Dosimetric Investigation of Inverse-Optimized Proton GRID and Lattice Treatment Plans with a Clinical Pencil Beam Scanning System
M Zhu1*, H Chen2, J Snyder3, W Regine4, J Bradley1, M McDonald1, P Patel1, P Sabouri5, K Langen1, (1) Emory University School of Medicine, Atlanta, GA, (2) Emory Healthcare, Atlanta, GA, (3) University Of Alabama At Birmingham, (4) University of Maryland, Baltimore, MD, (5) Miami Cancer Institute, Miami, FL,
Presentations
PO-GePV-T-122 (Sunday, 7/25/2021) [Eastern Time (GMT-4)]
Purpose: We report inverse-optimized GRID and Lattice pencil beam scanning (PBS) proton treatment techniques and their dosimetric characteristics.
Methods: GRID and Lattice plans were created in a water phantom in a commercial treatment planning system with a clinical PBS proton system. An in-house script generated evenly spaced cylinders and spheres within a 10 cm cube centered at 10 cm from surface; the cylinder axes and the sphere lattice were positioned along the vertical direction. The diameter of the cylinders and spheres was 3 mm; patterns with 4 different center-to-center spacings were tested: 1.5 cm, 2.0 cm, 2.5 cm, and 3.0 cm. Two plans were created for each center-to-center spacing, a GRID plan and a Lattice plan, using the cylinders and the spheres as targets, respectively, with a single beam from gantry angle 0. All plans were optimized to deliver a uniform dose (15 Gy in 1 fraction) to the target while minimizing dose outside of the targets.
Results: At the depth of 10 cm (center of cube), the peak-to-valley ratios (PVRs) are 1.54, 3.47, 9.52, 26.79 for the GRID plans and 1.52, 3.26, 9.15, 22.39 for the Lattice plans for the center-to-center distances of 1.5 cm, 2.0 cm, 2.5 cm, and 3.0 cm, respectively. The ranges of PVR at different depths for the GRID plans are: 1.27-1.71, 2.48-4.32, 5.39-13.54, and 17.65-34.88, respectively. For the Lattice plans, the ranges are: 1.23-1.67, 2.33-3.90, 5.13-9.15, and 15.00-29.41, respectively.
Conclusion: Proton GRID and Lattice plans were feasible with multiple center-to-center distances. The achievable PVRs are mainly determined by the center-to-center distances for both GRID and Lattice plans. For the same center-to-center distance, GRID plans have slightly higher PVRs than the Lattice plans. The PVRs decrease with depth for both GRID and Lattice plans.
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