A contouring processor transmits contour data to a radiotherapy device, and uses a key generated by a key generator, which identifies a target volume to be irradiated. The contouring processor is designed to access a contour database in order to acquire reference contour data in reference images relating to the target volume for determining the contour data. The contouring processor has a calculation processor designed to calculate volume percentiles from the acquired reference contour data and to emit them on a user interface to determine the contour data.
