CALCULATION OF DOSE IN ASYMMETRIC PHOTON FIELDS

A method is introduced to calculate monitor units to points off axis. Extensive data are presented comparing this method with measured value s of dose per monitor unit on the central ray of asymmetric fields pro duced by a variety of linear accelerators. The technique demonstrates improvement over existing methods that use large-field profile data. T he method is found to be both simple and accurate: Agreement within +/ -2% is obtained using parameters readily available within the clinic.