  In our paper in Phys. Medica 69 (2020) 147-163, we reported results of a
Monte Carlo code intercomparison exercise for simulations of the dose
enhancement from a gold nanoparticle (GNP) irradiated by X-rays. 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 comment 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.
