SU-E-T-46: A Monte Carlo Investigation of Radiation Interactions with Gold Nanoparticles in Water for 6 MV, 85 KeV and 40 KeV Photon Beams

Purpose: To determine the effect of gold-nanoparticles (AuNPs) on energy deposition in water for different irradiation conditions. Methods: TOPAS version B12 Monte Carlo code was used to simulate energy deposition in water from monoenergetic 40 keV and 85 keV photon beams and a 6 MV Varian Clinac photon beam (IAEA phase space file, 10x10 cm2, SSD 100 cm). For the 40 and 85 keV beams, monoenergetic 2x2 mm2 parallel beams were used to irradiate a 30x30x10 µm 3 water mini-phantom located at 1.5 cm depth in a 30x30x50 cm3 water phantom. 5000 AuNPs of 50 nm diameter were randomly distributed inside the mini-phantom. Energy deposition was scored in the mini-phantom with the AuNPs’ material set to gold and then water. For the 6 MV beam, we created another phase space (PHSP) file on the surface of a 2 mm diameter sphere located at 1.5 cm depth in the water phantom. The PHSP file consisted of all particles entering the sphere including backscattered particles. Simulations were then performed using the new PHSP as the source with the mini-phantom centered in a 2 mm diameter water sphere in vacuum. The g4em-livermore reference list was used with “EMRangeMin/EMRangeMax = 100 eV/7 MeV” and “SetProductionCutLowerEdge = 990 eV” to create the new PHSP, and “SetProductionCutLowerEdge = 100 eV” for the mini-phantom simulations. All other parameters were set as defaults (“finalRange = 100 µm”). Results: The addition of AuNPs resulted in an increase in the mini-phantom energy deposition of (7.5 ± 8.7)%, (1.6 ± 8.2)%, and (−0.6 ± 1.1)% for 40 keV, 85 keV and 6 MV beams respectively. Conclusion: Enhanced energy deposition was seen at low photon energies, but decreased with increasing energy. No enhancement was observed for the 6 MV beam. Future work is required to decrease the statistical uncertainties in the simulations. This research is partially supported from institutional funds from the Center for Radiation Oncology Research, The University of Texas MD Anderson Cancer Center.