Purpose: This Monte Carlo study investigated the dose enhancement of prostate volumetric modulated arc therapy (VMAT) with variations of nanoparticle material, nanoparticle concentration, prostate size, patient size, presence of flattening filter and photon beam energy, when gold nanoparticles (GNPs) were added to the target (prostate).
Methods: A Monte Carlo pelvis phantom was used with variations of prostate (2.5 â€“ 5.5 cm) and phantom (20 â€“ 30 cm) size. Flattening-filter-free (FFF) and flattening-filter (FF) photon beams with energies of 6 and 10 MV, produced by a TrueBEAM Varian linac were used. Monte Carlo simulation (macroscopic approach) was carried out to determine the dose enhancement ratio (DER), which is the ratio of the target dose with GNP addition to the target dose without GNP addition in the simulation.
Results: The highest DER of 1.15 was found when using GNPs with the highest concentration of 40 mg/ml in this study, compared to other nanoparticle materials, namely, platinum, iodine, silver and iron oxide. Moreover, DER was found increasing with a decrease of prostate and phantom size when GNPs were added to the prostate. When comparing the FFF and FF photon beams, the FFF beam had a higher DER. This shows that more low-energy photon in the FFF beam compared to the FF would benefit the dose enhancement as GNPs were added to the target. This agreed with the DER of the 6 MV photon beam being higher than that of the 10 MV, because there were more low-energy photons in the 6 MV beam.
Conclusion: From the Monte Carlo results, it is concluded that when GNPs were added to the prostate in VMAT, dose enhancement was increased with an increase of nanoparticle concentration, decrease of prostate and patient size, the use of the FFF and lower energy of the photon beam (6 MV).