DESCRIBING PATIENTS NORMAL TISSUE-REACTIONS - CONCERNING THE POSSIBILITY OF INDIVIDUALIZING RADIOTHERAPY DOSE PRESCRIPTIONS BASED ON POTENTIAL PREDICTIVE ASSAYS OF NORMAL TISSUE RADIOSENSITIVITY

Clinical radiotherapeutic doses are limited by the tolerance of normal tissues. Patients given a standard treatment exhibit a range of norma l tissue reactions, and a better understanding of this individual vari ation might allow for individualisation of radiotherapeutic prescripti ons, with consequent improvement in the therapeutic ratio. At present, there is no simple way to describe normal tissue reactions, which ham pers communication between clinic and laboratory and between groups fr om different centres. There is also no method for comparing the severi ty of reactions in different normal tissues. This arises largely becau se there is no definition of a ''normal'' reaction, an ''extreme'' rea ction or the particular term ''over-reactor'' (OR). This report propos es definitions for these terms, as well as a simple terminology for de scribing normal tissue reactions in patients having radiotherapy. The ''normal'' range represents the individual variation in normal tissue reactions amongst large numbers of patients treated in the same way wh ich is within clinically acceptable limits. The term ''OR'' is applied to an individual whose reaction is more severe than the normal range but also implies that this forced a major change in the radiotherapeut ic prescription or that the reactions were very severe or fatal. A ''s evere OR'' would develop serious problems with a typical radical dose, while an ''extreme OR'' would have such difficulties at a much lower dose. To describe the normal range, a numerical scale is suggested, fr om I to 5, resistant to sensitive. The term ''highly radiosensitive'' (HR) is suggested for category 5. An ''informal'' relative scale, as s uggested here, is quick and simple. It should allow comparison between different hospitals, compensate for differences in radiotherapeutic d ose and technique and allow comparison of reactions between different anatomical sites. It should be adequate for discriminating patients at the extremes of the normal range from those at the centre. It is hope d that the definitions and terminology proposed here will aid communic ation in the field of predictive testing of normal tissue radiosensiti vity. (C) 1998 Wiley-Liss, Inc.