ALTERED FRACTIONATION IN RADIOTHERAPY

Differences between late-responding (slowly proliferating) normal tiss ues and early-responding (rapidly proliferating) normal tissues and tu mor cells and the event of tumor cell repopulation occurring during tr eatment have essentially led to the development of altered fractionati on schemes. Altered fractionation regimens mainly refer to schedules u tilising two or more (small lose) fractions per day for part of or for the entire treatment course. It must be underlined that a true standa rd or conventional fractionation regimen does not exist: no schedule i s universally recognised as the standard of reference to be compared w ith. However, continental European and U.S, conventional regimens are the considered control arm with which the new experimental regimens ha ve to be compared. For this reason they are generally recognised as th e standards. The basic rationale for hyperfractionated or accelerated regimens respectively lies in the possibility (a) to deliver higher to tal doses reducing late-responding normal tissue damage, (b) to delive r total doses in a reduced overall treatment time to defeat tumor clon ogen repopulation. Multiple fractions per day should not be delivered with interfraction intervals smaller than 6 hours. Clinical results of phase III and limited but convincing phase III randomised trials sugg est that a therapeutic benefit can be achieved with new altered regime ns.