1. A method for positioning a target in a three-dimensional CT image, the method comprising: displaying a three-dimensional CT image; receiving a selection by a user of at least one area of the three-dimensional CT image at a first viewing angle to generate a first three-dimensional description; receiving a selection by the user of at least one area of the three-dimensional CT image at a second viewing angle to generate a second three-dimensional description, wherein the angle between the first viewing angle and the second viewing angle is in a predetermined range and the first three-dimensional description and the second three-dimensional description are related to at least one of dimensions, positions, or physical attributes of the target at the corresponding viewing angle; and determining the target in the three-dimensional CT image based on the first three-dimensional description and the second three-dimensional description.