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Characterizing Inter-Fraction Motion Variation for Lung SBRT Patients Using 4D-CBCT Reconstructed by Simultaneous Motion Estimation and Image Reconstruction

X Huang*, Y Zhang , J Wang , UT Southwestern Medical Center, Dallas, TX


(Sunday, 7/29/2018) 4:00 PM - 4:30 PM

Room: Exhibit Hall | Forum 6

Purpose: Respiratory motion causes uncertainties in target localization for lung cancer patients treated with stereotactic body radiation therapy (SBRT). Respiratory motion patterns can vary between planning CT acquisition and different treatment fractions. The geometric difference caused by motion variation can lead to overdose for health tissue or insufficient coverage for tumor. The goal of this work is to characterize the inter-fraction respiratory motion variation in lung SBRT patients using 4D-CBCT reconstructed by simultaneous motion estimation and image reconstruction (SMEIR).

Methods: This retrospective study included eight treatment targets from seven lung SBRT patients. Projections of CBCT at each treatment fraction were sorted into 10 phases and 4D-CBCT was reconstructed by SMEIR. Motion profiles of the tumors were then extracted from SMEIR reconstructed 4D-CBCT and also from planning 4D-CT. For each groups of 4D images, 3D displacements of tumors were extracted along superior-inferior (SI), left-right (LR) and anterior-posterior (AP) directions. We used Wilcoxon signed-rank test to evaluate the tumor motion differences of the following three scenarios: 1) motion trajectories extracted from planning 4D-CT and from 4D-CBCT at any treatment fraction for each target to evaluate motion consistency between planning and treatment; 2) motion trajectories extracted from different treatment fractions for each patient to evaluate the consistency of motion pattern during the treatment course; and 3) motion range difference between planning CT and 4D-CBCT for all patients.

Results: Seven out of eight targets show significant difference between planning 4D-CT motion and 4D-CBCT motion during treatment. Only two out of eight targets show significant difference in motion patterns fraction to fraction. There is significant difference between planning CT motion range and CBCT motion range taking all eight targets into the consideration.

Conclusion: Target motion difference is significant between simulation and treatments but not between different treatment fractions.


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