Target dose enhancement factor alterations related to interaction between the photon beam energy and gold nanoparticle's size in external radiotherapy: using Monte Carlo method

To study the effects of various sizes of gold nanoparticles (GNPs) on the target tissue dose enhancement factor at the time of external radiotherapy with various photon beam energies ranged from kilovolts (kVs) to Megavolts (MVs) by using Monte Carlo (MC) method. MCNPX code was used for simulating the interaction of photon beams with various levels of energy with water solution including various sizes of GNPs at a presumptive region including a tumor. Initially, a water phantom including GNPs, which consisted a tumor with a size of 1×1×1 cm3 was simulated. The phantom was irradiated with various external monoenergetic photon beam ranged from kVs to MVs. The macroscopic dose enhancement factor (DEF) of the tumor due to the presence of various sizes of GNPs (15, 50, and 100 nm) at a concentration of 7 mg/g was calculated. The tumor (target) DEF at the presence of the GNPs was obtained within the range of 1.69 to 2.66 kV and 1.08 to 1.10 MV photon beam. The highest DEF was found at 50 kV photon beam. The target DEF was increased with the increase in GNPs size. The calculated target DEFs at the presence of GNPs for photon beam energies in kV were similar to the previous studies. For the photon beam energies in MV, after a decrease at the interface of two regions of pure water and solution including the GNPs, DEF the tumor was increased and with 2 and 6 MV energies reached to its maximum at the depths 6.2 and 6.5 cm, respectively.