>>Performance evaluation of a CyberKnife® G4 image-guided robotic stereotactic radiosurgery system
2008 Phys. Med. Biol. 53 4697-4718 doi: 10.1088/0031-9155/53/17/016
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1 Medical Physics Department, Iatropolis, Magnitiki Tomografia, Clinic and Diagnostic Center, Ethnikis Antistaseos 54-56, 15231 Athens, Greece
2 Department of Radiology, Aretaieion Hospital, University of Athens, Vas Sophias 56, 11528 Athens, Greece
E-mail: cantypas@med.uoa.gr
Abstract. The aim of the current work was to present the performance evaluation procedures implemented at our department for the commissioning of a G4 CyberKnife system. This system consists of a robotic manipulator, a target-locating system and a lightweight 6-MV linac. Individual quality assurance procedures were performed for each of the CyberKnife subsystems. The system was checked for the mechanical accuracy of its robotic manipulator. The performance of the target-locating system was evaluated in terms of mechanical accuracy of both cameras' alignment and quality assurance tests of the x-ray generators and the flat-panel detectors. The traditional linac 6-MV beam characteristics and beam output parameters were also measured. Results revealed a manipulator mechanical mean accuracy of ~0.1 mm, with individual maximum position uncertainties less than 0.25 mm. The target-locating system mechanical accuracy was found within the acceptance limits. For the most clinically used parameters in the CyberKnife practice, e.g. 100–120 kV and 50–200 ms, kV and exposure time accuracy error were measured as less than 2%, while the precision error of the kV was determined as less than 1%. The acquired images of the ETR grid pattern revealed no geometrical distortion while the critical frequency f50 values for cameras A and B were calculated as 1.5 lp mm-1 and 1.4 lp mm-1, respectively. Dose placement measurements were performed in a head and neck phantom. Results revealed sub-millimeter beam delivery precision whereas the total clinical accuracy of the system was measured equal to 0.44 ± 0.12 mm, 0.29 ± 0.10 mm and 0.53 ± 0.16 mm for the skull, fiducial and Xsight spine tracking methods, respectively. The results of this work certify the G4 CyberKnife SRS system capable of delivering high dose distributions with sub-millimeter accuracy and precision to intracranial and extracranial lesions. Moreover, total clinical accuracy of the investigated G4 system was found to be improved for the skull and fiducial tracking methods and was comparable for Xsight spine tracking method compared with the earlier generation of the instrument.
Print publication: Issue 17 (7 September 2008)
Received 6 February 2008, in final form 3 June 2008
Published 11 August 2008
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