Room: Track 3
Purpose: To investigate the effect of photon incidence angle on the dose distribution around gold nanoparticles (GNPs) present within a cellular geometry model using full-fledge Geant4 Monte Carlo (MC) simulation in comparison with an analytic approach based on the rescaling of nanoscopic electron dose point kernel (DPK).
Methods: A transmission electron microscopy (TEM) image showing a single cell containing internalized GNPs was used for the current investigation. Specifically, a voxelized cellular geometry model was constructed via the TEM image using gray value thresholding and ported to Geant4 as a geometry file. A clinical 6 MV photon spectrum was applied along the x-y plane (parallel to the cellular surface). The energy deposition to the cellular nucleus, due to the secondary electrons emitted from internalized GNPs, was then scored. The simulation was repeated by changing the photon incidence angle along the z-axis (perpendicular to the cellular surface). After MC simulations, virtual electron tracks were generated from each GNP voxel to calculate the energy deposition to the cellular nucleus by rescaling of MC-derived electron DPKs. Pearson’s product-moment correlation coefficient was calculated for the results derived from the DPK rescaling method and MC simulations.
Results: For perpendicular incidence of photons, the DPK-based results showed reasonable agreement (r ~ 0.86) with MC results. For parallel incidence of photons, the agreement became worse (r~0.63). The DPK method took around 1 hour to obtain the results, whereas MC simulations, conducted on a dedicated high performance computing cluster, took more than 10 hours.
Conclusion: Although not perfectly comparable to full-fledged MC simulations in the case of parallel photon incidence, the DPK method can allow for quick and reliable estimation of the intracellular dose enhancement due to internalized GNPs under a typical cell irradiation geometry (i.e., perpendicular photon incidence).
Funding Support, Disclosures, and Conflict of Interest: Supported in part by CPRIT grant RP160497