In HDR brachytherapy activity distributions can be achieved which were unknown in LDR brachytherapy. For this reason the classical dosage systems can only be used with caution in HDR brachytherapy.Different simple applications are used to investigate the effect of various activity distributions on dose and integrated reference air kerma.Within the classical LDR dosage systems dose and integrated reference air kerma were equivalent. Due to the possibility to "optimize" the activity distribution in HDR brachytherapy this is not longer the case. Different optimization algorithms and different optimization goals may lead to quite different activity distributions and different integrated reference air kerma values even if the source positions are the same. For target volume oriented optimization schemes a dosage system is described which is based on dose-volume-histograms.A widely accepted dosage system in HDR brachytherapy is missing. The dosage system described in this paper may be useful in solving this problem.