Remarks about fractionation schemes

Today a change from the orthodox "200 rad daily, 5 times per week" scheme to other improved treatment schemes is in the foreground of discussions. However, the situation is very complex and so far no distinct solution has been found. Radiobiology has recommended larger doses at less frequent intervals, but also smaller doses given more often have been used with quite good results. Several factors are important: Tumor conditions, dimensions, growth and sensitivity--reoxygenation of hypoxic tumor cells--recovery and tolerance of normal cells and, last but not least, the general state of the patient. To explain and unravel the problems an example of therapy with high-energy electrons is described. Considering four fundamental successively depending decisions an empirical system is described which may enable us to find improved treatment schemes. Finally a method is explained which makes it possible to transform a treatment scheme to a different equivalent scheme by calculating a total effective standard dose (ESD). This calculation follows exactly the isoeffect principle and makes possible a comparison of different treatment schemes using also different types of radiation.