Imaging and Plan Workflow in a Novel Low-Field Magnetic Resonance Imaging (MRI) Radiotherapy Device

Recently, Viewray Inc (Cleveland, OH) has released the RenaissanceTM System 1000, which consists of the combination of an open, split solenoid 0.35 T MRI scanner that is equipped for parallel imaging with a 60Co gamma-ray radiation treatment unit. The MRI scanner is required to be a low field unit to allow for imaging with spatial integrity by limiting magnetic susceptibility artifacts due to the patient and to prevent significant perturbations of the dose distribution. The 0.35 T magnet is a variant of the Siemens MAGNETOM product used for intraoperative imaging.

A previous study of pilot imaging using this device without the 60Co sources was completed in 2012 (HRPO# 201105295). In this study, a total of 26 patients were imaged with the device. Fourteen of these patients also had onboard CT imaging (OB-CT) where the two sets of imaging and relative organs at risk (OARs) could be compared. Fifteen to 24 OARs were evaluated per anatomical site. In total, 221 OARs and 10 target structures were compared for visualization on MRI and OB-CT image sets by each physician. At least 2/3 physicians evaluated MRI as offering better visualization for 71% of structures, OB-CT offering better visualization for 10% of structures, and both offering equivalent visualization for 14% of structures. Physicians agreed unanimously for 74% and in majority for >99% of structures evaluated, respectively. For <1% of structures, no consensus was reached. Targets were better visualized on MRI in 4/10 cases, and were never better visualized on OB-CT images.

There were limitations to this prior study. The patients were not imaged in immobilization devices that are commonly used in radiation therapy. This precluded the creation of a mock radiation therapy plan using the device for these patients. Also, the device was not evaluated in the context of radiation therapy decision making, such as patient shifts, target localization and patient repositioning.

The purpose of this study is to evaluate the imaging and plan workflow for radiation therapy utilizing this novel device. For this protocol, only the MRI scanner of the machine will be utilized. The 60Co portion of the machine capable of radiation treatment administration will not be utilized, and there will be no experimental treatments or modifications to each patient's standard of care radiation treatment plan.