Current status of the CBCT project at Varian Medical Systems

摘要

Tracking and targeting the tumours are simultaneous processes in the image-guidedradiotherapy (IGRT); this is expected to boost the efficiency, the reliability, and the safety inthe treatment. Varian Medical Systems (VMS) has already produced and installed the firstIGRT machine; the device comprises the VMS Clinac equipped with the On-Board Imager(OBl) component. Cone-beam CT (CBCT) imaging, one of the options of the OBI machine,aims at high-quality volumetric reconstruction. A number of calibrations are needed in order tooperate our CT-imaging machines properly; they ensure that the machine components areproperly aligned, the mechanical distortions are small, and yield important output that is usedin the reconstruction of the actual scan data. The geometrical calibration is achieved by usinga needle phantom. In order to increase the dynamic range of our imager (hence, to obtainreliable information simultaneously in the high- and the low-attenuation areas of the irradiatedobject), VMS has developed a dual-gain mode. Next on our agenda is the suppression of(ring, streak, and beam-hardening) artefacts in our reconstructed images and the furtherdevelopment of our detectors in order to remove patterns relating to lag and ghosting effects.