ESTRO 2025 - Abstract Book

S3071

Physics - Image acquisition and processing

ESTRO 2025

The standard sagittal plan captured the full tumour motion in all patients. The contrast was better in the 10 mm plane for small tumours. Patients were generally on the scanner couch for around 40 min.

Conclusion: A thin plane of 2D-cine MRI (10 mm) provides good contrast, especially for very small tumours, and can capture the full tumour motion. In the main trial cohort, a total of 6 min of this image series will be acquired to generate comprehensive tumour motion data. Patients with reduced physical performance may not tolerate the MRI examination.

Keywords: SBRT, 2D-cine MRI, Tumour respiratory motion

References: 1. Nielsen, T.B., et al., Impact of 4D image quality on the accuracy of target definition. Australas Phys Eng Sci Med, 2016. 39(1): p. 103-12. 2. Wikström KA, Isacsson UM, Pinto MC, Nilsson KM, Ahnesjö A. Evaluation of irregular breathing effects on internal target volume definition for lung cancer radiotherapy. Med Phys. 2021 May;48(5):2136-2144.

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Digital Poster Technical and clinical feasibility assessment of photon-counting CT in radiotherapy Patrick Wohlfahrt 1 , Matthias Baer-Beck 2 , Jannis Dickmann 1 , Martina Mortsiefer 1 , Stefanie Aratsch 3 , Ina Reher 4 , Thomas Schwarz 3 , Jainil Shah 5 1 Varian, Cancer Therapy Imaging, Siemens Healthineers, Forchheim, Germany. 2 Diagnostic Imaging, Computed Tomography, Siemens Healthineers, Forchheim, Germany. 3 Customer Services, Cancer Therapy Imaging, Siemens Healthineers, Forchheim, Germany. 4 Customer Services, Siemens Healthineers, Hamburg, Germany. 5 Varian, Cancer Therapy Imaging, Siemens Healthineers, Cary, NC, USA Purpose/Objective: Photon-counting CT (PCCT) with its ability to provide high-resolution, high-contrast and material-parameter images in a single acquisition was proven to add value in diagnostic radiology [1]. Its translation into radiotherapy workflows was investigated in this clinical and technical feasibility study. Material/Methods: Radiotherapy PCCT scan protocols were optimized by clinically trained staff based on more than 250 oncological patient cases acquired on NAEOTOM Alpha (Siemens Healthineers). For photon and proton dose calculation, the accuracy of direct PCCT-based prediction of relative electron density (RED) and proton stopping-power ratio (SPR) was assessed with the Advanced Electron Density Phantom (Sun Nuclear) in head and body setup. The performance of extended field-of-view reconstructions (conventional and with support of artificial intelligence, AI) for collision indication was evaluated using an anthropomorphic thorax-abdomen phantom (Universal Medical). The performance of respiratory 4D CT in sequential and spiral mode for motion management was assessed using the Dynamic Thorax Phantom (Sun Nuclear) for regular breathing patterns. Results: Different radiotherapy requirements on image quality depending on clinical task are best addressed by combining various PCCT-derived image representations (Figure 1). This includes full field-of-view RED/SPR reconstruction for radiotherapy planning; and multiple anatomically trimmed field-of-view reconstructions for tumor segmentation, i.e. high-contrast (low-energy virtual monoenergetic image with smooth edge-enhanced soft-tissue impression), complementary high-resolution (high-energy virtual monoenergetic image with sharp edge-enhanced bone/lung impression) and iodine-enhancement images (for contrast-enhanced PCCT only). PCCT-derived RED and SPR