Analytic calculation of electron beam isodose distributions

Analytical techniques have been developed to generate electron beam isodose distributions from a modest set of experimental data. These techniques include (1) development of a compact yet powerful linear least-squares optimization program with a graphic display of the results, (2) coordinate transformations to allow straightforward fitting of the isodose distributions with simple polynomial functions, and (3) accurate interpolation methods to allow production of treatment planning dose matrices. The program, written in FORTRAN, has been implemented on a minicomputer and uses the standard peripherals of a commercially available treatment planning system (AECL TP-11). The computer-generated isodose and central-axis distributions correspond very closely with the data for electron energies from 5 to 20 MeV and for all field sizes.