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Application of the Dose Point Kernel Method for Nanoscale Dose Calculations Around Gold Nanoparticles

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S Jayarathna

S Jayarathna1*, N Manohar2 , M Ahmed1 , S Cho1 , (1) The University of Texas MD Anderson Cancer Center, Houston, Texas, (2) Emory Univ, Atlanta, GA


SU-K-205-3 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: 205

Purpose: To investigate a computational approach, based on the dose point kernel (DPK) method, which may be used for quick estimation of the dose enhancement around gold nanoparticles (GNP) of different geometries due to the secondary electrons produced from GNPs being irradiated by photon sources.

Methods: The spectra of secondary electrons generated within a 250-nm radius GNP were obtained for three commonly used photon sources (250 kVp, Yb-169, and 6 MV) by performing GEANT4 Monte Carlo simulations. The secondary electron spectra were then used for separate GEANT4 simulations to calculate the DPKs in water. Subsequently, the dose distributions around spherical GNPs (r = 5, 10, 25, and 50 nm) due to the secondary electrons produced from GNPs were calculated by performing GEANT4 simulations. Finally, the DPK method, in conjunction with analytical geometry and two different DPK scaling methods (based on the linear range and physical density ratios), was applied using a numerical simulation to calculate the dose distributions around GNPs. Specifically, the point sources of electrons were randomly and uniformly sampled within a GNP and the physical path lengths traversed inside a GNP were scaled to integrate the DPK to each scoring shell outside a GNP.

Results: Both DPK scaling methods showed acceptable agreement with GEANT4 results, except at very close distances from the GNP surface. The global maximum discrepancies (200-250%) between the scaled DPK and GEANT4 results were observed within 3r from the GNP surface for all considered cases.

Conclusion: Despite its inability to accurately handle the dose perturbation in the immediate vicinity of the GNP surface, the DPK method can still be used to approximate the dose distributions around GNPs and may be found particularly useful when attempting to estimate the dose enhancement due to coated GNPs or clustered GNPs such as those present within the cellular endosomes.

Funding Support, Disclosures, and Conflict of Interest: Supported by NIH/NCI grant R01CA155446 and CPRIT grant RP160497

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