Editorial: Post-therapeutic radiation injuries of the nervous system. Reflections on their prevention.

The introduction of the concept of Nominal Standard Dose and of Time, Dose Fractionation Factors ostensibly permits definition of tolerance doses for normal tissues in unequivocal terms. However, even with these refinements, tolerance doses remain, at best, guidelines, because radiobiologic effectiveness is governed not only by the effective dose, but also by individual factors, which will modify the response. Attention must be accorded to these biologic parameters, in order to prevent injury to healthy tissues. Of particular significance are the relative size or volume of the irradiated tissue, the possible presence of co-existing pathology in the exposed organ and the development of disease after tge termination of the treatment. Even if these factors are properly respected, the risk of radiation injury cannot entirely be eliminated. The radiotherapist is therefore obligated to use an approach which minimizes the exposure of the healthy nervous tissue, a goal which has become attainable with the advent of modern accelerators as radiation sources.