Abstract # 2550 4D CT for Hepatobiliary Malignancies: Organs at Risk and Implications for Gating

Presenter: Ma, Daniel

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Eleven patients with hepatobiliary malignancies were enrolled in a prospective trial investigating organ motion. Each patient underwent quantitative spirometry during a multislice- computed tomography (CT) following standard helical-CT simulation (Philips Brilliance 16-slice). 4D CT images were reconstructed by tidal volume, capturing end-expiration, mid-inspiration, end inspiration, and mid-expiration respiratory phases. Each CT reconstruction was fused with the standard helical-CT simulation, and the liver and kidneys in each phase of respiration were contoured for each patient. The gross-tumor volume (GTV) and clinical target volume (CTV) were first contoured on the helical CT scan, and then adjusted for target motion based on fused 4D CT scan reconstructions. Margins to consider expected treatment setup error were included to generate the planning target volume (PTV.) Each of these patients was planned using 18 MV x-rays to 50.4 Gy to the PTV, using 3D conformal therapy. Using plan parameters from RTOG P0411, the V18 for right and left kidneys and the V30 and V20 for the liver were examined at tidal inspiration and expiration

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