  In their article published in Phys. Med. Biol. 59 (2014) 7675-7689, Lin et al
studied the dose enhancement of of gold nanoparticles (GNPs) for proton
therapy, which they compared with the case of photon irradiation. This comment
points out two caveats to the methodlogy used by Lin et al that may not be
evident to readers and may contribute to confusion in the literature about the
dose enhancement by gold nanoparticles.
