COMPUTER-BASED EXTERNAL BEAM RADIOTHERAPY PLANNING .I. - EMPIRICAL FORMULAE FOR CALCULATION OF DEPTH-DOSES

An empirical method is given which may be used for the automatic computation of isodose charts by a high-speed digital computer with an attached digital plotter. The basic physical data is derived from published tissue-air ratio tables. The procedure is valid for the principal axes of rectanglular fields, with and without wedges of constant slope, for beams of radiation from a 4 Mv linear accelerator, from 60Co units or in the H. V. T. [Half-value thickness] range 1-3 mm Cu for diaphragm-limited fields. For oblique incidence of radiation on a surface of arbitrary shape, a correction procedure equivalent to the "effective S. S. D. " [source-surface- distance] method is used, and a procedure is given to estimate the approximate depth-dose in the presence of internal inhomogenities of the body.