The first commercially available MRI‐guided IMRT (MRIGRT) system (ViewRay, Cleveland, OH) has been installed at Washington University in St. Louis. This novel medical instrument combines magnetic resonance imaging and intensity modulated radiation therapy at a single isocenter for simultaneous use during therapy along with automated tissue tracking and beam control based on images of soft tissue acquired in real time rates of 2–4 FPS simultaneous to the delivery. The purpose of this presentation is to describe and evaluate the technical aspects of the instrument as well as its adaptive and image guided radiotherapy workflows. The ViewRay system consists of a 0.35‐T double‐doughnut MRI coupled with a gantry that houses three radiotherapy heads containing 15,000‐Ci Co‐60 sources (120° apart). IMRT delivery is enabled by 3 doubly‐focused MLCs that serve as the only collimators for each head, allowing a maximum field size of 27 cm2 at the 105‐cm isocenter. MRI imaging is used prior to and during delivery for patient setup evaluation, adaptive radiotherapy, and tissue tracking and beam control based on real time 2–4 FPS imaging (2 FPS in 3 parallel planes or 4 FPS in a single plane). The fast MR imaging coupled with fast autocontouring, image fusion that can transfer tissue densities (via contours through bulk density or from fused CT imaging), and dose calculation facilitate real time dose delivery evaluation, on couch reoptimization, and replanning when necessary. The instrument's multiframe per second MR imaging enables motion correlated delivery based on the actual target volumes rather than on surrogates. Following treatment, the image, contours, and control system data produce a record of the delivery that is automatically recorded and registered to the orginal plan for evaluation. All imaging and adaptive features are controlled by clinician directives at the planning stage and can be set as required, optional, or prohibited. The design and capabilities of the system create several novel concepts and promising capabilities in RT delivery from imaging and treatment to workflow and QA/QC. This presentation discusses the initial assessment of these features and their implementation and the early clinical experience with the system including validation of its capabilities. Learning Objectives: 1. To describe technical design and capabilites of ViewRay system 2. To describe adaptive and image guided RT workflow with this system 3. To present initial validation assessment of the system.