Cumulative radiation effect. Part VII: computer calculations and applications in clinical practice.

In five previous papers, the concept of the Cumulative Radiation Effect (CRE) has been presented as a scale of accumulative sub-tolerance radiation damage. The biological effect generated in normal connective tissue by fractionated or continuous radiation therapy given in any temporal arrangement is described by the CRE on a unified scale of assessment, so that a unique value of the CRE describes a specific level of radiation effect. The basic methods of evaluating CREs were shown in the papers to facilitate a full understanding of the fundamental aspects of the CRE-system, but these methods can be time-consuming and tedious for complex situations. In the previous papers in this series, one way of overcoming the difficulties in evaluating CRE problems was presented in simple nomographic and tabular methods for the solution of practical problems. An alternative way of overcoming the difficulties in the evaluation of CRE problems is to use computers and it is the purpose of this paper to outline computer calculations and applications in clinical practice in connection with the CRE-system. In a general appraisal of the applications of computers to the CRE-system, the various problems encountered in clinical radiotherapy are categorised into those involving the evaluation of a CRE at a point in tissue and those involving the calculation of CRE distributions. As a general guide, the computer techniques adopted at the Glasgow Institute of Radiotherapeutics for the solution of CRE problems are presented, and consist basically of a package of three interactive programs for point CRE calculations and a Fortan program which calculates CRE distributions for iso-effect treatment planning. Many examples are given to demonstrate the applications of these programs, and special emphasis has been laid on the problem of treating a point in tissue with different doses per fraction on alternate treatment days. The wide range of possible clinical applications of the CRE-system has been outlined and described under the categories of routine clinical applicatons, retrospective and prospective surveys of patient treatment, and experimental and theoretical research. Some of these applications such as the results of surveys and studies of time optimisation of treatment schedules could have far-reaching consequences and lead to significant improvements in treatment and cure rates with the minimum damage to normal tissue.