“…SI, , can still be calculated using Eqs. (3) and (4) (22) where Fhom(-*^d .^d) is the primary photon energy fluence (normalized to the central axis) at an off-axis position, {xa,yd)-P\^\ and F\1^ are the inverse-square-law correction factors for the point source and extrafocal source, respectively. They are given by…”