Intercomparison of Monte Carlo calculated dose enhancement ratios for gold nanoparticles irradiated by X-rays: Assessing the uncertainty and correct methodology for extended beams

Abstract

Results of a Monte Carlo code intercomparison exercise for simulations of the dose enhancement from a gold nanoparticle (GNP) irradiated by X-rays have been recently reported. To highlight potential differences between codes, the dose enhancement ratios (DERs) were shown for the narrow-beam geometry used in the simulations, which leads to values significantly higher than unity over distances in the order of several tens of micrometers from the GNP surface. As it has come to our attention that the figures in our paper have given rise to misinterpretation as showing 'the' DERs of GNPs under diagnostic X-ray irradiation, this article presents estimates of the DERs that would have been obtained with realistic radiation field extensions and presence of secondary particle equilibrium (SPE). These DER values are much smaller than those for a narrow-beam irradiation shown in our paper, and significant dose enhancement is only found within a few hundred nanometers around the GNP. The approach used to obtain these estimates required the development of a methodology to identify and, where possible, correct results from simulations whose implementation deviated from the initial exercise definition. Based on this methodology, literature on Monte Carlo simulated DERs has been critically assessed.

Breast radiotherapy with kilovoltage photons and gold nanoparticles as radiosensitizer: An in vitro study

“…The above findings (specifically at 6 MV) might find confirmation and some understanding in terms of the recent literature on in silico studies, [46][47][48] as refers to 15 nm AuNPs, with the distinction that the observed DEF values are in line with the available literature, but they were obtained at lower AuNPs concentrations. Future work in our new kV breast RT project will show if higher concentrations in vivo produce significantly higher DEF and SER values at MV as well as kV photon energies.…”

“…Finally, our still‐ and time‐resolved cell microscopy observations point toward a very significant presence of AuNPs clustering in cellular vesicles, where AuNPs clusters form and disrupt with a time scale in the order of tens of seconds: an effect which deserves further investigation on the radio‐sensitization efficiency and possible shielding of low‐energy secondary electrons, for a given AuNPs concentration in the cell culture medium. 48 …”

Consistency checks of results from a Monte Carlo code intercomparison for emitted electron spectra and energy deposition around a single gold nanoparticle irradiated by X-rays

“…energy range contribute negligibly to the total energy transported out of the GNP (see supplementary Fig. S1), but are relevant for the local dose increase in the proximity of the GNP ( Rabus et al 2021b).…”

“…First results from the exercise have been reported by Li et al ( 2020aLi et al ( , 2020b and the relation of the DER values with those relevant for realistic irradiation scenarios with extended photon beams have been discussed by Rabus et al ( 2019Rabus et al ( , 2021b. This work focusses on the methodology used in the assessment of the reported results for consistency between the different cases (GNP sizes, X-ray spectra) and for consistency with the principle of energy conservation.…”

Radiation Enhancer Effect of Platinum Nanoparticles in Breast Cancer Cell Lines: In Vitro and In Silico Analyses

“…Other important aspects of the localized energy deposition at the nanometer scale around the NP and their biological consequences have been recently summarized in H. Rabus et al [ 28 ]. In this paper, it is shown that the calculated DEF corresponds to a ~10 ionization in the immediate vicinity of the GNP.…”