Purpose: This study investigated the dosimetric change when a gold nanoparticle (GNP) was positioned close to a DNA molecule irradiated by a proton beam. Variations of the dose enhancement due to proton distance between the DNA and GNP, size of the GNP and proton beam energy were predicted using Monte Carlo simulation.
Methods: Monte Carlo simulation was carried out using the Geant4-DNA code for DNA nanodosimetry. The simulation model contained a GNP positioned between a parallel proton beam source and a DNA molecule. The distance between the DNA and the GNP varied between 30 and 130 nm. The size of the GNP varied between 15 and 50 nm and the proton beam energy was in the range of 0.5 – 25 MeV. The field size of proton beam was set to twice the diameter of the GNP. Dose enhancement ratio (DER), defined as the dose at the DNA with GNP to dose at the DNA without GNP, was calculated as per different distances between the DNA and GNP, sizes of the GNP and proton beam energies.
Results: Monte Carlo results on DER showed that the dose enhancement increased with a decrease of distance between the DNA and GNP. Moreover, the DER value also increased with a decrease of proton beam energy. The maximum DER was found 1.83 at the 25 nm radius GNP, irradiated by a 0.5 MeV proton beam and 30 nm away from the DNA. Dependences of DER value on the NP size were found related to the gold mass/volume, secondary electron range and self-absorption of the GNP.
Conclusion: It is concluded that dose enhancement in DNA happened when a GNP was present in a proton beam irradiation. The dose enhancement varied with the distance between the DNA and GNP, size of the GNP and proton beam energy.