Abstract
A simple numerical system of dosage estimation is described. By analysing the dose into primary and secondary components the dose at any point can be found quickly. Tables based on recent central axis depth dose data are presented to assist the calculations in the range 1–3·5 mm Cu H.V.L., and their use is illustrated by examples. The methods are applied to problems of moving-field therapy and are shown to offer a rapid solution to most problems of are therapy.