Room: Davidson Ballroom A
Purpose: Radioactive gold-palladium nanoparticles (Â¹â?°Â³Pd:Pd@AuNPs) represent a promising cancer brachytherapy method. In our mouse tumor experiment reported recently [https://www.ncbi.nlm.nih.gov/pubmed/29498821], the ex vivo distribution showed that AuNPs preferentially agglomerate in sphere-shaped vesicles ~1 micron radius in cytoplasm. The dosimetric property of such vesicles is of particular interest in cellular dosimetry.
Methods: The transmission electron microscopy (TEM) images were manually contoured for cytoplasm, nucleus and vesicles, which serve as the geometry input Monte Carlo (MC) simulation. The contoured vesicles were also used to setup source model. Geant4 (and Geant4-DNA) was used for simulation. Grid-packing in vesicles, AuNP was modeled as a âˆ…10 nm Â¹â?°Â³Pd core plus 20 nm gold coating. Various AuNP concentrations (represented by packing factor: 1 for full packing, 0.375, 0.125) were simulated. To compare, proton, â?´He ion and Â¹Â²C ion beams were also simulated in water at Bragg peak.
Results: Mean energies of electrons exiting the vesicle surface were 8.1 keV (4.6 keV for Auger electrons, 9.53 keV for photoelectrons) for r=800 nm vesicles fully packing and 6.4 keV (4.31keV for Auger and 7.7keV for photoelectrons) for r=500 nm vesicle loosely packing. In contrast, for high LET particles at Bragg peak, mean energies are 0.26 keV (proton and alpha particle) and 0.24 keV (carbon ion). The linear separation (representing area number density in case of vesicle and linear energy transfer (LET) in case of proton and ions) of secondary electrons is 4.17 nm for r=800 nm vesicles fully packing similar to 4.27 nm for â?´He at 1 MeV/u; 18.3 nm for r=500 nm vesicles loosely packing similar to 17.04 nm for 1 MeV proton.
Conclusion: When embedded inside vesicles, gold-palladium nanoparticles are equivalent or superior to high-LET particles (proton and â?´He) at Bragg peak in cellular dosimetry.