Plenary Oral Presentations - Macquarie University Hospital

16 th International Meeting of the Leksell Gamma Knife ® SocietyMarch 2012, Sydney, AustraliaPH-242Initial performance characterization and clinicalimplementation of a novel image-guided system for Perfexion1,2Mark Ruschin, 1 Paul De Jean, 1 Steve Ansell, 1 Greg Bootsma, 1,2 Caroline Chung, 1,2 Cynthia Menard,1,2Young-Bin Cho, 1,2 David Jaffray1Radiation Medicine Program, Princess Margaret Hospital, Toronto, ON, Canada2Department of Radiation Oncology, University of Toronto, Toronto, ON, CanadaObjective: A novel cone-beam CT (CBCT) image-guidance system has been installed on a Perfexionunit at our institution and has been used for patient imaging. The purpose of this study is to describethe initial performance and clinical experience with this image-guided Perfexion (IGP) system.Methods: The initial CBCT prototype could achieve a 188-degree scan. Adjustable imaging parametersincluded: beam quality (tube potential and filter), patient dose, scan speed, reconstructionresolution, and number of projections. The optimal beam quality was determined by measuring thecontrast-to-noise ratio in known objects at different tube potentials and filter combinations. Withthe optimized beam quality, the minimum required patient dose for sufficient image quality was thendetermined by reviewing images of anthropomorphic phantoms. Target localization accuracy wasdetermined by simulating the treatment planning process in end-to-end testing in phantoms usingCBCT images defined in Gammaplan. Our initial clinical protocol was designed to allow CBCTimages of patients with brain metastases to be acquired immediately prior to and after treatment andretrospectively analyzed for setup accuracy and intra-fraction motion.Results: The optimal beam quality – taking into account contrast and patient dose – was determinedto be 90 kV with a bowtie filter plus 0.1mm copper. Using 0.5mAs per projection and 188 projections(1 per degree) resulted in a CBCT dose of approximately 1cGy to the centre of a 16cm head phantom.Low-contrast details such as polyethylene inserts (CT number=-100) in water could be detected. Highcontrast resolution of 7-8lp/cm and 3-4lp/cm was attained using 0.5mm and 1.0mm reconstructedcubic voxels respectively. The scan time was set to 1min, after which the reconstructed volume isavailable in