A system for determining a position of an object includes an imaging system having a x-ray source and an imager, and a processor configured to obtain a tomosynthesis image of an object using the imaging system, and determine a position of the object using the tomosynthesis image. A method of determining a position of an object includes obtaining a tomosynthesis image of an object, and determining a coordinate of the object relative to a radiation machine using the tomosynthesis image. A device for determining a position of an object includes a processor for determining a coordinate of the object relative to a radiation machine using a tomosynthesis image. A method of determining a position of an object includes obtaining an image of an object, obtaining a reference image of the object, comparing the reference image with the image, and determining a coordinate of the object based at least in part on a result of the comparing, wherein the reference image has a plane that is parallel with a plane of the image.