title: Irradiation of gold nanoparticles by x-rays: Monte Carlo simulation of dose enhancements and the spatial properties of the secondary electrons production.
abstract: OBJECTIVE
  The aim of this study is to understand the characteristics of secondary electrons generated from the interaction of gold nanoparticles (GNPs) with x-rays as a function of nanoparticle size and beam energy and thereby further the understanding of GNP-enhanced radiotherapy.
  
  
  METHODS
  The effective range, deflection angle, dose deposition, energy, and interaction processes of electrons produced from the interaction of x-rays with a GNP were calculated by Monte Carlo simulations. The GEANT4 code was used to simulate and track electrons generated from a 2, 50, and 100 nm diameter GNP when it is irradiated with a 50 kVp, 250 kVp, cobalt-60, and 6 MV photon beam in water.
  
  
  RESULTS
  When a GNP was present, depending on the beam energies used, secondary electron production was increased by 10- to 2000-fold compared to an absence of a GNP. Low-energy photon beams were much more efficient at interacting with the GNP by two to three orders of magnitude compared to MV energies and increased the deflection angle. GNPs with larger diameters also contributed more dose. The majority of the energy deposition was outside the GNP, rather than self-absorbed by the nanoparticle. The mean effective range of electron tracks for the beams tested ranged from approximately 3 microm to 1 mm.
  
  
  CONCLUSIONS
  These simulated results yield important insights concerning the spatial distributions and elevated dose in GNP-enhanced radiotherapy. The authors conclude that the irradiation of GNP at lower photon energies will be more efficient for cell killing. This conclusion is consistent with published studies.
authors: Department of Medical Biophysics, University of Toronto, Toronto, Ontario M5G 2M9, Canada.
authors: Michael K K
authors: MK
authors: Leung
authors: James C L
authors: JC
authors: Chow
authors: B Devika
authors: BD
authors: Chithrani
authors: Martin J G
authors: MJ
authors: Lee
authors: Barbara
authors: B
authors: Oms
authors: David A
authors: DA
authors: Jaffray
mesh_terms: D016923:Cell Death / Q000528:radiation effects; D004583:Electrons; D006046:Gold / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry*; D009010:Monte Carlo Method; D010316:Particle Size; D011874:Radiometry; D011878:Radiotherapy / Q000379:methods*; D014965:X-Rays
chemical_list: D006046:Gold