S2096
Physics - Image acquisition and processing
ESTRO 2026
principal stretch ≈ 9.89 %), reflecting its high compliance and mobility, although its absolute displacement magnitude remained small due to its compact size. The colon, bowel and bladder showed intermediate deformation, primarily along the inferior- superior and anterior-posterior axes. The bladder displayed moderate downward displacement with elongation, whereas the muscles remained largely stable, with minimal strain energy [Fig. 1]. Across all organs, Jacobian determinants were close to unity, indicating predominantly volume-preserving elastic deformation. Representative visualizations are provided in [Fig. 2]. Conclusion: Upright posture induces heterogeneous, organ- specific pelvic soft-tissue deformation consistent with gravitational loading. Using rigid and deformable registration, we quantified these posture-dependent biomechanical effects with high anatomical accuracy. Distinct deformation patterns were observed across organs, with the prostate and bowel showing the greatest strain responses.Incorporating posture-aware deformation modeling into treatment planning could improve target localization, dose accuracy, and adaptive workflow robustness in upright radiotherapy. These results emphasize the clinical importance of integrating gravity-informed tissue mechanics into planning systems to ensure geometric and dosimetric precision for pelvic treatments in the upright position.
References: [1] Volz L, Korte J, Martire MC, et al. Opportunities and challenges of upright patient positioning in radiotherapy. Phys Med Biol. 2024;69(18):18TR02. doi:10.1088/1361-6560/ad70ee Keywords: 3D image registration, Upright radiotherapy Digital Poster 4787 Extended Field of View (eFoV) Image Quality Analysis for Proton Therapy Using Philips Spectral CT7500 scanner Savanna K. W. Chung, Xu Zhao, Callum Gillies Radiotherapy (Proton Beam Therapy), University College London, London, United Kingdom Purpose/Objective: Proton therapy relies on CT images to provide anatomical accuracy and HU consistency, ensuring contour and dose-delivery precision. The Philips Spectral CT7500 scanner produces images using an Iterative Model Reconstruction (IMR) [1] which can then be used for treatment planning using an appropriate HU to relative stopping power calibration curve. IMR images demonstrate superior low-contrast detectability, spatial resolution, and noise reduction. However, its reconstruction diameter is restricted to 500 mm, which is insufficient for patients with high BMI or decentred setups. iDose-based eFoV reconstruction is available, with reconstruction diameters from 600 mm to 800 mm.This work focuses on evaluating image quality at the centre and at the edge of the eFoV using CatPhan504. Material/Methods: Phantom at isocentreA CatPhan504 phantom [2] was scanned centrally with standard FoV using abdomen, H+N, pelvis and thorax protocols due to their eFoV clinical relevance. A pair of IMR and iDose images was measured per protocol, followed by eFoV reconstruction for diameters of 600 mm, 650 mm, 700
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