  In their recent article, Derrien et al. (Derrien et al., 2023) study the
anisotropy of microdosimetric quantities for spherical sites of several sizes
placed around spherical gold nanoparticles of several diameters irradiated by
monoenergetic photons. This comment points out that (1) the reported single
event distributions of specific energy may be biased due to overcounting. (2)
by considering only energy imparted by electrons produced in photon
interactions in the nanoparticle, the magnitude of the anisotropy is
overestimated by up to orders of magnitude with respect to an irradiation under
conditions of secondary particle equilibrium.
