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Abstract #4307

Improved gradient warping correction for large field-of-view imaging and application to radiation therapy planning

Paul T. Weavers1, Shengzhen Tao1, Kiaran McGee1, Joshua Trzasko1, Yunhong Shu1, Erik Tryggestad2, Ken-Pin Hwang3, Seung-Kyun Lee4, Thomas KF Foo4, and Matt Bernstein1

1Mayo Clinic, Rochester, MN, United States, 2Radiation Oncology, Mayo Clinic, Rochester, MN, United States, 3MD Anderson, Houston, TX, United States, 4GE Global Research, Niskayuna, NY, United States

Radiation therapy, especially proton beam therapy requires exacting spatial accuracy to deliver a sterilizing dose of ionizing radiation to the target volume with confidence. The superior soft tissue contrast afforded by MRI vs. CT has increased interest in using MRI for treatment planning. However, gradient non-linearities reduce the spatial accuracy of MRI. We have developed a fiducial phantom based calibration procedure to map these gradient nonlinearities on a system-specific basis and generate up to 9th order spherical harmonic coefficients for correction. These coefficients show improved spatial accuracy vs. standard 5th order, especially at distances >400mm from magnet and gradient isocenter.

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