S2019
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Elementplanner has to add the fields manually and select the optimum arc configurations and best couch angles to be used for the plans. According to that the total plan time for hyperarc around 45 minutes however, the total plan time for element plans 120 minutes on average. All OAR dose constraints, as per the 2022 UK-SABR consensus guidelines, were met; however, GK and HyperArc plans exhibited improved OAR sparing compared to Elements plans with 5 mm MLC. Conclusion: Despite the high Dmax in GTC, GammaKnife remains the optimal platform for vestibular schwannoma SRS, offering superior dose gradient and OAR sparing. For linac-based SRS, the HyperArc technique with a 2.5 mm MLC provides dosimetric advantages over 5 mm MLC-based planning. These findings support the continued use of GK for high-precision SRS while highlighting HyperArc as a viable alternative for institutions utilizing linac-based delivery. References: Tamura M, et al.Hearing preservation after Gamma Knife radiosurgery for vestibular schwannomas.J Neurosurg.2009;111(4):845-854.Yang I, et al.Hearing preservation after stereotactic radiosurgery for vestibular schwannoma: a systematic review.J Clin Neurosci.2009;16(6):742-747.Paddick I, Lippitz B.A simple dose gradient measurement tool to complement the conformity index.J Neurosurg.2006;105:194-201.Sahgal A, et al.Stereotactic radiosurgery for vestibular schwannoma: International Stereotactic Radiosurgery Society (ISRS) guidelines.IJROBP.2021;110(3):718- 730.UK SABR Consortium.Guidelines for Stereotactic Ablative Radiotherapy (SABR).2022. Keywords: Vestibular Schwannoma - SRS - Radiosurgery Digital Poster 5024 When planning meets reality: Evaluating Surface Dose Accuracy with FFF Beams on Halcyon khedija Ben Zid 1 , Cyrine Mokrani 1 , Eya Azzabi 1 , Montassar Razgui 2 , Lotfi Ben Sallem 2 , Najla Attia 1 , Alia Mousli 1 , Rim Abidi 1 , Chiraz Nasr 1 1 Radiotherapy, Salah Azaiz Institute, Tunis, Tunisia. 2 Medical Physics, Salah Azaiz Institute, Tunis, Tunisia Purpose/Objective: Accurate estimation of surface dose is crucial in radiotherapy, especially for head-and-neck cancer patients. The use of flattening filter free (FFF) beams may alter surface dose distribution, as the removal of the flattening filter increases the dose rate while reducing scatter and leakage radiation. This study aimed to assess the accuracy of the Eclipse treatment
improvements: (1) integration of MR-informed urethral contours into the planning workflow, and (2) vendor model updates explicitly optimizing urethral constraints. With implementation and deliverability testing, these results establish clinical viability across dose regimens, circumventing the resource-intensive need for institution-specific models. Digital Poster 5008 Comparative Dosimetric Analysis of Gamma Knife versus Linac-Based SRS for Vestibular Schwannoma: A Multi-Platform Study Mahmoud Younes, Abdul Hussein Mroue GenesisCare UK, Cromwell centre, London, United Kingdom
Purpose/Objective: This study aims to compare the dosimetric
performance and efficiency of three stereotactic radiosurgery (SRS) delivery systems: the Leksell Gamma Knife (GK), BrainLab Elements with Elekta Agility (5 mm MLC), and HyperArc on Varian Edge (2.5 mm MLC-HD). Specifically, we evaluate dose fall-off characteristics using gradient and Paddick indices, target coverage, and organ-at-risk (OAR) sparing. Additionally, we assess planning times between Eclipse and Elements planning systems. Material/Methods: Ten vestibular schwannoma patients are planned retrospectively using three stereotactic radiosurgery (SRS) platforms : the Leksell GammaKnife (Elekta), BrainLab Elements with Elekta (5 mm MLC, 6MV-FFF), and HyperArc workflow on Eclipse with Varian Edge (2.5 mm MLC-HD, 6MV-FFF). GammaKnife (GK) plans were optimized on GTV without additional margins, with the dose prescribed to the 50% isodose line. For linac-based SRS (Varian Edge and Elekta Versa), a 1- mm planning target volume (PTV) margin was applied to GTV, with all plans optimized to achieve 99% PTV coverage by 100% of the prescribed dose. Plan quality was assessed using the Paddick conformity index (PCI) and gradient index (GI), along with organ-at-risk dosimetry for the cochlea_PRV, brainstem_PRV, and Brain-GTV. Results: GammaKnife demonstrated superior dose fall-off, with a mean gradient index (GI) of 5.3 ± 0.6, compared to 5.6 ± 0.5 for the Edge (2.5 mm MLC) and 5.8 ± 0.8 for the Versa (5 mm MLC) linac-based plans. Optimization times varied significantly, with HyperArc plans (Acuros algorithm) averaging 40 minutes, while Elements plans (Monte-Carlo algorithm) required approximately 60 minutes. Hyperarc plans are created using the workflow provided on Eclipse, where the fields are added automatically, however the plans created on
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