Markerless motion tracking with simultaneous MV and kV imaging in spine SBRT treatment—a feasibility study

Abstract

Objective: Motion tracking with simultaneous MV-kV imaging has distinct advantages over single kV systems. This research is a feasibility study of utilizing this technique for spine SBRT through phantom and patient studies. Approach: A clinical spine SBRT plan was developed using 6xFFF beams and nine sliding-window IMRT fields. The plan was delivered to a chest phantom on a linear accelerator. Simultaneous MV-kV image pairs were acquired during beam delivery. KV images were triggered at predefined intervals, and synthetic MV images showing enlarged MLC apertures were created by combining multiple raw MV frames with corrections for scattering and intensity variation. DRR templates were generated using high-resolution CBCT reconstructions (isotropic voxel size (0.243mm)3) as the reference for 2D-2D matching. 3D shifts were calculated from triangulation of kV-to-DRR and MV-to-DRR registrations. To evaluate tracking accuracy, detected shifts were compared to known phantom shifts as introduced before treatment. The patient study included a T-spine patient and an L-spine patient. Patient datasets were retrospectively analyzed to demonstrate the performance in clinical settings. Main Results: The treatment plan was delivered to the phantom in five scenarios: no shift, 2mm shift in one of the longitudinal, lateral and vertical directions, and 2mm shift in all the three directions. The calculated 3D shifts agreed well with the actual couch shifts, and overall, the uncertainty of 3D detection is estimated to be 0.3mm. The patient study revealed that with clinical patient image quality, the calculated 3D motion agreed with the post-treatment cone beam CT. It is feasible to automate both kV-to-DRR and MV-to-DRR registrations using a mutual information-based method, and the difference from manual registration is generally less than 0.3mm. Significance: The MV-kV imaging-based markerless motion tracking technique was validated through a feasibility study. It is a step forward toward effective motion tracking and accurate delivery for spinal SBRT.

Toward quantitative intrafractional monitoring in paraspinal SBRT using a proprietary software application: clinical implementation and patient results

“…The IMRimage's inability of capturing the patient motion in the direction along the KV beam axis can be consequential in dosimetry. In another publication, we have demonstrated the feasibility of combing IMR images with MV images of treatment beams to achieve 3D motion tracking (Cai et al 2023). However, limitation in computation latency currently does not support its use in a clinical setting and is currently being actively worked upon.…”

“…To improve the software's tracking performance, the use of highresolution DRR is helpful. These can be achieved via either CT stimulation using 1 mm slice thickness or highresolution reconstruction (Cai et al 2023), or a combination of both. Finally, the software can be enhanced to allow 3D motion tracking via triangulation of the 2D tracking results of two neighboring beams.…”