Microdosimetric Evaluation on the Metallic Nanoparticle-Mediated Dose Enhancement in Radiotherapeutic Proton Irradiation

Monte Carlo simulations are performed on the dosimetric effect of metallic nanoparticles in a clinical proton irradiation. With an in-water hitting model of a single nanoparticle, the secondary electrons dose, deposited around the particle surface, is calculated for the proton irradiations in a typical spread-out Bragg peak. The dose enhancement, as the ratio of electron doses from the target particle and background water, is evaluated for the dependence on the depth of hitting, particle size, elements, coating material and thickness. The results indicate a significant dose enhancement on the particle surface within \sim100 nm, but a fast decay in further distance. The dose enhancement presents a consistency along the spread-out Bragg peak, a positive dependence on both the particle size and electron density, but a strong attenuation by surface coating. Particle cluster may increase the individual dose enhancement by electron crossfire, but is only noticeable in a compact case. The dose enhancement potentiates a radiosensitization use of metallic nanoparticles in clinical proton therapy, but challenging meanwhile with the narrow range of enhancement effect.