S Marasini¹, H Zhang¹, B Gu¹, B Quinn², M Cole², R Flores², T Kim¹*, (1) Washington University in St. Louis, Saint Louis, MO, (2) Modus Medical Devices, Inc., London, ON, CA

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  T Kim

PO-GePV-M-260 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: MRgRT is advantageous for the treatment of diseases, where large periodic motion is present. To ensure their accurate treatment delivery, the target localization of the MR-Linac system with a large field of view (FOV) needs to be addressed properly. In this work, we presented the feasibility of large FOV MRI-QA over the routine MRI-QA procedures in 0.35T MRgRT.

Methods: Daily MRI-QA phantom for MR-Linac has a small FOV; 250 x 250 x 105 mm³ compared to Insight phantom (ModusQA): 450x450x240 mm³. So for this comparison study, we used spatial integrity phantom (Fluke 76-907 Uniformity Linearity) with FOV: 450x450x120 mm³. Both phantoms were imaged in MRI mode with TRUFI sequence. The automated Insight phantom covers the FOV in one setup without phantom movement for each orientation whereas the fluke phantom needs repositioning in different directions to cover the FOV similar to the insight phantom. The Insight phantom is comprised of two compartments; the upper vertical plate for imaging the axial and sagittal plane and the horizontal base plate for coronal plane imaging. The baseplate separately was used for the phased array coil test by placing the desired coil around the base-section.

Results: The Insight phantom captured the image artifacts across the entire planar field of view, up to 40cm, in one image acquisition, unlike the spatial integrity phantom which requires five different setups at a sagittal plane to capture those changes. Using the automated analysis, the proposed approach provided information on phantom alignment, geometric accuracy, spatial resolution, slice thickness, and image intensity uniformity. Besides this, the phased array coil was analyzed using the base plate.

Conclusion: We demonstrate the working feasibility of the large FOV MRI-QA which helps in tracking MR imaging quality over time at a much higher frequency compared to the current practice using the spatial integrity phantom.

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