10 MV x-ray SMRs obtained using zero-area S(p) correction factors derived by means of the Bjärngard-Petti method.

Based on the Khan concept, a new set of 10 MV x-ray scatter-maximum ratios (SMRs) has been produced. THese new SMRs reflect no electron contamination and are parametrized. A method has been developed for determining the minimum field size with lateral CPE (charged particle equilibrium) at the field centre. It is found that for 10 MV x-rays the minimum square field with lateral CPE at large depths on the central axis in water is 3.5 x 3.5 cm2. The zero-area phantom scatter correction factor (S(p)) is derived using the Bjärngard-Petti method. It is found that the effect of electron contamination is to reduce the zero-area Sp correction factor.