S561
Clinical – Head & neck
ESTRO 2026
Brezae 5,6 , Adam Burr 7 , Francesca Caparrotti 8 , Alexey Cherchik 4 , Sarah Deschuymer 9 , Mélanie Doré 10 , Fréderic Duprez 9,11 , Vincent Gregoire 5 , Martin de Jong 12 , Rasmus Kjeldsen 3 , Michiel Kroesen 13,14 , Haitam Lamtai 15 , Martin Langé 10 , Mauro Loi 16 , Séverine Radacot 5 , Anne-Agathe Serre 5 , Roger Sun 1,2 , Vicki Trier Taasti 17 , Patrick Wohlfahrt 18 , Charlotte Robert 1,2 1 Université Paris-Saclay, Gustave Roussy, Inserm, Molecular Radiotherapy and Therapeutic Innovation, U1030, 94800, Villejuif, France. 2 Department of Radiation Oncology, Gustave Roussy Cancer Campus, Villejuif, France. 3 Department of Oncology, Aalborg University Hospital, Aalborg, Denmark. 4 Center for Proton Therapy (CPT), Paul Scherrer Institute (PSI), Villigen, Switzerland. 5 Centre Léon Bérard, Department of Radiation Oncology, Lyon, France. 6 Claude Bernard University, -, Lyon, France. 7 Department of Human Oncology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA. 8 Radiation Oncology Department, Clinique Générale Beaulieu - Swiss Medical Network, Geneva, Switzerland. 9 Ghent University Hospital, Department Radiation Oncology, Ghent, Belgium. 10 Department of Radiation Oncology, Institut de Cancérologie de l'Ouest, Saint Herblain, France. 11 Faculty of Medicine and Health Sciences, Dept of Human Structure and Repair, Ghent University, Ghent, Belgium. 12 Department of Radiation Oncology, Leiden University Medical Center, Leiden, Netherlands. 13 HollandPTC, -, Delft, Netherlands. 14 Department of Radiation Oncology, Erasmus MC
Premier 3T, GE Healthcare). To identify DECT-derived virtual monoenergetic images (VMIs) with optimal tumour contrast, the image impression of VMIs at energies of [40,45,50,55,60,65,100,190] keV were rated (±3) with respect to VMI at 70keV, 120kVp SECT- equivalent (Figure 1A). The gross target volume (GTV) was delineated in three rounds (four weeks apart) based on SECT+MRI (conventional), DECT+MRI, or DECT only (Figure 1B). Clinical reports of patient’s endoscopy, MRI and PET, together with an isotropic 7cm bounding box centred around the tumour were supplemented for target delineation. Delineation timings were recorded to evaluate workflow impacts. The GTV variability in size and spatial distribution was assessed.
Cancer Institute, Rotterdam, Netherlands. 15 Department of Radiotherapy and Radiation
Oncology, University Hospital Würzburg, Würzburg, Germany. 16 Department of Radiotherapy, Careggi University Hospital, Florence, Italy. 17 Danish Centre for Particle Therapy, Aarhus University Hospital, Aarhus, Denmark. 18 Siemens Healthineers, Varian Cancer Therapy Imaging, Forchheim, Germany Purpose/Objective: Target delineation is subject to high intra- and inter- observer variability arising from the limited contrast of conventional 120kVp single-energy CT (SECT) commonly acquired in radiotherapy. To enhance tissue contrast and improve delineation accuracy and consistency, dual-energy CT (DECT) enables reconstructions of various image types. This proof-of- concept multi-centre study aims at optimising DECT- based workflows for target delineation and serving as foundation for a larger-scale investigation. Material/Methods: Nineteen radiation oncologists from eleven centres evaluated three patients with unresected head-and- neck tumours (2 oropharynx, 1 larynx) receiving contrast-enhanced TwinSpiral DECT (SOMATOM Go.Sim, Siemens Healthineers) and MRI (SIGNA
Results: The visual image quality ratings revealed VMI at 50keV as the preferred DECT image for delineation with clearly improved contrast perception (median rating ± standard deviation per patient: 2.0±1.0, 2.0±0.6, 1.5±1.3). The increased tissue contrast provided by DECT compared to SECT highlighted the need for optimising window-level settings for target delineation, tended to reduce delineation timings (median decrease of 2:15min), and increased the confidence in using CT as main modality for target delineation (i.e. avoiding MRI). Figure 2A illustrates the inter-observer variability in GTV delineated on DECT+MRI (providing the highest contrast) as a color-coded heatmap for contour agreement between radiation oncologists. Independent of the delineation rounds, the GTV
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