Markerless Motion Tracking with Simultaneous MV/kV Imaging in Spine SBRT Treatment
W Cai*, F Li, X He, P Zhang, L Cervino, X Li, T Li, Memorial Sloan Kettering Cancer Center, New York, NY
Presentations
TH-B-TRACK 6-7 (Thursday, 7/29/2021) 11:30 AM - 12:30 PM [Eastern Time (GMT-4)]
Purpose: Motion tracking with simultaneous MV/kV imaging has the distinct advantage over single kV imaging system in detecting patient motions in three dimensions in real time. This is the first report evaluating the feasibility and accuracy of the technique in markerless motion tracking for spine SBRT treatments.
Methods: First, a phantom study was carried out with clinical plans using 6FFF beam and 9 field-sliding window IMRT technique. Simultaneous MV/kV image pairs were acquired on a TrueBeam machine during beam delivery. High quality DRRs were generated using high-resolution CBCT (voxel size of 0.25mm) as the reference for matching. The MV images were taken continuously at 11.6 fps and kV images were acquired every 200MU, leading to 3~7 kV images per beam usually. Due to the limited size of the field aperture in each MV frame, an enhanced synthetic MV (ESMV) image were generated by combining multiple frames of MV images after corrections for scatters and frame intensity fluctuation. 3D translational shifts were then calculated by matching the ESMV/kV image pair to the reference DRRs based on mutual information. The motion tracking accuracy was evaluated by comparing the calculated shifts with the ground truth in the phantom study. Furthermore, the MV/kV motion tracking method was applied to two patient cases to investigate its feasibility in clinic (IRB approved).
Results: The phantom study showed maximum error of 0.4mm in three directions for all beam angles for the proposed method. For the patient cases, the image acquisitions were seamless with no impact on the normal treatment workflow. The two patient data were retrospectively analyzed and revealed a motion up to 1.1mm and 0.6mm, respectively.
Conclusion: The proposed simultaneous MV/KV markerless motion tracking technique is feasible of providing high quality orthogonal image pairs and sub-millimeter tracking accuracy in spine SBRT treatments.
Funding Support, Disclosures, and Conflict of Interest: The present study is partially supported by a research agreement with Varian Medical Systems.
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