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.
Highlights
gold nanoparticle (GNP) are considered as potential radiosensitizers in the field of ra diation therapy [1,2,3,4,5,6], as they have been shown to enhance the bio logical radiation effectiveness in vitro and in vivo [1,6,7,8,9]
As it has come to our attention that the results reported in [26,27] are prone to be misinterpreted at representing ‘the’ dose enhancement ratios (DERs) of GNPs under diagnostic X-ray irradiation, this paper shows how much different the DERs would be for a GNP irradiated with an extended photon field
In case of secondary charged particle equilibrium (CPE), that is if the en ergy transported out of a volume by leaving electrons equals the energy introduced by electrons entering the volume, the absorbed dose is equal to the energy released in photon interactions in that volume
Summary
GNPs are considered as potential radiosensitizers in the field of ra diation therapy [1,2,3,4,5,6], as they have been shown to enhance the bio logical radiation effectiveness in vitro and in vivo [1,6,7,8,9]. This effect is often explained by a local enhancement of absorbed dose around GNPs that results from the higher absorption of radiation by the high-Z ma terial gold as compared to biological matter or water.
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