Choosing $FUDGEMS in EGS4 Monte Carlo

Li and Rogers describe a small but significant problems in the EGS4 Monte Carlo program. EGS4 normally overestimates the electron scattering power by redundantly taking atomic orbital electron scattering into account in two different ways. This paper shows that the two scattering models EGS4 uses can be combined consistently by setting the parameter $FUDGEMS to a fractional value. For 10 MeV electron beams in water, inconsistent use of the scattering power can result in differences of about +/-1.5% in the broad beam maximum dose.