Abstract: A method is provided of obtaining body depth information for a patient who is lying on patient support. A patient support depth map of the upper surface of the patient support is obtained without the patient as well as an image and patient depth map of the patient on the patient support. Landmark body positions of the patient are extracted from the image so that points in a region of interest can be mapped to points of a template, using the identified landmark body positions. A body thickness is obtained for said points using the template, the depth value for the respective point and the patient support depth value for the respective point.