S2078
Physics - Image acquisition and processing
ESTRO 2026
Material/Methods: In June 2025 a PCD-CT single-energy system (NAEOTOM Alpha.Prime, Siemens Healthineers, Forchheim, Germany) was installed at University Hospital Zurich available for both Radiology and Radiotherapy departments. Such a system provides integrated images (T3D, same signal processing as for standard, EI-CT), but also allows spectral post- processing. In this second case, images can be reconstructed as relative electron/mass density (ED), which can be used for dose calculations in the treatment planning systems. We commissioned the machine according to international recommendations (ImPACT acceptance testing [1], Kearns and McJury 2007 [2], and AAPM-TG66 report [3]), comparing the performance to our current CT scanner (SOMATOM Definition AS, Siemens Healthineers). We scanned the CIRS 062 electron density phantom to evaluate the reconstructed mass density values against the nominal values for different protocols, testing a difference in kV source and slice thickness. Since 07/2025 we started scanning patients with the system. For 15 patients, chosen among the first scanned for different anatomical regions, planned on the T3D images (22 plans), we recalculated the dose on ED post-processing of the same patient scan, and compared dosimetric parameters for PTV and OARs. Results: Image quality for integrated images is comparable to the EI-CT currently in clinical use. The spectral post processing provides excellent images, whose reconstructed mass density agrees with the nominal values for the phantom inserts within 1% for soft- tissue, 5% for bone, and 7% (0.014 in absolute values) for lung inserts (Figure 1). Dose calculations, performed on T3D or ED post-processing, generally agree within 1%; larger deviations occur in locations within the bones (due to the different scatter correction between T3D and ED images), or in presence of contrast (ED images suppress contrast, that instead must be overridden for T3D images).
Conclusion: Gamma-based metrics effectively identify substantial reconstruction differences in 4DCT and can be used to flag cases for manual review, contributing to time- efficient evaluation. ZeeFree reconstructions show improved anatomical accuracy in flagged cases, confirming its clinical value in respiratory-motion imaging. References: 1. Moser LJ, Mergen V, Allmendinger T, Manka R, Eberhard M, Alkadhi H. A Novel Reconstruction Technique to Reduce Stair-Step Artifacts in Sequential Mode Coronary CT Angiography. Invest Radiol [Internet]. 2024 Jan 30 [cited 2024 July 2]; Available from: https://journals.lww.com/10.1097/RLI.0000000000001 0662. Werner R, Sentker T, Madesta F, Gauer T, Hofmann C. Intelligent 4D CT sequence scanning (i4DCT): Concept and performance evaluation. Medical Physics. 2019 Aug;46(8):3462–74. 3. Jakob Wasserthal. Dataset with segmentations of 117 important anatomical structures in 1228 CT images [Internet]. Zenodo; 2023 [cited 2025 Sept 18]. Available from: https://zenodo.org/doi/10.5281/zenodo.6802613 Keywords: Artifact, Motion, Anatomical acurracy Photon counting detector computed tomography in radiotherapy: scanner commissioning and first clinical experience Serena Psoroulas 1 , Matteo Bagnalasta 1 , Crystal Sulaiman 1 , Karen Villaquiran 1 , Lotte Wilke 1 , Patrick Wohlfahrt 2 , Filipa Branco Venancio Heinitz 1 , Silvia Fabiano 1 , Michael Iff 1 , Michele Keane 1 , Klara Kefer 1 , Filipe Pires 1 , Izabela Pytko 1 , Hatem Alkadhi 3 , Thomas Frauenfelder 3 , Matthias Guckenberger 1 , Panagiotis Balermpas 1 , Stephanie Tanadini-Lang 1 1 Radiation Oncology, University Hospital Zurich, Zurich, Switzerland. 2 Cancer Therapy Imaging, Siemens Healthineers, Forchheim, Germany. 3 Diagnostic and Interventional Radiology, University Hospital Zurich, Zurich, Switzerland Purpose/Objective: Photon counting detector CT (PCD-CT) is an innovative imaging modality providing high-quality images, improved soft-tissue contrast and artefact reduction, compared to state-of-the-art energy-integrating (EI-CT) or dual-energy CT. Since 2025, it is also available for use in radiotherapy. We are reporting the results from the commissioning and the first patients treated at our department, scanned with photon-counting technology as part of their routine radiotherapy workflow. Poster Discussion 3714
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