A simple metric, the mean absolute dose deviation (“MADD”), for characterizing dose-volume histograms (“DVH”) is disclosed. The MADD facilitates the use and the comparison of DVHs. The MADD is defined as the average of absolute differences between all points of a DVH and a dose point of a specified reference dose range. The MADD is a generalized metric free from distribution assumptions, and it is directly applicable to all types of structures.