A radiation-treatment planning apparatus accesses first information regarding a first image that pertains to a patient's body at a first time as well as second information regarding a second image that pertains to the patient's body at a second, later time. The radiation-treatment planning apparatus then correlates components of the patient's body as appear in the second image with components that appear in the first image while treating the components as comprising rigid structures regardless of whether those components, in fact, are rigid structures. The first information can include segmentation information as pertains to the components. These teachings will accommodate a wide range of components including, but not limited to, organs, portions of organs, and even implanted man-made objects.