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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