Tumor dose enhancement by gold nanoparticles in a 6 MV photon beam: a Monte Carlo study on the size effect of nanoparticles

In this study after benchmarking of Monte Carlo (MC) simulation of a 6 MV linac, the simulation model was used for estimation of tumor dose enhancement by gold nanoparticles (GNPs). The 6 MV photon mode of a Siemens Primus linac was simulated and a percent depth dose and dose profiles values obtained from the simulations were compared with the corresponding measured values. Dose enhancement for various sizes and concentrations of GNPs were studied for two cases with and without the presence of a flattening filter in the beam's path. Tumor dose enhancement with and without the presence of the flattening filter was, respectively 1-5 and 3-10%. The maximum dose enhancement was observed when 200 nm GNPs was used and the concentration was 36 mg/g tumor. Furthermore, larger GNPs resulted in higher dose values in the tumor. After careful observation of the dose enhancement factor data, it was found that there is a poor relation between the nanoparticle size and dose enhancement. It seems that for high energy photons, the dose enhancement is more affected by the concentration of nanoparticles than their size.