[Hyperfractionation--a new challenge for medical electron linear accelerators?]

In radiotherapy to an increasingly degree radiobiological aspects of the tumor behaviour during therapy are realized in daily routine. An example for this is the so called hyperfractionation of the total dose: that means multiple small fractions are applied. Doses of as low as circa 40 cGy per field are necessary. This investigation affects the constancy and the behaviour of the following beam parameters of various treatment units during the initial stage of operation (circa ten seconds): energy of bremsstrahlung, symmetry, flatness and proportionality of dose.