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A Novel Method to Generate On-Board 4D MRI Using Prior 4D MRI and On-Board Limited Angle KV Projections From a Conventional LINAC for Liver SBRT Target Localization

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W Harris

W Harris*, C Wang , F Yin , J Cai , L Ren , Duke University Medical Center, Durham, NC


TU-FG-FS2-1 (Tuesday, August 1, 2017) 1:45 PM - 3:45 PM Room: Four Seasons 2

Purpose: On-board MRI is beneficial for liver SBRT localization due to its superb soft tissue contrast. However, its availability in clinics is limited. This study aims to develop a novel technique using conventional LINAC kV imaging to generate on-board 4D-MRI based on prior 4D-MRI, deformation models and on-board limited angle kV projections.

Methods: 4D-MRI volumes were acquired during patient simulation and used as prior images. The end-of-exhalation(EOE) phase of the prior 4D-MRI (MRIprior) was used to generate a synthetic CT at EOE phase (sCTprior). Patient on-board volume at any respiratory phase was considered a deformation of sCTprior. The deformation-field-map(DFM) was solved by matching DRRs of the deformed sCTprior to on-board orthogonal-view 30° scan angle kV projections using a previously developed motion-modeling and free-form deformation (MMFD) optimization algorithm. The on-board 4D-MRI was generated by deforming the MRIprior based on the DFM solved. The method was evaluated using a 4D anthropomorphic phantom (XCAT) with our in-house XCAT-MRI package to simulate prior 4D-MRI. On-board ground-truth 4D-MRI and 4D-CT were simulated with various breathing pattern changes from simulation to treatment. The effect of noise on the projections was also evaluated. A liver SBRT patient case with 4D-MRI and 4D-CT was also evaluated.

Results: For XCAT, the Volume-Percent-Difference(VPD)/Center-of-Mass-Shift(COMS) for the XCAT scenario with no breathing pattern change was 6.72%/0.45mm and 7.70%/0.55mm for EOE and EOI phases, respectively. The VPD/COMS for XCAT scenario with motion amplitude change was 6.72%/0.45mm and 5.68%/0.33mm for EOE and EOI phases, respectively. The method was robust against various levels of noise. On-board 4D-MRI was also generated successfully for the liver patient case.

Conclusion: The method successfully generated on-board 4D-MRI using prior 4D-MRI and on-board limited angle kV projections. The preliminary results show great potential for MRI-based image guidance for liver SBRT using only a kV imaging system on a conventional LINAC.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by the National Institutes of Health Grant No. R01-CA184173 and a research grant from Varian Medical Systems.

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