Initial Evaluation of An MR-Compatible Phantom for Daily Imaging Quality Assurance (QA) Using a 0.35 T MR Linear Accelerator
T Romaguera1, P Perez2, V Obrien3, K Mittauer4, J McCulloch5, D Alvarez6, R Tolakanahalli7, M Chuong8, A Gutierrez9*, (1) Miami Cancer Institute, Miami, FL, (2) Miami Cancer Institute, ,,(3) Miami Cancer Institute, ,,(4) Miami Cancer Institute, Miami, FL, (5) ,Miami, FL, (6) Miami Cancer Institute, Miami, FL, (7) Miami Cancer Institute, Miami, FL, (8) MCI, Miami, FL, (9) Miami Cancer Institute, Miami, Florida
Presentations
SU-H430-IePD-F7-1 (Sunday, 7/10/2022) 4:30 PM - 5:00 PM [Eastern Time (GMT-4)]
Exhibit Hall | Forum 7
Purpose: A comprehensive QA program in radiation therapy should be inclusive of daily imaging tests as recommended by TG-142. For a volumetric imaging system, procedures that assess system collision interlocks, imaging and treatment coordinate coincidence, accuracy of positing/repositioning as well as a visual assessment of image quality are recommended to be performed daily. Considering this, an MR-compatible imaging QA phantom, based on a commercially available x-ray phantom Multiple Imaging Modality Isocentricity (MIMI), has been developed for MRgRT systems. The purpose of this study was to evaluate the MR phantom for integrity, accuracy, and use as a daily QA phantom for MRgRT systems.
Methods: A liquid-filled MR phantom with internal features similar to the commercially available MIMI phantom underwent high resolution CT and MR scans to assess structural integrity. Various TRUFI MR scans were acquired to quantify image quality. A plan was created with the isocenter placed at the center of the phantom to assess daily registration accuracy. Although the phantom has set designed offsets of 10mm, 12mm and 15mm, the phantom was also systemically displaced 10, 20, and 30mm in X,Y,Z directions using the couch. Introduced versus measured shifts were recorded. Image registrations of daily setups were performed by different users.
Results: The MR phantom showed good structural integrity and generated high quality MR images. Internal landmarks were well visualized for all protocols tested and made daily MR registrations easy to perform independent of user. Absolute mean differences between introduced and measured offsets were 0.3, 0.4, 0.1mm in X,Y,Z, respectively. For daily QA, absolute mean differences were -0.4, -0.3, -0.8mm in X,Y,Z, respectively.
Conclusion: Initial evaluation of the MR daily imaging QA phantom shows the phantom to be reproducible, efficient, and accurate for a daily IGRT QA tool. Submillimeter deviations were observed and in order with inherent MR imaging uncertainties.
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