S1756
Physics - Dose prediction/calculation, optimisation and applications for particle therapy planning
ESTRO 2026
The lancet oncology, 2016, 17(11): 1509-20. Keywords: Proton Arc Therapy Robustness
valuable insights for clinical application. Material/Methods:
A retrospective analysis was conducted on data from 20 NPC patients. Each patient's CT images included a pre-treatment CT scan (CT0) and a follow-up CT scan (CT1) acquired 25 days after the initial CT0 scan. A total of three plan sets were designed, as below: (a) robustly optimized plans for PAT (PAT0) and IMRT (IMPT0) were generated on the CT0 dataset, accounting for a 3 mm patient positioning and 3% range uncertainty, resulting in 21 error scenarios; (b) following the deformable image registration between CT1 and CT0, the PAT0 and IMPT0 plans were transferred to the CT1 dataset for dose recalculation without re-optimization, resulting in the PAT0-1 and IMPT0-1 plans, respectively; (c) subsequently, new robustly optimized PAT (PAT1) and IMPT (IMPT1) plans were generated separately on the CT1 dataset. Dosimetric comparisons between PAT0 and IMPT0, PAT0-1 and PAT1, as well as IMPT0-1 and IMPT1, were performed for both target coverage and organ-at-risk (OAR) sparing using dose-volume histogram (DVH) parameters. Results: For the target, PAT0-1 was superior to IMPT0-1. Additionally, PAT1 was superior to PAT0-1, as was IMPT1 to IMPT0-1. For the OARs, the mean deviation of Dmax and D1cc to the spinal cord , V30 and Dmean to the larynx and oral cavity, and Dmean to the parotid are lower for PAT0-1 plan compared with IMPT0-1 plans plan (p<0.05);V30 and Dmean to the larynx and parotid are lower for PAT1 plan compared with PAT0-1 plans plan (p<0.05); Dmean to the left parotid, V30 and Dmean to the right parotid are lower for IMPT1 plan compared with IMPT0-1 plans plan (p<0.05). Conclusion: PAT offers superior robustness to anatomical changes and enhanced OARs sparing compared to IMPT in NPC radiotherapy. Nevertheless, deficiencies in target coverage persist due to concurrent range and patient positioning uncertainties. The introduction of online/offline adaptive approaches or shortened reassessment intervals is advised to optimize plan modifications, ultimately improving therapeutic outcomes and safety. References: HAN B, ZHENG R, ZENG H, et al. Cancer incidence and mortality in China, 2022 [J]. Journal of the National Cancer Center, 2024, 4(1): 47-53. ZHANG Y, CHEN L, HU G-Q, et al. Gemcitabine and cisplatin induction chemotherapy in nasopharyngeal carcinoma [J]. New England Journal of Medicine, 2019, 381(12): 1124- 35.SUN Y, LI W-F, CHEN N-Y, et al. Induction chemotherapy plus concurrent chemoradiotherapy versus concurrent chemoradiotherapy alone in locoregionally advanced nasopharyngeal carcinoma: a phase 3, multicentre, randomised controlled trial [J].
Digital Poster Highlight 3694 Proton arc therapy linear-energy-transfer optimization for stereotactic radiosurgery using an alternating direction method of multipliers Yuanyuan Ma 1,2 , Runqiu LI 1 , Yongrui Zhao 2 , Manju Liu 3 , Lewei Zhao 4 1 Medical Physics, Duke Kunshan University, Kunshan, China. 2 Department of Radiation Oncology, Xuanwu Hospital, Capital Medical University, Beijing, China. 3 Medical Physics, Duke Kunshan University, Suzhou, China. 4 Department of Radiation Medicine, MedStar Georgetown University Hospital, Washington, DC, USA Purpose/Objective: This study investigates the feasibility and potential clinical benefits of a novel linear energy transfer (LET) optimization method for proton arc therapy (PAT) in stereotactic radiosurgery (SRS) for small-volume brain metastases. The method incorporates a minimum monitor unit constraint and employs the alternating direction method of multipliers (ADMM) for optimization. Material/Methods: PAT plans were developed for small-volume brain metastases (lesion diameter ≤ 3 cm, volume ≤ 6 cm ³ ) using a MATLAB-based ADMM framework for plan optimization. PAT plan is created by a 360 degree full arc with 15 degree beam angle field frequency. The approach integrates LET optimization into PAT optimization. In the ADMM-LET framework, the optimization process entails iteratively solving the dose sub-problem and the LET sub-problem, simultaneously ensuring compliance with the MMU constraint. The weight of the dose objective and LET objectives are tuned. A dual-target small-volume brain metastases clinical case was selected to demonstrate
the feasibility of the method. Multiple beam configurations were evaluated to assess the
advantages of LET-optimized PAT over multi-beam intensity-modulated proton therapy (IMPT) on both tumor coverage and organ-at-risk (OAR) sparing. Results: LET-optimized PAT plans were compared with the non- LET-optimized plans. For GTV1, the maximum, minimum, and mean LET increased by 4.92, 2.22, and 3.62 keV/ μ m, respectively. For GTV2, corresponding increases were 4.24, 1.35 and 3.03 keV/ μ m. In contrast, high-LET exposure to adjacent OARs was reduced. Specifically, the left inner ear showed reductions in maximum, minimum and mean LET by 1.96, 0.24 and 0.97 keV/ μ m. The brainstem exhibited a reduction in maximum LET by 0.90 keV/ μ m and mean
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