High-Resolution Spine Digital Reconstructed Radiograph (DRR) for Motion Tracking in Paraspinal Treatment
W Cai*, F Li, X He, P Zhang, X Li, T Li, Memorial Sloan Kettering Cancer Institute, New York, NY
Presentations
PO-GePV-M-146 (Sunday, 7/25/2021) [Eastern Time (GMT-4)]
Purpose: High quality DRR is essential to image-based motion tracking systems. In this work, we propose a method of creating high-resolution digital reconstructed radiograph (DRR) to facilitate image registration for a recently developed MV-KV imaging-based motion tracking system for paraspinal SBRT treatments.
Methods: High-resolution spine-only DRRs were computed by incorporating planning CT information into high-resolution CBCT reconstructions. Varian’s proprietary software iTools Reconstruction can reconstruct with an isotropic voxel size as small as 0.25mm, which is comparable to kV image resolution. A major challenge is to segment bones from CBCT because of its high noise level and numerous artifacts. Our strategy is to create a binary bone mask using planning CT images as they have much better image quality. The mask defines the volumes occupied by bones in CT, and in CBCT as well, provided that the patient is set up well against planning CT. Major steps of creating bone mask include: (1) Identify CBCT volume in CT; (2) Apply a soft threshold to extract cortical bones; and (3) Connect mask edges using convex hull. Bone volumes are segmented by multiply CBCT with the mask and are then projected to create bone-only DRRs from desired gantry angles using a detector pixel-driven approach.
Results: The quality of DRRs indicated that high noise level and artifacts associated with high-resolution CBCT did not impact DRR quality. Compared to DRR created from CT sim, the high spatial resolution CBCT created DRRs sharper and show more anatomic details. High-resolution DRR profiles represent actual KV image profiles well. DRR-to-KV registration uncertainties are generally around 0.25mm.
Conclusion: The proposed method is able to produce DRRs with a resolution and image quality comparable to kV images, which makes it possible for achieving sub-millimeter tracking accuracy for paraspinal SBRT.
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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