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The Impact of Clustering in Gold Nanoparticle Dose Enhancement

P Botas Sanmartin2*, B Rudek1, J Schuemann2 , A McNamara2 , H Paganetti2 , (1) Massachusetts General Hospital & Boston University, Boston, MA, (2) Massachusetts General Hospital, Boston, MA


(Wednesday, 8/1/2018) 10:00 AM - 10:30 AM

Room: Exhibit Hall | Forum 3

Purpose: Gold nanoparticles (GNPs) promise to increase the tumor control probability by enhancing the ionizing energy deposition at nano- to micrometer distances from their surface. Previous studies have characterized the significant enhancement for single nanoparticles, but widely neglected the interplay of neighboring nanoparticles of GNP-clusters as found in cells. This study aims to quantify the impact of nanoparticle clustering on their dose enhancing properties for various sizes, concentrations and radiation modalities.

Methods: The nanoscale extension of the Geant4-based TOol for PArticle Simulation (TOPAS/TOPAS-nBio) was used to simulate radiation transport between individual GNPs and in a cell model. Electromagnetic physics processes in gold were modeled with the g4em-livermore module and interactions in water with the Geant4dna module. The electron phase-space and the deposited energy were scored. Filters on components and processes allowed tracing electron trajectories between neighboring nanoparticles.

Results: The energy deposition by secondary electrons was recorded as a function of distance from the irradiated GNP. At the surface of neighboring nanoparticles, the energy deposition went sharply up then decreased by two orders of magnitude within the gold volume. For smaller GNPs the decrease was steeper due to the smaller solid angle covered by the neighbor. The energy deposition from neighboring nanoparticles into the water environment was negligible.

Conclusion: It has been hypothesized that nanoparticle clustering could possibly induce a cascade of secondary electron emissions which could lead to greater dose enhancement than the sum of single nanoparticles. However, we found the secondary electron energy for low MeV proton irradiation to be too small to induce such cascades. Secondary electrons essentially stop within neighboring nanoparticles independent of its diameter and electrons emitted during this stopping process are absorbed on site.


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