[Which methods to minimize the time factor are substantiated by the evidence, which are unproven?].

Background: Several experimental studies and randomized clinical trials demonstrate a decrease of local tumor control with increasing overall treatment time of fractionated radiotherapy. Proliferation of clonogenic tumor cells most likely is the major mechanism underlying this phenomenon. Important progress in radiation oncology might therefore be expected from inhibition of proliferation of clonogenic cells during radiation treatment.

Methods: Possibilities to minimize the time factor are briefly discussed.

Results And Conclusions: Inhibition of proliferation of clonogenic tumor cells during irradiation by simultaneous chemotherapy, by inhibition of signal transduction pathways that stimulate proliferation, or by pharmacological inhibition of angiogenesis are scientifically interesting but currently not proven to be effective to counteract the loss of local tumor control with increasing overall treatment of fractionated irradiation. At present, the only established approach is to complete radiotherapy within a short overall treatment time, e.g. by accelerated fractionation and by prevention or compensation of unscheduled treatment gaps.