SU-E-J-21: An Intercomparison of Imaging Performance of Two Linac-Mounted Imaging Systems Used in Radiation Therapy: TrueBeam and Trilogy.

Abstract

To evaluate and compare the performance of the imaging systems of two linear accelerators, used in radiation therapy. The study includes the following imaging components: electronic portal imaging device (EPID), kilovoltage projection imaging and kilovoltage cone-beam CT. The imaging systems mounted on the Varian Trilogy (Varian Medical Systems) and Varian TrueBeam, were evaluated. Image quality of two EPID systems (ASI-1000) and the two kV flat panel imagers (PaxScan 4030CB) was evaluated in terms of spatial resolution and contrast-to-noise ratio (CNR) using the QC-3 and QCkV-1 phantoms (Standard Imaging, Inc.). Cone-beam CT image sets of the CatPhan phantom (The Phantom Lab.) were obtained for standard dose head (100kVp, 0.4mAs per projection) and body (125kVp, 1.04mAs) protocols. Imaging parameters of the default clinical settings were used. The end points of the comparison were spatial resolution, CT number linearity, low contrast detectability and image uniformity. Analysis of all types of images was performed by the PIPSpro software (Standard Imaging). The critical frequency (f50 in units of lp/mm) of 0.446 and 0.403 were obtained for TrueBeam and Trilogy MV detectors, respectively. The CNR was found double for Trilogy. For kilo-voltage detectors the f50 was 1.337 and 1.363, while the CNR was better by 6% in Trilogy machine. The CBCT comparison showed a 30% higher uniformity index for the TrueBeam system for pelvis protocol and 50% higher head. No significant difference was found in low contrast detectability and CT number linearity and resolution, 5 lp/mm. The Trilogy image was noisier by 35% and 30% for pelvis and standard head protocol, respectively. The critical frequencies of both kV and MV detectors were found better in TrueBeam, while CNRs were found better in Trilogy. TrueBeam preformed superiorly in CBCT in terms of image uniformity and noise level.