S1947
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Results:
objectives. The results demonstrated VMATdyn plans achieved comparable target coverage in PTV_70 and GTV of primary tumour (GTV_P). A significant reduction in the dose received by critical OIs was also observed when utilizing VMATdyn, particularly parotid glands (12.8% and 16.8% reduction in mean dose for left and right parotids, respectively). Furthermore, the VMATdyn exhibited significant improvement in target coverage in nodal GTV(GTV_N) and PTV_63 compared to VMATcon(Table 1). Conclusion: VMAT in combination of modulated ports and dynamic collimator rotation shows promise for refining treatment precision and reducing toxicity in NPC radiotherapy. Notably, the reduced dose to parotid glands may mitigate xerostomia—a common side effect—potentially improving patients' quality of life after treatment. These preliminary findings warrant validation through larger clinical trials to assess clinical applicability and long-term outcomes. Keywords: Nasopharyngeal Carcinoma, VMAT Dynamic Digital Poster 3770 Accuracy of online dose calculation on a novel type of CBCT for esophageal cancer patients Ashaya T. Jaglal 1,2 , Leigh A. P. Bruijs 1,2 , Peter S. N. van Rossum 1,2 , Elisabeth D. Geijsen 1,2 , Arjan Bel 1,2 , Jan Wiersma 1,2 , Suresh Senan 1,2 , Eva Versteijne 1,2 , Jorrit Visser 1,2 1 Radiation Oncology, Amsterdam University Medical Center, Amsterdam, Netherlands. 2 Cancer Treatment and Quality of Life, Cancer Center Amsterdam, Amsterdam, Netherlands Purpose/Objective: At our department, online adaptive radiotherapy for esophageal cancer relies on synthetic CT (sCT) images. Recent hardware and software upgrades now enable direct dose calculation on HyperSight CBCT (HS-CBCT; Varian Medical Systems, Palo Alto, CA). This study evaluated the accuracy of performing dose calculation directly on HS-CBCT images compared with reference sCT-based dose calculations. Material/Methods: Five patients enrolled in an ethics board-approved study and treated with online adaptive radiotherapy for esophageal cancer were retrospectively analysed (neoadjuvant chemoradiotherapy, 23 fractions of 1.8 Gy). Twenty-two fractions with available post- treatment, 6-second lasting, HS-CBCT imaging were studied. For each fraction, a sCT was generated using deformable registration from the planning CT, and dose calculations were performed in a simulation version of the clinical software using the identical
All VMATcon and VMATdyn plans met clinical
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