Program Information
Evaluation of Organ Sparing Using Simulated Tumor Tracking for Liver and Pancreas Patients with An MRI-Linac Beam Model
S Al-Ward1*, A Kim1,2 , C McCann1,2 , M Ruschin1,2 , S Myrehaug1,2 , W Chu1,2 , A Sahgal1,2 , B Keller1,2 , (1) Sunnybrook Odette Cancer Centre, Toronto, ON, Canada (2) University of Toronto, Department of radiation Oncology, Toronto, ON, Canada
Presentations
TU-L-GePD-TT-3 (Tuesday, August 1, 2017) 1:15 PM - 1:45 PM Room: Therapy ePoster Theater
Purpose: To evaluate OAR sparing for liver and pancreas patients by simulating tumor tracking using the Monaco treatment planning system for the Elekta MRI-Linac
Methods: We compared three treatment planning approaches for two SBRT patients (liver and pancreas) using Monaco with 4DCT data sets: 1) the conventional ITV method using a 6MV Elekta Agility beam, 2) a MLC tracking method which used a virtual-couch-shift (VCS) to track the GTV centroid, and segment-aperture-morphing (SAM) to account for GTV deformations 3) a MLC tracking method which tracked a MTV (moving target volume), where the MTV was created by shifting the GTV centroids at each phase to overlap with the GTV centroid at a reference phase. The MTV shape is unchanged in all phases; therefore, SAM was not needed, and only VCS was used. For both tracking methods, we used a 7MV MRI-Linac beam that simulated a transverse 1.5T magnetic field. All methods used a 5mmPTV margin. For the same PTV isocoverage, the OAR DVHs for each method were compared.
Results: Tracking methods spared more dose to OARs than the ITV method, and Method 2 spared more dose than Method 3 since the GTV is inherently smaller than the MTV (by an average of 10.36 cc). In all methods, the V95% covered 99% of the target. The maximum dose to the duodenum, bowels, kidneys, and stomach were spared by an average of 2.0 Gy, 6.7 Gy, 2.5 Gy, and 3.09 Gy respectively using Method 2, and 2.4 Gy, 3.0 Gy, 1.4 Gy, 2.4 Gy using Method 3 compared to the ITV method.
Conclusion: This preliminary work quantifies the potential benefit for an MRI-Linac tracking system to spare OARs in liver and pancreas patients using two different tracking approaches. Data on a number of patients with different tumor amplitudes will be discussed.
Funding Support, Disclosures, and Conflict of Interest: This project was made possible with the financial support of Elekta
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