A computer implemented method of delineating an object within a volumetric medical image, the method comprising: obtaining auto-generated contour data for the object within the volumetric medical image, the auto-generated contour data defining a set of auto-generated contours forming at least one volumetric delineation structure for the object; selecting, from the set of auto-generated contours, a subset of auto-generated contours for manual editing; and wherein selecting the subset of auto-generated contours for manual editing is based on: a predefined spacing between image slices corresponding to the derived subset of auto-generated contours; and an assessment of out-of-plane curvature of auto-generated contours; presenting the subset of auto-generated contours to a user; receiving at least one indication from the user of at least one contour to be edited from the subset of auto-generated contours, the at least one indication comprises at least one of: an indication of image slices of the medical image; and an indication of the object within the medical image; receiving user feedback for each of the at least one indicated contours comprising one of: approval of the indicated contour; modification of the indicated contour; and replacement of the indicated contour with a user generated contour; and deriving a full set of contours forming a revised volumetric delineation structure for the object based at least partly on an interpolation of the at least one indicated contour for which user feedback was received; storing contour data defining the derived full set of contours forming the revised volumetric delineation structure for the object within at least one data storage device. obtaining auto-generated contour data for the object within the volumetric medical image, the auto-generated contour data defining a set of auto-generated contours forming at least one volumetric delineation structure for the object; selecting, from the set of auto-generated contours, a subset of auto-generated contours for manual editing; and wherein selecting the subset of auto-generated contours for manual editing is based on: a predefined spacing between image slices corresponding to the derived subset of auto-generated contours; and an assessment of out-of-plane curvature of auto-generated contours; a predefined spacing between image slices corresponding to the derived subset of auto-generated contours; and an assessment of out-of-plane curvature of auto-generated contours; presenting the subset of auto-generated contours to a user; receiving at least one indication from the user of at least one contour to be edited from the subset of auto-generated contours, the at least one indication comprises at least one of: an indication of image slices of the medical image; and an indication of the object within the medical image; an indication of image slices of the medical image; and an indication of the object within the medical image; receiving user feedback for each of the at least one indicated contours comprising one of: approval of the indicated contour; modification of the indicated contour; and replacement of the indicated contour with a user generated contour; approval of the indicated contour; modification of the indicated contour; and replacement of the indicated contour with a user generated contour; and deriving a full set of contours forming a revised volumetric delineation structure for the object based at least partly on an interpolation of the at least one indicated contour for which user feedback was received; storing contour data defining the derived full set of contours forming the revised volumetric delineation structure for the object within at least one data storage device.