Characterization of a 0.35T MR system for phantom image quality stability and in vivo assessment of motion quantification

• DOI: 10.1120/jacmp.v16i6.5353
• Publication Date: 2017-02-28T00:15:12Z
• Authors: Daniel L. Saenz; Yue Yan; Neil Christensen; Margaret A. Henzler; Lisa J. Forrest; John E. Bayouth; Bhudatt R. Paliwal
• Keywords: Phantoms, Imaging; Radiotherapy Planning, Computer-Assisted; Magnetic Resonance Imaging; Motion; 03 medical and health sciences; Dogs; Imaging, Three-Dimensional; 0302 clinical medicine; Models, Animal; Radiation Oncology Physics; Animals; Humans; Radiotherapy, Intensity-Modulated; Four-Dimensional Computed Tomography; Tomography, X-Ray Computed; Radiotherapy, Image-Guided

ViewRay is a novel MR-guided radiotherapy system capable of imaging in near real-time at four frames per second during treatment using 0.35T field strength. It allows for improved gating techniques and adaptive radiotherapy. Three cobalt-60 sources (~ 15,000 Curies) permit multiple-beam, intensity-modulated radiation therapy. The primary aim this study to assess the stability, accuracy, automatic segmentation algorithm capability track motion simulated vivo targets. Magnetic resonance (MRI) characteristics were assessed American College Radiology (ACR)-recommended phantom accreditation protocol. Images ACR acquired head coil following scanning instructions. recommended T1- T2-weighted sequences evaluated. Nine measurements performed over period seven months, on just monthly basis, establish consistency. A silicon dielectric gel target was attached motor via rod. 40 mm total amplitude used with cycles 3 9 s length sinusoidal trajectory. Trajectories six moving clinical targets canine patients quantified tracked. images analyzed, results compared acceptance levels. Measured slice thickness accuracies within limits. In 0.35 T system, image intensity uniformity also limit. Over range cycle lengths, representing wide breathing rates imaged frames/s, excellent agreement observed between expected measured trajectories. targets, including gross volume (GTV), as well other abdominal soft tissue structures, visualized inherent MR contrast, allowing preliminary tracking.