (GNP). The nanodosimetry of the irradiated GNP was determined by the Geant4-DNA Monte Carlo code.
Methods: A Monte Carlo model was constructed consisting of a 1 Î¼mÂ³ water-filled cube with GNP spheres (with radii of 15, 25, and 50 nm) positioned at the centroid, a DNA macromolecule (at distances of 30, 80, and 130 nm away from the GNP), and a photon beam source (of 100 and 200 keV energies). The dose enhancement ratio (DER) was calculated by the energy deposition to the DNA with and without the GNP present. The Monte Carlo simulation was performed using irradiation geometries of a linear and radial photon beam. The linear photon beam irradiated the GNP in a single direction. For the radial photon beam, the photon source was set to emit photons directly at the edge of the GNP at each possible radial degree surrounding the GNP.
Results: The DER increased with the GNP size and decreased with the GNP-to-DNA distance in both irradiation geometries. The largest DER obtained was 4.2 using the 200 keV radial photon beam source to irradiate a GNP (50 nm radius) positioned 30 nm away from the DNA macromolecule. In general the DER values for the radial photon beam geometry were larger. This is likely a result of the closer proximity of the beam to the GNP, as a greater number of secondary electrons were able to irradiate the DNA macromolecule due to the lesser penetration depth required.
Conclusion: It is concluded that the DEF at the DNA varied with the irradiation geometry for the GNP, and the radial beam geometry was found better than the linear beam geometry in increasing the DEF.