S1908
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
rotation and incorporates integrated Static Angle Modulated Ports (STAMPS) within volumetric modulated arc therapy (VMAT) (Populaire et al, 2025). The aim of this study is to evaluate the dosimetric plan quality, optimization efficiency, and delivery time of RAD compared to conventional VMAT for stereotactic ablative body radiotherapy (SABR) of the pancreas, Pancreas SABR VMAT treatment planning is performed using a standard objective template in order to meet clinical guidelines for PTV25Gy, PTV33Gy and PTV36Gy. Ten CT datasets of previously treated patients were chosen for this study. The VMAT optimization objectives were applied to RAD plans. RAD-specific parameters, including STAMP weighting and iteration number, were systematically evaluated. Two using a simultaneously integrated boost (SIB) prescription of 36Gy delivered in 5 fractions. Material/Methods: techniques were compared: RAD1, a single arc with one STAMP at 220° using an arc-dominant method and optimized collimator; and RAD2, two arcs with five STAMPs at 125°, 135°, 210°, 225°, and 235° using a balanced method and optimized collimator.Optimization time, number of optimizations to final plan, delivery time and dosimetric plan quality were compared. Additionally, the optimal RAD plan and the original VMAT plan for each patient were independently reviewed in a blinded assessment by a Radiation Oncologist. Results: The optimal RAD plan for all 10 patients was the RAD1 technique plan for dosimetry, optimization time and delivery time. The median time to optimize are 364s for VMAT, 139s for RAD2 and 78s for RAD1 respectively. Median beam on time for the VMAT plans is 172s. This is reduced to 72s for the RAD1 technique.The median % difference in PTV coverage between RAD1 and VMAT for PTV25Gy D99.9(Gy) is 5.4%, PTV33Gy D99.9(Gy) is 0.4%, PTV36Gy D99.9(Gy) is 0.7% and PTV Dmax (Gy) is -1.1%. The critical organs of interest are Duodenum, Small Bowel and Stomach. The dose guidance for these structures is V20Gy < 20cc. This was achieved using both planning strategies for all plans.The Radiation Oncologist preferred 7 RAD1, 2 VMAT and had no preferred technique for 1 dataset during the blinded assessment. Conclusion: RAD with 1 Arc, 1 STAMP offers faster optimization and treatment times while maintaining or improving plan quality compared to VMAT. The use of RAD could potentially lead to dose escalation up to 50Gy for Pancreas SABR. References: Populaire P, Defraene G, Aerts K, Reynders T, Piot W, Vanstraelen B, Haustermans K, Crijns W. Rotational arc treatments with static ports and dynamic collimation reduces cardiopulmonary dose for esophageal cancer
110 s (21 s shorter than VMAT) was achieved with the two arc RAD plans with three STAMPs using balanced or static setting. The longest median beam on time of 146 s (15 s longer than VMAT) was measured on a two arc RAD plan with 5 STAMPs on the static dominant setting. Compared to VMAT the median increase in monitor units was between 22.6 % and 47.8 %. In terms of organ-at-risk sparing, mean ipsilateral lung doses increased 0.4-0.9 Gy by median in the RAD plans. However, significant decreases of 0.2 Gy and 0.8-2.1 Gy in mean doses of contralateral lung and breast, respectively, were seen in the RAD plans compared to the VMAT plans. The difference in mean heart dose was 0.1-0.2 Gy between RAD and VMAT.
Conclusion: RapidArc Dynamic can decrease beam on times of breast treatments. The mean heart and contralateral breast doses were more effectively spared with RAD while ipsilateral lung doses increased slightly. References: [1] Boman E, Rossi M, Haltamo M, Skyttä T, Kapanen M. A new split arc VMAT technique for lymph node positive breast cancer. Phys Med 2016;32:1428–36. https://doi.org/10.1016/j.ejmp.2016.10.012.[2] Rossi M, Boman E, Kapanen M. Contralateral tissue sparing in lymph node-positive breast cancer radiotherapy with VMAT technique. Med Dosim 2019;44:117–21. https://doi.org/10.1016/j.meddos.2018.03.005. Keywords: Breast cancer, VMAT, treatment planning Advancing Pancreas SABR: Dosimetric and Efficiency Comparison of RapidArc Dynamic vs Standard VMAT Darina Hickey, Cora Marshall, Alina Mihai, Luke Rock Radiotherapy Department, Beacon Hospital, Dublin, Ireland Purpose/Objective: RapidArc Dynamic (RAD) is a novel optimization and delivery system that enables dynamic collimator Digital Poster 2946
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