Evaluation of QUASAR Insight Phantom for daily imaging QA of MRgRT linacs

Magnetic resonance imaging (MRI) and its importance in modern radiation therapy requires a standardized daily quality assurance (QA) procedure that is both comprehensive and efficient. Current imaging QA guidelines require a more inclusive analysis of imaging characteristics, as well as a simplification of setup procedures. We have studied the feasibility of using the Insight Phantom to provide consistent images for analyses of uniformity, slice thickness, spatial resolution, and distortion across a large field of view (FOV).

The large imaging region of the Insight Phantom was imaged using 3D True Fast Imaging with Steady State Precession (TruFi) and analyzed using the Modus QA software. The base and upright section were imaged in coronal, axial, and sagittal orientations over 3 months.

Geometric distortion analysis yielded average maximum distortions within a 210 mm diameter of 0.57, 0.73, and 0.45 mm for axial, sagittal, and coronal orientations, respectively. Similarly, within a 310 mm diameter, average maximum distortions were 0.58, 0.73, and 0.74 mm with no distortions greater than or equal to 1 mm. Average modulation transfer function (MTF) values were 0.431 ± 0.007, 0.436 ± 0.007, and 0.433 ± 0.010 lp/mm for axial, sagittal, and coronal images, respectively. Finally, slice thickness values were consistent at 2.19 ± 0.04, 2.22 ± 0.06, and 2.24 ± 0.07 mm for axial, sagittal, and coronal imaging orientations, respectively. Images were repeatable and setup procedures were quick and straightforward, enhancing therapist workflow and efficiency.

The Insight Phantom's large coverage allows a more in-depth analysis of the MRI's large FOV, and its simple setup ensures a repeatable daily QA procedure for therapists. The software also provides a comprehensive analysis of key imaging parameters in a detailed report that can be used to monitor MRI functionality and quality.