Main Session
Sep
29
PQA 05 - Physics
Presenter(s)
Xin Tong, PhD - University of Kansas Medical Center, Kansas City, KS
X. Tong1, Y. N. Zhu2, N. Shinde3, W. Li1, W. Zhang1, C. Wang4, Y. Lin5, and H. Gao5; 1Department of Radiation Oncology, University of Kansas Medical Center, Kansas City, KS, 2School of Mathematics, Harbin Institute of Technology, Harbin, China, 3University of Texas Southwestern Medical Center, Dallas, TX, 4College of Science, China Agricultural University, Beijing, China, 5Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX
Purpose/Objective(s):
Proton LATTICE (pLATTICE) therapy delivers spatially heterogeneous dose distributions by embedding high-dose peaks within low-dose valleys. Conventional pLATTICE planning typically assigns multiple beam angles to each peak, making peak localization highly sensitive to proton range uncertainty and intrafraction motion. Misalignment of dose contributions can shift peaks and degrade geometric fidelity. We propose a single-field-each-peak (SFEP) optimization strategy that assigns each peak to one optimally selected field to enhance motion robustness and reduce uncertainty-driven displacement.Materials/Methods:
In SFEP, each lattice vertex is assigned to a single field chosen from a predefined set of candidate orientations. The problem is formulated as a mixed-integer optimization model, with binary variables governing peak-to-field assignment and continuous variables optimizing proton spot weights. Field selection and dose optimization are solved jointly using an alternating-direction method of multipliers with iterative convex relaxation, enabling efficient and coordinated optimization.Results:
SFEP generated pLATTICE plans in which each peak was delivered by one automatically selected field while preserving target peak geometry. Spatial accuracy and peak-to-valley dose metrics were comparable to exhaustive search–based assignments. Under robustness evaluation (3.5% range and 5 mm setup uncertainties), SFEP demonstrated smaller variations in peak dose and localization compared with IMPT-based pLATTICE. In motion-shift simulations of an abdominal case, prescription-dose peak coverage decreased from 100% to 82.5% with SFEP, versus a larger decline from 89.5% to 64.6% for IMPT. Across both mild and large motion conditions, SFEP produced a higher proportion of peaks with small relative dose deviations (<10% and <20%), indicating stronger geometric and dosimetric stability. IMPT showed more peaks with severe deviations (>80%), whereas SFEP kept these occurrences minimal, demonstrating superior motion-shift robustness.Conclusion:
The SFEP framework enables motion-robust proton LATTICE planning by delivering each peak with a single optimally chosen beam angle. SFEP maintains plan quality while improving peak fidelity, spatial stability, and target coverage under range uncertainty and motion.| Mild Motion-Shifted Plans | Large Motion-Shifted Plans | |||||
| < 10% | < 20% | > 80% | < 10% | < 20% | > 80% | |
| SFEP | 42% | 66% | 2% | 37% | 60% | 6% |
| IMRT | 19% | 36% | 6% | 14% | 30% | 12% |