Program Information
Trajectory Modulated Arc Delivery for Craniospinal Irradiation: Design and Implementation of Optimal Trajectories with Dynamic Couch Motion
S Khan1*, E Chin2, N Kovalchuk1, L Xing1, D Hristov1 B Fahimian1, (1) Stanford Univ School of Medicine, Stanford, CA (2) BCCA- Vancouver Island Centre, Victoria, BC
Presentations
WE-RAM3-GePD-T-5 (Wednesday, August 2, 2017) 10:30 AM - 11:00 AM Room: Therapy ePoster Lounge
Purpose: To enhance the dose conformity and delivery efficiency of extended volume treatments such as Craniospinal Irradiation (CSI) by integration of dynamic couch motion on conventional C-arm linacs.
Methods: To enable efficient modulation beyond the limitations of multi-isocenter VMAT, we designed a Trajectory Modulated Arc Therapy (TMAT) technique for CSI treatments in a single automated trajectory through concerted time-varying gantry and couch motion. Treatment planning platform, based on the generalized form of direct aperture optimization, was developed in MATLAB to optimize dynamic MLC apertures and associated cumulative beam-on times. Multi-isocenter VMAT plan was created using posterior partial arcs, each with 60-deg variations on either side of the patient, for spinal target and 2 full arcs for cranium. Additionally, two TMAT trajectories with simultaneous gantry and couch motion were designed with respective 10 and 16 non-overlapping arc segments, sweeping back and forth posteriorly on either side of patient. The TMAT trajectories were specifically configured to provide segments that were connected throughout the delivery. The effects of novel TMAT non-collisional trajectories were evaluated. TMAT planning results were then compared to VMAT plans within the same optimization environment.
Results: For large CSI target volumes, dose conformity is analyzed based on the slice-by-slice variations in 100% dose volume and compared with VMAT. Results demonstrated 11% improvement in FWHM of distribution as compared to VMAT while 16-segment TMAT shows a significant 45% improvement, making it the optimal design for this study. Also, mean dose comparison shows a reduction of up to 14 % in lungs, 25% in lenses, 46% for parotids and other critical organs as compared to VMAT.
Conclusion: In comparison to VMAT requiring multi-isocenter arcs and abrupt couch motions between arcs, TMAT enables delivery in a single automated irradiation of the extended CSI volume. Enhanced modulation and geometrical sampling enables enhanced dose sparing.
Funding Support, Disclosures, and Conflict of Interest: This research was partially supported by a research grant from Varian Medical Systems
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