S1805
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
evaluate efficiency improvements, and propose an optimized solution for resource-limited settings. Material/Methods: Twenty-five patients with brain metastases (19 lung, 6 breast cancer; mean age 58.6±6.8 years; mean whole- brain PTV 1635±182 cc) were enrolled. Two plans were generated using uRT-TPOIS: Control: bilateral HS (4 non-coplanar arcs); Experimental: unilateral HS (1 non- coplanar arc). RTOG0933 constraints were strictly applied: hippocampal Dmax(0.03cc) ≤ 16 Gy, D100% ≤ 9 Gy, and PTV D98% ≥ 25 Gy. Treatment parameters: non-coplanar VMAT (HyperArc-like), 6MVFFF, Collapsed Cone convolution algorithm (2mm grid). Metrics included dosimetric indices (RTOG0933 compliance, CI, HI), efficiency (MU, BOT), complexity (MCS), and plan quality (PQM). Results: Dosimetric Superiority: Unilateral HS significantly improved PTV coverage (D98% 28.3±0.4 Gy vs. 27.6±0.5 Gy, +2.5%, P<0.001), with better CI (0.93±0.02 vs. 0.82±0.03) and HI (0.14±0.02 vs. 0.22±0.04). Hippocampal Dmax(0.03cc) was 13.03±0.74 Gy (bilateral: 14.06±0.82 Gy), and D100% 7.8±0.6 Gy, all meeting RTOG0933. OARs showed reduced doses: optic nerve Dmax (29.95-30.07 Gy vs. 31.80-31.90 Gy) and lens Dmax (5.80-5.94 Gy vs. 6.26-6.40 Gy).Efficiency & Complexity: Unilateral plans reduced MU by 58% (1024±68 vs. 2486±154), BOT to 312±8s (vs. 428±16s), and planning time by 62% (15±3 vs. 30±5 min). PQM improved (98.2±0.9 vs. 87.5±2.6, P<0.001) with higher MCS (0.38±0.07 vs. 0.17±0.03).Low-Dose Coverage: Unilateral HS increased hippocampal 周 边 V95% (96.7% vs. 91.3%) and dose gradient (9.2±0.8 vs. 6.1±0.9 Gy/mm). Conclusion: Unilateral HS with 1 non-coplanar arc meets RTOG0933 criteria, enhancing PTV coverage (+2.5%) and efficiency (BOT ↓ 27%). It reduces complexity (MCS ↑ 123.5%), improves low-dose conformity, and offers a cost-effective solution for resource-limited regions. Prospective studies on neurocognitive preservation are warranted. Keywords: Unilateral Hippocampal Sparing Dosimetric study of target coverage & OAR dose by combining arcs of 6MV and 15MV versus arcs of 6MV in VMAT chemoradiation of carcinoma mid- oesophagus Dhiraj Sinha 1 , Arun Raj Soman 1 , Abhijit Pal 2 , Sanjay Sankad 2 , Ashwini K 2 1 Department of Radiation Oncology, Optimus Oncology Khandesh Cancer Center, Dhule, India. 2 Department of Medical Physics, Optimus Oncology Khandesh Cancer Center, Dhule, India Digital Poster 563
Conclusion: Prediction accuracy consistently improved with increasing training set size, resulting in overall high accuracy for N=1000, with only 1 in 1200 test patients having a constraint violation. Prediction errors were still decreasing at N=1000. Further enlarging the training set size to more than 1000 patients could potentially reduce relatively large errors observed in a subset of patients. Keywords: Automated planning, dataset size, dose prediction Digital Poster 556 Dosimetric Advantages of Unilateral Hippocampal Sparing in UIH uRT-linac 506c/uRT-TPOIS Radiotherapy System: A Clinical Feasibility Study. Xiaolong Cheng 1 , Bourama SANGARE 2 , Lu Zhang 3 , Jiping Liu 1 1 Radiation Physics, Zhejiang Cancer Hospital, Hangzhou, China. 2 Radiation Oncology, Hospital in Mali, Bamako, Mali. 3 Radiation Oncology, First People's Hospital of Aksu Prefecture, Aksu, China Purpose/Objective: To address the clinical need for hippocampal sparing (HS) in whole-brain radiotherapy for multiple brain metastases, traditional bilateral HS exhibits high plan complexity and low efficiency. This study explored the feasibility of unilateral (left) HS using the domestic UIH uRT-linac 506c/uRT-TPOIS system, aiming to verify its dosimetric performance against RTOG0933 criteria,
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