Although a number of methods of treatment optimization by computer have ben proposed, they have received little support. In this paper, an alternative approach is proposed based on the differentials of a treatment evaluation function with respect to wedge angle, incidence angle, entry point, and field weighting. The technique may be used in a batch-oriented computer system, or, by means of a conversational terminal, the therapist can plan a treatment with guidance from the program. Although it can be used to find global optima by a search process, it operates best as a method of improving partially-satisfactory treatments.
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 rectangular fields, with and without wedges of constant slope, for heams of radiation from a 4 hlv linear accelerator, from 60Co units or in the H.V.T. range 1-3 m m Cu for diaphragm-limited fields. For oblique incidence of radiation on a surface of arbitrary shape, a correction procedure equivalent t o the 'effective S.S.D.' method is used, and a procedure is given to estimate the approximate depth-dose in the presence of internal inhomogeneities of the body.
A method of utilizing a high-speed digital computer for the generation of accurate external beam radiotherapy dose distributions is described. Details of the system which includes corrections for non-normality of incidence and inhomogeneous tissue are given. A programme has been written which incorporates all these features together with automatic calculation and true-to-scale print-out of depth doses.
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