Purpose: MRgRT with high accuracy treatment planning, requires addressing MRI geometric distortion and isocenter shift which originate from magnetic field (Bo) inhomogeneities, gradient nonlinearities, and eddy currents. In this work, we investigated the correction of MRI geometric distortion and isocenter shift acquired at various gantry angles on 0.35T MRgRT systems using preconfigured correction parameters.
Methods: Two phantoms, QUASARᵀᴹ MRID³ᴰ and the Fluke 76-907 were imaged on a 0.35T MR-Linac using a clinical 3D TRUFI sequence. The images were acquired with the onboard Siemens distortion correction function turned on and off (DstOn and DstOff). In the study, the preconfigured correction parameters i.e., deformation vector field (DVFs) with extended FOV were produced for MRID3D phantom images at each gantry angle with DstOn and DstOff. MR images from both the phantoms were then corrected using the preconfigured correction parameters and brought back to their respective software for correction evaluation. The corrected images were then compared with the original images visually and with structural similarity index (SSIM).
Results: The maximum (±SD) geometric distortion of 3.17±0.02 mm and isocenter-shift of 0.49±0.3 mm were present in MRID3D phantom images with DstOff, and was partially corrected with DstOn; 0.31±0.02 mm geometric distortion and isocenter shift of 0.48±0.3 mm. After resampling with the preconfigured extended DVF phantom images, the geometric distortion was reduced to 0.18±0.02 mm and the isocenter shift was corrected to 0.14±0.05 mm. Similarly, the isocenter shift of the images acquired from the Fluke phantom was corrected from 0.51±0.3 mm to -0.08±0.1 mm using preconfigured extended DVFs.
Conclusion: The preconfigured extended DVFs were successfully applied from one phantom to the second phantom image to correct the image distortion and isocenter-shift at different gantry angles on the MR-Linac system. This gives the possibility of applying extended DVFs to correct the systematic distortion caused by imaging during MRgRT.
MRI, Geometric Distortion, Image-guided Therapy
Not Applicable / None Entered.