Characteristics of Secondary Electrons from Irradiated Gold Nanoparticle in Radiotherapy

Abstract

The effective range, maximum deflection angle, interaction parameters, and energy deposition of secondary electrons emitted from a gold nanoparticle irradiated by photon beams were calculated by means of Monte Carlo simulations. Moreover, the low-energy electrons (LEEs) with energy range of 3-20 eV, produced when a gold nanoparticle is irradiated by photon beams, were studied. The author's group used the Geant4-based computer code was used to simulate and track secondary electrons from a 100 nm diameter gold nanoparticle irradiated at monoenergetic photon beams of 35, 73.3, 660, and 1,200 keVand from 2, 50, and 100 nm diameter gold nanoparticles irradiated at polyenergetic photon beams of 50 kVp, 250 kVp, 1.25 MV, and 6 MV in water. To investigate the LEEs, secondary electrons emitted from a gold nanoparticle with diameter of 100 nm, interacting with photon beams with energies equal to 35, 73.3, and 600 keV, were simulated using the Geant4 code. The phase spaces of the secondary electrons produced by simulations were then used to simulate the LEEs in water using the NOREC Monte Carlo code. All secondary electrons emitted by the gold nanoparticle and all LEEs produced by each secondary electron were tracked in simulations. The author's group compared the number of secondary electron emitted with and without the gold nanoparticle in water and found that the presence of gold produces more electrons, when irradiated by monoenergetic photon beams with particularly low energy (35 keV). As the photon beam energy was increased from 35 to 1,200 keV, the effective electron range increased from 24.7 to 5,060 mm, but the total number of emitted photoelectric electrons decreased by a factor of 270 per interacting photon. The maximum electron deflection angle relative to the incident beam decreased from 83.1 to 39.2 , and the stopping power of the emitted electron decreased from 1.42 to 0.24 keV/mm. For polyenergetic photon beams with 2, 50, and 100 nm diameter nanoparticles, the author's group found that both irradiations of the 50 and 250 kVp photon beam caused significantly greater deposited energy surrounding the gold nanoparticle (three orders of magnitude) than the MV beams (approximately five times). The author's group also found that a larger portion of deposited energy resided within a larger nanoparticle under the photon irradiation. From the LEE results, the author's group found that the energy distributions of the LEEs from the gold nanoparticle do not vary significantly between different photon beam energies. In addition, the 660 keV photon beam produced more LEEs traveling 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. These simulated results yield important insights concerning the enhancement of tumor cell killing in gold nanoparticle-enhanced radiotherapy. The aim of this chapter is to show that the irradiation of gold nanoparticles at lower monoenergetic and polye...

Nanodiamond Effects on Cancer Cell Radiosensitivity: The Interplay between Their Chemical/Physical Characteristics and the Irradiation Energy

“…In this case, the high atomic number (Z) of the metallic nanoparticles gives them a significantly higher X-ray mass energy-absorption coefficient compared to biological tissues [46]. These effects were maximized after exposure to low linear energy transfer (LET) radiation in the range of kilovoltage photon energy [47], where the predominant physical interaction between photons and nanoparticles is the photoelectric effect. In our study, where 240 nm H-NDs were able to radiosensitise cells in combination with 5 Gy of γ-rays at 1.25 MeV, the Compton effect was predominant in driving the photon radiation-matter interaction.…”