The present application is directed to the idea of using sampling techniques to propagate segmentation uncertainty in order to evaluate variability in radiation planning. A radiotherapy planning apparatus (10) creates diagnostic image data of a region of interest of a subject. Image data from other sources can also be used. The image data is segmented (44) and combined with previously imaged model data. Target measures such as dose volume histograms are produced for each of the segmentations of the image data. These measures are later combined into a statistical quantification of the target measure (FIG. 3). This information is presented (52) to the user to give the user possible outcomes of the radiotherapy plan, and, e.g., confidence levels in those outcomes.