S1993
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Keywords: various tumor sites, RapidArc Dynamic, RAD
objective, priorities). A MU objective was not available for RAD. For the RA plans, MU objective was set at 270 MU/Gy but relaxed if the first optimization did not give a close DVH comparison with RAD. Dose distributions were calculated with Acuros XB 18.1 and 2.5 mm grid. D98%, D50%, and D2% for PTV total (encompassing lymph node regions/LNR + SIB PTVs) were extracted, and homogeneity index (HI), V95% and V80% conformity indices (CI) were calculated. DVH’s were evaluated and organ of interest dose level selected to express organ specific change in same dose range as CI’s. Differences were calculated by subtraction for HI and CI, and by percentage calculation for organ volume. All plans were measured with a device from an independent vendor before the start of the treatment and analyzed with gamma evaluation. Results: We analyzed 20 cases (Figure 1) including 16 SIB prescriptions with PTV total dose range 42-56 Gy and SIB 51-70 Gy, and another 4 single dose prescriptions (range 36-50 Gy). RAD resulted 18% higher MU (354 MU/Gy vs. 301 MU/Gy) and on average 282 degrees reduced arc span (509 degrees/1.4 arcs vs. 791 degrees/2.2 arcs) (Figure 2). In DVH comparisons, RAD performed better than RA for HI (12/20 cases), 95% CI (17/20), 80% CI (17/20), and organ volume coverage (16/20) (Figure 1). The gamma pass rate of the measurements for all RAD plans was at least 97% for gamma criteria 2 mm/3%. Beam on time reduced with RAD by average 44 s (120 s vs. 164 s). Conclusion: The plan quality with RAD and RA was clinically comparable for various tumor sites. On average RAD enables shorter delivery times compared to RA. The clinical workflow with RAD was similar to that with RA.
Digital Poster 4331 Feasibility of Pulmonary Vein Sparing
Radiotherapy for Locally Advanced Lung Cancer Fereshteh Gholami 1 , Glenn Whitten 2 , Gerard M Walls 3,1 , Conor K McGarry 2,1 1 Johnston Cancer Research Centre, Queen’s University of Belfast, Belfast, United Kingdom. 2 Radiotherapy Physics, Northern Ireland Cancer Centre, Belfast Health and Social Care Trust, Belfast, United Kingdom. 3 Cancer Centre Belfast City Hospital, Belfast Health & Social Care Trust, Belfast, United Kingdom Purpose/Objective: Cardiac events after thoracic radiotherapy for non– small cell lung cancer (NSCLC) are a concern during survivorship. Incidental radiation dose to the pulmonary veins (PVs) has been linked to atrial fibrillation1–3. Planning strategies that prioritize substructure avoidance have shown potential to reduce cardiac and pulmonary toxicity4. This study investigates the feasibility and dosimetric effects of sparing the PVs. Material/Methods: Fifteen NSCLC patients were selected based on total PV Dmax in three categories: <10Gy (category 1), 10– 30Gy (category 2), and >50Gy (category 3) (n=5/group). All cases were re-planned in Eclipse (Varian Medical Systems, Palo Alto, USA) using the anisotropic analytical algorithm (AAA, v16.1.4), following the department’s latest volumetric modulated arc therapy (VMAT) protocol. Treatment planning (TP) typically employed two half-arcs (0–180°), with additional partial or full arcs as needed to optimize organ-of- interest (OAI) sparing.Initial optimization prioritized PTV coverage and standard OAI constraints (lungs, heart, spinal cord, and when relevant, brachial plexus, esophagus). A second plan incorporated additional objectives to spare total, left (LPV), and right (RPV) pulmonary veins. PV dosimetry focused on V10 (percentage volume receiving ≥ 10Gy) and D0.1cc (dose to the hottest 0.1cm ³ ), following published methods1– 3.Dosimetric differences between initial and PV- sparing plans were analyzed using the Wilcoxon signed-rank test. Results: Analysis focused on both categories 2 and 3 combined, since category 1 cases were already within tolerance. Compared with standard plans, PV-sparing plans showed statistically significant reductions in both D0.1cc (PVs: p = 0.002, LPV: p = 0.022) and V10 (PVs: p = 0.025, LPV: p = 0.045) across PVs and LPV, while RPV reduction was not statistically significant
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