Program Information
A New Method to Reconstruct Intra-Fractional Liver Motion in Volumetric Modulated Arc Therapy (VMAT)
Y Chi*, C Shen , B Li , Y Zhang , T Chiu , M Yang , X Jia , The University of Texas Southwestern Medical Center, Dallas, TX
Presentations
TU-H-CAMPUS-JT-4 (Tuesday, August 1, 2017) 4:30 PM - 5:30 PM Room: Joint Imaging-Therapy ePoster Theater
Purpose: Stereotactic body radiation therapy has been used to effectively eradicate liver tumors. However, due to intra-fractional liver motion, dose discrepancy between delivered dose and prescription is a major concern. It is then critical to obtain intra-fractional liver motion information, such that advanced motion management strategies can be performed, e.g. motion tracking or dose reconstruction and adaptive replanning. The challenges are low-contrast tumor object in x-ray images, very few (typically ≤2) fiducial markers and complex tumor motion with both translational (T) and rotational (R) components. In this study, we developed a novel 6 degree-of-freedom (DoF) motion-reconstruction method for volumetric modulated arc therapy (VMAT), in which time-dependent tumor motion information was derived based on kV x-ray projections of two linear markers.
Methods: We used two gold linear markers. During a VMAT treatment, triggered kV imaging function on a Truebeam linac was used to acquire projections every 3sec. In each projection, four endpoints of the two markers were identified using image processing techniques. A Projection Marker Matching Method was developed to reconstruct the 6-DoF tumor motion information. The method determines translation and rotation by matching projections of the estimated 3D marker endpoints with corresponding identified ones. Smooth motion along temporal direction was employed as a constraint. We tested our method in both simulation and experimental studies. In the experimental tests, MV projections were also acquired, such that ground truth marker endpoints can be determined via triangulation of kV and MV images.
Results: 3D root-mean-square errors were 1.158, 0.576 and 1.247 mm for T-only, R-only and T+R motion, respectively. Rotational accuracy were -0.073±0.194, -1.123±0.707 and 0.400±0.980 degree in roll, pitch and yaw directions in the T+R motion.
Conclusion: Our method can accurately determine intra-fractional liver tumor motion (T+R) using kV projections of only two fiducial markers.
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