Automation of Radiation Treatment Planning—IV. Derivation of a Mathematical Expression for the per cent Depth Dose Surface of Cobalt 60 Beams and Visualisation of Multiple Field Dose Distributions

A formula is presented for approximating the per cent depth distribution resulting from any portal size 60Co beam at 80 cm SSD. This equation may be used to obtain computer print-outs of combined multifield dose distributions as described previously (Sterling et al., 1963b), or, in a new programme, can be used to print out the combined isodose curves directly to scale with small error. A distinct geometric property of the per cent depth dose distribution is discovered and described without attempting to explain it.