Monte Carlo simulation on low-energy electrons from gold nanoparticle in radiotherapy

This study investigated the low-energy electrons (LEEs) produced when a gold nanoparticle (GNP) is irradiated by photon beams. The secondary electrons emitted from a GNP (diameter 100 nm), interacting with photon beams with energies equal to 35, 73.3 and 600 keV, were simulated using the Geant4 Monte Carlo code. The phase spaces of the secondary electrons were then used to simulate the LEEs in water using the NOREC Monte Carlo code. All secondary electrons emitted by the GNP, and all LEEs produced by each secondary electron were tracked in Monte Carlo simulations. It is found that the energy distributions of the LEEs from the GNP do not vary significantly between different photon beam energies. Moreover, the 660 keV photon beam produced more LEEs travelling to a longer range than photon beams of lower energies (35 and 73.3 keV). This higher energy deposition and longer range LEEs produced by the 660 keV photon beam can enhance the cell kill. Based on our Monte Carlo results, it is concluded that the unexpected close of the radiosensitization enhancement factors of the 35 (1.66) and 660 keV (1.18) photon beams from our previous measurements is because of the cell kill enhancement with the increased LEE yield and range in the 660 keV photon beam.