Investigation into the effects of high-Z nano materials in proton therapy

Abstract

High-Z nano materials have been previously shown to increase the amount of dose deposition within the tumour due to an increase in secondary electrons.This study evaluates the effects of high-Z nano materials in combination with protons, and the impact of proton energy, nanoparticle material and concentration. These effects were studied in silico through Monte Carlo simulation and experimentally through a phantom study, with particular attention to macroscale changes to the Bragg peak in the presence of nanoparticles. Three nanoparticle materials were simulated (gold, silver and platinum) at three concentrations (0.01, 0.1 and 6.5 mg ml−1) at two clinical proton energies (60 and 226 MeV). Simulations were verified experimentally using Gafchromic film measurements of gold nanoparticles suspended in water at two available high concentrations (5.5 mg ml−1 and 1.1 mg ml−1). A significant change to Bragg peak features was evident, where at 226 MeV and 6.5 mg ml−1, simulations of gold showed a 4.7 mm longitudinal shift of the distal edge and experimentally at 5.5 mg ml−1, a shift of 2.2 mm. Simulations showed this effect to be material dependent, where platinum having the highest physical density caused the greatest shift with increasing concentration. A dose enhancement of 6% ± 0.05 and 5% ± 0.15 (60 MeV and 226 MeV, respectively) was evident with gold at 6.5 mg ml−1 to water alone, compared to the 21% ± 0.53 observed experimentally as dose to film with 5.5 mg ml−1 of gold nanoparticles suspended in water at 226 MeV. The introduction of nanoparticles has strong potential to enhance dose in proton therapy, however the changes to the Bragg peak distribution that occur with high concentrations need to be accounted for to ensure tumour coverage.

Metallic nanoparticles irradiated by low‐energy protons for radiation therapy: Are there significant physical effects to enhance the dose delivery?

“…Ahmad et al validated a model of proton Bragg peak shift due to the presence of metallic nanoparticles. 18 They observed a material-dependent shift of several millimeters and a narrowing of the Bragg peak in a water phantom both in silico and experimentally. Using gafchromic film, a dose enhancement up to 21% was observed at 226 MeV, although the simulated value reached only 5%.…”

Radiobiological Implications of Nanoparticles Following Radiation Treatment

“…It has been shown over the years that nanoparticles (NPs) can be used to locally enhance the level of dose deposition, [ 1 ] and even in some instances cause tumors to be more sensitive to the damaging effects of ionizing radiation. [ 2 ] Although this form of treatment has shown much promise, it is not currently used clinically due to the number of variables that need to be investigated to control and optimize the effect.…”

<p>Ultra-small gadolinium oxide nanocrystal sensitization of non-small-cell lung cancer cells toward X-ray irradiation by promoting cytostatic autophagy</p>

“…High-Z metal-based nanoparticles possess high X-ray photon capture cross-sections and are capable of increasing the production of secondary and Auger electrons, which in turn increases the generated reactive oxygen species (ROS) and enhances radiotherapy. 8,9 In addition to gold nanoparticles, which are the first and most studied nanoparticles and the enhancement effects of which have been demonstrated both in vitro and in vivo, [10][11][12] gadolinium-based nanoparticles (GdNPs) have also attracted substantial attention because of their high relaxation time and high atomic number (Z=64). [13][14][15][16] Ultra-small gadolinium oxide nanocrystals (GONs) are attractive GdNPs that possess a high density of Gd per contrastagent unit (200-400 atoms per particle).…”