Program Information
Evaluation of Energy Absorption by Bystander Gold Nanoparticles: A Microscopic Study
J Kwon1*, K Sutherland2, A Makarova2, T Matsuura2,3, T Hashimoto4, H Peng2,5, K Umegaki2,3, H Shirato2,4, S Shimizu1,2, (1) Department of Radiation Oncology, Graduate School of Medicine, Hokkaido University, (2) Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education (GI-CoRE), Hokkaido University, (3) Division of Quantum Science and Engineering, Faculty of Engineering, Hokkaido University, (4) Department of Radiation Medicine, Graduate School of Medicine, Hokkaido University, (5) Department of Radiation Oncology, Stanford University
Presentations
SU-K-FS2-10 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: Four Seasons 2
Purpose: Gold nanoparticles (GNPs) are known to form clusters when taken up by tumor cells. In clustered GNPs, distances between GNPs get closer compared to homogeneous distributions. This closeness results in efficient electron shielding by the surrounding GNPs (bystander GNPs). The purpose of this study is to assess the energy absorption by bystander GNPs as a function of the distance between GNPs and quantify the influence of GNP size.
Methods: Energy deposition to water and absorption by GNPs were simulated with Geant4 in two steps. First, 100 keV X-rays were incident on a cylindrical GNP from a disc source. The diameter and height of the GNP, and the diameter of the source were all set to 10, 30 or 50 nm. The energy distribution of the electrons and photons escaping the GNP was scored. Second, the energy distributions were used for the source and particles were shot in a parallel direction at another (bystander) GNP, positioned 0 to 500 nm from the source. The energy deposition to the surrounding water and the energy absorption by the bystander GNP were calculated at each distance.
Results: The energy deposition to the water was reduced due to the presence of the bystander GNP when it was in the vicinity of the source. As the distance between the source and bystander GNP increased, energy absorption by the bystander GNP became lower and only 0.05% absorption remained at 500 nm from the source. Because of the increasing number of electrons entering the GNP, 50 nm diameter GNPs showed at most 4.5% greater energy absorption than 10 nm GNPs.
Conclusion: Energy absorption by the bystander GNP was observed when the distance was 500 nm or less. Our results suggest that the dose enhancement is overestimated if the energy absorption by the bystander GNPs is not considered.
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