SU‐E‐J‐211: Assessing the Consistency of the ViewRay 0.35 T MRI System

Abstract

Purpose:ViewRay is a novel image‐guided radiotherapy approach with an integrated 0.35 T MR unit and three Cobalt‐60 heads. In order to continuously ensure the high resolution and high soft tissue contrast available in MR images, we quantified a multitude of relevant imaging parameters over a period of six months to establish its stability and imaging quality. In the assessment process, consideration is also given to the need to establish the number of tests required to have confidence in the performance of the system for radiation therapy planning applications.Methods:Daily, weekly, monthly and annual imaging tests were performed over a period of six months using standardized phantoms (a 24 cm diameter sphere and the ACR phantom) to quantify the performance of the system. In addition to the ACR and NEMA recommended tests, we also included element testing, spatial integrity, Eddy current and magnetic field inhomogeneity measurements. The ACR test is used for assessing the following parameters for T1 and T2: geometric accuracy, high contrast spatial resolution, slice thickness accuracy, slice position accuracy, percent signal ghosting, low contrast object detectability. It also includes percent image uniformity (PIU) for T1. The NEMA test is primarily designed to check SNR and PIU.Results:Over the period of six months, all the parameters were maintained within the recommendations provided in the ACR and NEMA standards. PIU and SNR were found to be sensitive to malfunctions in the components of the multileaf collimators. Details of the findings will be presented.Conclusion:The data suggests that ViewRay imaging system has functioned in a consistent and reliable manner. MR imaging from ViewRay 0.35T system complies with the ACR and NEMA recommended acceptance standards.