The elimination of an artifact in the FLURZnrc-derived electron-fluence spectrum close to the Spencer-Attix-Nahum cut-off.

. An artifact in the electron fluence, differential in energy,, computed by the EGSnrc Monte-Carlo user-code FLURZnrc, was identified and a methodology has been developed to eliminate it. This artifact manifests itself as an 'unphysical' increase inat energies close to the production threshold for knock-on electrons,; this in turn causes an over-estimation of the Spencer-Attix-Nahum (SAN) 'track-end' dose by a factor ∼1.5, thereby inflating the dose derived from the SAN cavity integral. For SAN cut-off1 keV for 1 MeV and 10 MeV photons in water, aluminium and copper, with= 0.25 (default value), this anomalous increase in the SAN cavity-integral dose is of the order of 0.5%-0.7%.. The dependence ofon the value of(the maximum energy loss involved in the restricted electronic stopping power (d/d)) at or close towas investigated; this was done for different values of.The error in the electron-fluence spectrum occurs whenis setor; this error disappears (at the 0.1% level or better) ifis set ≤ 0.5 ×. However, if≤ 0.04 the error in the electron-fluence spectrum is negligible even when=.. An artifact in the FLURZnrc-derived electron fluence, differential in energy, at or close to electron energyhas been identified. It is shown how this artifact can be avoided, thereby ensuring the accurate evaluation of the SAN cavity integral.