1. A method of obtaining a contoured surface representation of a lesion within a patient, the method comprising: obtaining a first contour representing an outer surface of the lesion at a first time prior to treatment, the first contour having been obtained from one or more planning images of the lesion acquired at the first time, the first contour including a first set of surface elements; obtaining a set of treatment images of the lesion, the treatment images having been acquired from the patient during a treatment session at a second time later than the first time, wherein the treatment images include a second set of surface elements corresponding to the lesion during the treatment session at the second time; positioning the first contour from the planning images within the set of treatment images at a location corresponding to the lesion; calculating a mapping between the first set of surface elements and the second set of surface elements; adjusting the first set of surface elements based on the calculated mapping by using the first contour as an initial estimate; obtaining, based on the adjusted first set of surface elements, a second contour of the lesion from the treatment images obtained during the treatment session, the second contour representing the outer surface of the lesion at the second time; and generating display data to present the second contour of the lesion on a display.