Techniques by which the quantitative anatomical data inherent in a CT scan can be directly used in treatment planning are described. The correction algorithms used in the RAD-8 system, based on an effective path length, have been extended to a pixel-by-pixel approach. By calibrating the X-ray transmission CT scanner in terms of electron densities (electron cm-3) inhomogeneity corrections may be made automatically.

A method for performing inhomogeneity corrections using a generalised Batho equation is described. The corrections are performed using the quantitative anatomical data produced by a CT scanner. The generalised Batho equation has been implemented on an EMIPLAN 7000 interactive treatment planning system. Details are given of the acquisition of the required data from the CT scan and from the existing stored beam data of the therapy machines.

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A computer system has been developed for the purpose of calculating patient treatment times and output calibration measurements and monitoring set-up conditions on a Philips RT100 superficial radiotherapy unit. With minor modifications it could be used with other superficial therapy units. The system has been developed around a Gemini Galaxy microcomputer wh ich has a Z80 processor and 64K of RAM. The software is written in BCPL, a highlevel structured language which runs under the CP/M operating system but is also available on the latest 32 bit IBM-compatible microcomputers running under the MS-DOS operating system. All programs are menudriven with facilities for returning to the start of the previous section by means of the “ESC” key. All data validated at the time of entry according to the data type and expected length or magnitude. A pROM-based system is used on the RT100 machine for calibration checks, treatment time calculations and set-up checks. This system has a safety feature in that contains two sets of identical data stored in two separate pROMs which are checked against each other before entry to the program is allowed. An additional safety feature is that the pROM data cannot be modified on this system by the system operator. The full system which includes the editor and hard-copy sections, runs on a microcomputer with Winchester or floppy disk and can be used in place of the pROM-based system if required.

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