S2490
Physics - Radiomics, functional and biological imaging, and outcome prediction
ESTRO 2026
contrast dynamics, hindering its use for functional imaging. However, enhanced image quality and rapid scan times of imaging solution HyperSight equipped onto radiation machines (Halcyon or TrueBeam) offer a solution for DCE-CBCT. This approach provides the potential for CBCT-based functional measurements during adaptive radiotherapy. Material/Methods: A contrast enhanced calibration CT (CECT) phantom, containing capsules of varying diameter and orientation mimicking iodine contrast enhancement, was used to characterize image quality metrics, partial volume effects and spatial resolution on four modalities: Canon CTSim scanner, Halcyon (HyperSight CBCT), TrueBeam (HyperSight CBCT), and TrueBeam (CBCT).1 For a capsule of the same diameter and orientation, HU consistency was measured as the variation in mean CT number across variable mAs (50, 100, 150, 200, 250, 300) while HU uniformity was measured as the variation in CT number, voxel-wise, at approximately 300 mAs. This was compared with the Gammex-RMI model 467 phantom, containing uniform capsules mimicking clinically relevant tissues, used for CT quality assurance.2 Spatial resolution was characterized by directionally-dependent 10% modulation transfer function (MTF) calculations across variable reconstruction parameters. Results: The measured volumes (10 mm 1.56 g/cc capsules) in the CECT phantom varied by less than 0.5% for CT, 1% for HyperSight (TrueBeam), 2% for HyperSight (Halcyon), and 5% for CBCT, across mAs settings. At 300 mAs, they had a maximum coefficient of variation of 11% for CT and HyperSight (TrueBeam), 13% for HyperSight (Halcyon), and 12% for CBCT. Averaged over all orientations, they varied from ground truth by less than 0.3% for CT, 0.9% for HyperSight (TrueBeam), 3% for HyperSight (Halcyon), and 20% for CBCT.1 The measured volume (1.82 g/cc capsule) in the Gammex- RMI phantom varied by less than 1.5% across mAs settings, with a 12% coefficient of variation at 300 mAs for CT. The partial volume effect contributed to a decrease in contrast enhancement. MTF calculations were decreased for CBCT as compared with HyperSight CBCT.
Conclusion: Static acquisition with the CECT phantom displayed improved image quality for HyperSight CBCT through greater HU consistency, lesser pronounced partial volume effects, and greater spatial resolution compared to standard CBCT, demonstrating its potential for assessment of contrast enhancement. Future work will focus on motion artifacts and temporal resolution through dynamic acquisitions. References: 1 Coolens C, Mohseni H, Dhodi S, Ma S, Keller H, Jaffray DA. Quantification accuracy for dynamic contrast enhanced (DCE) CT imaging: phantom and quality assurance framework. European Journal of Radiology. 2018;106:192-198. doi:https://doi.org/10.1016/j.ejrad.2018.08.0032 Tissue Characterization Phantom Model 467 User’s Guide, cspmedical.com/content/102- 1492_tissue_phantom_user_guide.pdf. Accessed 11 Nov. 2025. Keywords: Perfusion, quantitative imaging, DCE-CT A Quantitative Susceptibility–Based Framework for Cerebral Metabolic Rate of O ₂ and pO2 Estimation: validation with Digital and Realistic MRI Phantoms Paolo Fenech, Chiara Tinelli, Giovanni Parrella, Guido Baroni, Chiara Paganelli DEIB, Politecnico di Milano, Milano, Italy Purpose/Objective: Tissue oxygenation strongly influences radiotherapy response. Quantitative susceptibility mapping (QSM) combined with cerebral blood flow (CBF) enables estimation of the cerebral metabolic rate of oxygen (CMRO ₂ ), providing a potential biomarker for local hypoxia. Based on the QSM-CBF framework of Zhang et al [1], this study employs a Tikhonov-regularized quadratic programming approach for stable and clinically feasible estimation of CMRO2 and pO ₂ . Validation was conducted using (i) an extended XCAT- derived digital phantom to assess algorithmic consistency and (ii) an open-source QSM phantom to evaluate clinical translation in radiotherapy. Digital Poster 4695
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