A simple model of 60Co beams for computerized radiotherapy planning.

A mathematical model of the dose in tissue from a beam of 60Co gamma rays is presented which is based on a novel fitting formula for the lateral profiles, and the properties of decrement lines. Four parameters completely specify an open field, and six parameters a wedged field to a good precision, as measured by the isodose RMS error of fit. A consequence of the method is that only one lateral profile at a depth of 10 cm needs to be measured, for open and wedged fields, in order to describe the whole field. The model is suitable either for computers or programmable calculators.