1. A method for obtaining a contoured surface of a lesion within a patient, the method comprising the steps of: (a) providing a contoured reference surface of the lesion based on one or more images acquired at a first time; (b) generating a set of operational images of the lesion at a second time; (c) shifting the reference surface to an estimated location in the operational images; (d) segmenting the operational images based at least in part on the shifted reference surface; and (e) determining a contoured surface of the lesion at the second time based on the segmented images.