AbstractID: 9342 Title: Application of on-line volumetric and radiographic imaging to improve set-up
in stereotactic therapy
Treatment accuracy is of paramount importance in stereotactic intra-cranial radiation therapy, where a small number (e.g.4-5) of high-dose fractions are
delivered to small lesions, often in close proximity to critical structures. A key limitation to treatment accuracy can be the introduction of positioning
errors during initial set-up of the patient. Set-up errors can include misalignments of the patient’s head inside the immobilization system, misalignment of
the immobilization system itself, and patient movement after verification of the initial set-up. In this paper we present results from an ongoing program in
our department aimed at reducing these three sources of set-up error utilizing on-line kV image-guidance. The guidance system consists of a ‘kVsource/flat-panel’ combination mounted on an Elekta linear accelerator drum with the imaging axis at right angles to the therapy axis. The system is
capable of acquiring both cone-beam CT and planar radiographs, and exhibits image quality approaching that of diagnostic x-ray systems. Online conebeam-CT and radiograph data obtained from patients undergoing radiosurgery will be presented. The focus of the presentation will, however, be on the
methods developed to utilize these data to verify and correct the set-up. Research supported by Elekta Oncology Systems.