As a method of considering only significant radiation doses to different tissues, the ICRU Report 50 recommends taking the dose given to a significant tissue volume (minimum diameter greater then 15 mm) instead of choosing a single, potentially insignificant, voxel value. In order to find this significant volume, we have adapted an emission imaging analysis method to radiation therapy planning. The resulting method finds and characterizes the dose distribution in the volumes of interest in a way that includes spatial arrangement. The data can be used to signal significant hot or cold volumes in the dose plan and to score the plans based on significant dose to the tissues.