Radiotherapy dose-fractionation schedules. Hyperfractionation and accelerated treatment regimens

It has become increasingly evident that conventional, once-daily, radiotherapy dose-fractionation schedules, developed over the years on the basis of observed normal tissue reactions, may not be ideal for all clinical situations. Differences in kinetics between normal and malignant tissues, especially repair of radiation injury in normal tissues and repopulation in tumors, suggest modifications to conventional dose-fractionation schedules that might be expected to result in an improved therapeutic ratio. Of these, hyperfractionation and accelerated treatment regimens appear to hold the most promise. The theoretical basis for these altered schedules is reviewed as is the clinical experience accumulated to date. The implications for treatment of children with brain tumors are presented.