An assembly of hardware/software devices intended to employ stereo vision techniques to image and reconstruct three-dimensional (3-D) surfaces of a patient, projected via digital video cameras strategically configured within a treatment room which focus on the patient, to aid in the correct positioning of the patient and track events during a diagnostic imaging, treatment planning, or radiation therapy procedure. A hardware interface is used between the camera system and the CT or linear accelerator to facilitate gated capture or delivery of diagnostic or therapeutic radiation, respectively. It typically includes two or three cameras, a workstation with image display monitors and software.