Optimising Element Choice for Nanoparticle Radiosensitisers

TL;DR

This study uses Monte Carlo simulations to evaluate how different heavy elements in nanoparticles affect radiation dose enhancement at both macro and micro scales, revealing optimal elements like germanium and gadolinium for radiosensitization.

Contribution

It introduces a comprehensive modeling approach combining Geant4 simulations and the Local Effect Model to assess element-specific dose enhancement and biological impacts of nanoparticle radiosensitizers.

Findings

Dose enhancement correlates with atomic number but shows local maxima at Ge and Gd.

Nanoscale dose deposition depends on secondary Auger electron spectra.

Differences in elemental composition influence biological effectiveness.

Abstract

There is considerable interest in the use of heavy atom nanoparticles as theranostic contrast agents due to their high radiation cross-section compared to soft tissue. However, published studies have primarily focused on applications of gold nanoparticles. This study applies Monte Carlo radiation transport modelling using Geant4 to evaluate the macro- and micro-scale radiation dose enhancement following X-ray irradiation with both imaging and therapeutic energies on nanoparticles consisting of stable elements heavier than silicon. An approach based on the Local Effect Model was also used to assess potential biological impacts. While macroscopic dose enhancement is well predicted by simple absorption cross-sections, nanoscale dose deposition has a much more complex dependency on atomic number, with local maxima around germanium (Z=32) and gadolinium (Z=64), driven by variations in secondary Auger electron spectra, which translate into significant variations in biological effectiveness. These differences may provide a valuable tool for predicting and elucidating fundamental mechanisms of these agents as they move towards clinical application.