A BEAM GENERATION ALGORITHM FOR LINEAR ACCELERATORS WITH INDEPENDENT COLLIMATORS

A method is described of calculating the beam profiles, depth doses and output factors for asymmetric fields of radiation produced by linear accelerators with independent jaws. Values are calculated from data measured for symmetric fields. The only additional measurements required are a beam profile in air across the diagonal of the largest field size, and data on the radial variation of beam quality. Measurements on beams of 8 MV X-rays show that beam hardening in the flattening filter can alter the beam profiles by several per cent.