A widely applicable method for computing dose distributions from external megavoltage beams

A method of computing megavoltage dose distributions using an empirical mathematical model is described. The dose at a point in a medium is calculated as the product of a central axis percentage depth dose, a crossplot factor and a wedge factor. For a given set of conditions (i.e. type of machine, source-skin distance and wedge) 16 parameters are required to calculate the values of the three factors and hence the dose at any point. These parameters can be obtained from a relatively small number of experimental measurements. Dose distributions from a variety of different treatment machines have been computed by the method and some comparisons of the calculated and measured doses have been made using 'Goodness of Fit' score values. These showed that the use of the method as a basis for computer treatment should be clinically acceptable. (author)