S1836
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
first, and the final objective template from the VMAT plan was then applied to generate the RAD plan. If constraints were unmet in RAD plan, one additional optimization was performed. Optimization time was defined as a single cycle from the start of optimization to the completion of dose calculation. Scripting was used to calculate estimated delivery time. Plan metrics were compared using the Wilcoxon-signed rank test. Statistical significance was set at 0.05. Results: Compared to conventional VMAT, RAD reduced the dose to the larynx (median Dmean [Gy], 27.01 vs. 25.06, p=0.006) and oral cavity (Dmean [Gy], 40.39 vs. 38.05, p=0.002) in all cases while maintaining the target dose (PTV63 D50% [Gy], 63.12 vs. 63.05, p = 0.41; PTV56 D50% [Gy] 56.10 vs. 56.11, p=0.11) (Table 1). All high-priority constraints were satisfied; however, low-priority constraints were not achieved for one patient in both VMAT and RAD plans. Both optimization time (4.0 vs. 2.5 min, p=0.002) and delivery time (3.4 vs. 2.9 min, p=0.002) were significantly shorten for the RAD plan. MU was significantly higher in RAD plan (497.0 vs. 796.3, p=0.002).
improved target visualization—such as MR-guided radiotherapy—to enhance accuracy and reduce toxicity. References: 1- Rahib L et al., Factors Driving Pancreatic Cancer Survival Rates. Pancreas. (2025); 54(6): e530-e536. doi: 10.1097/MPA.0000000000002489.2- Bouchart et al., Preoperative treatment with mFOLFIRINOX or Gemcitabine/Nab-paclitaxel +/- isotoxic high-dose stereotactic body Radiation Therapy (iHD-SBRT) for borderline resectable pancreatic adenocarcinoma (the STEREOPAC trial): study protocol for a randomised comparative multicenter phase II trial BMC Cancer. 2023 Sep 21;23(1):891. doi: 10.1186/s12885-023- 11327-x. Keywords: Pancreatic cancer, GI toxicity, Dose accumulation Potential Utility of VMAT with Dynamic Collimator Rotation and Static Angle Modulated Ports for Nasopharyngeal Cancer Takahiro Iwai 1 , Shinya Hiraoka 1 , Hideaki Hirashima 1 , Mitsuhiro Nakamura 2 , Ryota Nakashima 1 , Takashi Mizowaki 1 1 Radiation Oncology and Image-Applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto, Japan. 2 Advanced Medical Physics, Graduate School of Medicine, Kyoto University, Kyoto, Japan Purpose/Objective: RapidArc Dynamic (RAD) (Varian Medical Systems, Palo Alto, USA) is a novel solution that enables static angle modulated ports (STAMPs) and dynamic collimator rotation.[1, 2] The purpose of this study was to evaluate the utility of RAD for nasopharyngeal cancer (NPC) compared with conventional VMAT. Material/Methods: Ten NPC patients who underwent chemoradiotherapy were included. We newly generated a conventional VMAT and RAD plan for each patient using Eclipse v18.1 (Varian Medical Systems) and compared for plan and dose metrics, optimization time, estimated delivery time, and MU. VMAT plan was created with 3 arcs (collimator angle: 30°, 330°, and 90°), fully Digital Poster 1489 covering target volume using jaw tracking system. RAD plan was created with 2 arcs, each with 4 STAMPs, and the collimator rotation was manually and automatically set for each arc. Prescribed dose was D95% = 70 Gy for PTV70, D50% ≈ 63 Gy for PTV63, and D50% ≈ 56 Gy for PTV56. Dose constraints were classified as either high- or low-priority. Optimization was repeated until all high-priority objectives were achieved, and up to three iterations were allowed for low-priority objectives. The VMAT plan was optimized
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