A system (100, 150, 180) for treating a target region by directing a treatment beam towards the target region, the system comprising: a treatment bed; a treatment beam generator (20, 112) for generating a radiosurgical treatment beam; a diagnostic x-ray beam generator (30, 32, 106, 108) for generating during treatment a plurality of diagnostic beams (26, 28), each diagnostic beam being directed towards and through the target region; and an image recording device located adjacent to the treatment bed (34, 36, 104) for receiving each of the plurality of diagnostic beams after each diagnostic beam has passed through the target region, and for generating a series of 2-D diagnostic images of the target region at a same phase of a respiratory cycle, wherein each image in the series of 2-D diagnostic images corresponds to a received diagnostic beam of the plurality of diagnostic beams; and a processor to: generate a 3-D image of the patient during treatment based on the series of 2-D diagnostic images; determine the position of the target region during treatment based on a comparison of the generated 3-D image to a three dimensional pre-operative image of the target region; adjust the radiosurgical treatment beam based on the comparison of the generated 3-D image to the three dimensional pre-operative image of the target region; and energize the radiosurgical treatment beam at the same phase of the respiratory cycle; the system further comprising: a track that supports the diagnostic x-ray beam generator to move the diagnostic x-ray beam generator between one or more different positions so that the beam from the diagnostic x-ray beam generator is at a predefined non-zero angle with respect to the beam of the diagnostic x-ray beam generator at a different position; a respiratory motion detection system for sensing respiratory motion of the patient during the treatment so as to determine a respiratory cycle of said patient; and means for activating said diagnostic x-ray beam generator at the same phase of said respiratory cycle. a treatment bed; a treatment beam generator (20, 112) for generating a radiosurgical treatment beam; a diagnostic x-ray beam generator (30, 32, 106, 108) for generating during treatment a plurality of diagnostic beams (26, 28), each diagnostic beam being directed towards and through the target region; and an image recording device located adjacent to the treatment bed (34, 36, 104) for receiving each of the plurality of diagnostic beams after each diagnostic beam has passed through the target region, and for generating a series of 2-D diagnostic images of the target region at a same phase of a respiratory cycle, wherein each image in the series of 2-D diagnostic images corresponds to a received diagnostic beam of the plurality of diagnostic beams; and a processor to: generate a 3-D image of the patient during treatment based on the series of 2-D diagnostic images; determine the position of the target region during treatment based on a comparison of the generated 3-D image to a three dimensional pre-operative image of the target region; adjust the radiosurgical treatment beam based on the comparison of the generated 3-D image to the three dimensional pre-operative image of the target region; and energize the radiosurgical treatment beam at the same phase of the respiratory cycle; generate a 3-D image of the patient during treatment based on the series of 2-D diagnostic images; determine the position of the target region during treatment based on a comparison of the generated 3-D image to a three dimensional pre-operative image of the target region; adjust the radiosurgical treatment beam based on the comparison of the generated 3-D image to the three dimensional pre-operative image of the target region; and energize the radiosurgical treatment beam at the same phase of the respiratory cycle; the system further comprising: a track that supports the diagnostic x-ray beam generator to move the diagnostic x-ray beam generator between one or more different positions so that the beam from the diagnostic x-ray beam generator is at a predefined non-zero angle with respect to the beam of the diagnostic x-ray beam generator at a different position; a respiratory motion detection system for sensing respiratory motion of the patient during the treatment so as to determine a respiratory cycle of said patient; and means for activating said diagnostic x-ray beam generator at the same phase of said respiratory cycle. a track that supports the diagnostic x-ray beam generator to move the diagnostic x-ray beam generator between one or more different positions so that the beam from the diagnostic x-ray beam generator is at a predefined non-zero angle with respect to the beam of the diagnostic x-ray beam generator at a different position; a respiratory motion detection system for sensing respiratory motion of the patient during the treatment so as to determine a respiratory cycle of said patient; and means for activating said diagnostic x-ray beam generator at the same phase of said respiratory cycle.