(Sunday, 7/14/2019) 4:00 PM - 5:00 PM
Room: Stars at Night Ballroom 2-3
Purpose: Although magnetic resonance imaging (MRI) guided radiotherapy (MRgRT) provides real-time 2D cine image, only fixed-angle 2D cine imaging is available, missing out-of-plane tumor motion and beam eye’s view (BEV). This study explores the feasibility of rotating 2D cine along the longitudinal axis through the isocenter, providing projected tumor shape in the BEV.
Methods: Rotating 2D cine images with projected tumor contours were simulated based on time-resolved (TR) and respiratory-correlated (RC) 4DMRI to guide treatment delivery of intensity-modulated radiotherapy (IMRT) or volume-modulated arc therapy (VMAT). A computational tool was built in MatLab to simulate the BEV in conjunction with the gantry rotation in an IMRT/VMAT plan. The TR-4DMRI and RC-4DMRI images of three patients scanned under an IRB-approved protocol were used to illustrate the proof of principle and the contours of gross tumor volumes (GTVs) were projected to the BEV cine from parallel slices perpendicular to the beam. The union of GTV projections was calculated to compare with the BEV beam aperture, ensuring tumor coverage. Rigid 2D-3D image matching between the BEV slice and 4DMRI library identifies the breathing state and 2D-3D GTV matching determines the GTV position relative to the cine slice.
Results: The overlay of GTV contours projected on the BEV cine provides the GTV shape seen by the radiation beam as the BEV. The spacing of parallel slices to the BEV determines the resolution of projected GTV edge. The GTV shape varies substantially in different co-planar views and the outmost GTV area on the BEV cine differs by 13%, 22%, and 44% in the three patients.
Conclusion: The simulation study demonstrates the benefit of rotating BEV cine in tracking tumor motion by visualizing tumor shape and beam aperture. Clinical implementation of this BEV approach may require additional pulse programming and real-time communication within an MRgRT system.
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