1. A method for determining a range of radiation, the method comprising: defining a target volume to be irradiated, the target volume characterized by a plurality of voxels; determining, without exposing the target volume to the radiation, radiation-attenuating properties that are associated with individual voxels of the plurality of voxels; deriving a range datum from the radiation-attenuating properties; and changing the range datum of a first voxel if the range datum of the first voxel differs from the range datum of two adjacent voxels.