S2047
Physics - Image acquisition and processing
ESTRO 2026
solutions for delineation only allow a limited set to be used clinically. This multi-center study is the first to identify the optimal PCCT reconstructions for delineating both target volumes (primary tumor and lymph nodes) and organs at risk (OARs) in locally advanced or metastatic lung cancer patients. Material/Methods: Data and images generated at the NAEOTOM alpha system (Siemens Healthineers, Germany) were collected for 25 patients after obtaining written informed consent. Based on a pilot at one of the institutions eleven reconstructions per patient were selected: VMIs using five energies (40, 60, 70, 100, 190 keV) and two kernels (Br40 and Bl64), plus an iodine map. A MIM Software workflow was created and subsequently followed by six radiation oncologists (3 Erasmus MC and 3 USZ). Per patient, four randomized and blinded reconstructions were initially reviewed; the least informative reconstruction was iteratively removed and replaced with a new one, until one to five most complimentary reconstructions were retained. The readers were asked to provide up to three reasons for selecting each reconstruction. Data were analyzed and histograms were created. Results: On average, 2.2 reconstructions per patient were selected, with considerable variance among readers: the average number of reconstructions per reader was 1.1, 1.5, 1.6, 2.8, 3.0 and 4.1, respectively. The two most chosen reconstructions were ‘Br40 60keV’ and ‘Bl64 70keV’. The reconstructions most frequently selected for distinguishing the primary tumor from lung tissue was a sharp kernel reconstruction (Bl64) at 70 keV, while a smooth kernel reconstruction (Br40) at 60 keV was preferred for differentiation from mediastinal structures (Figure 1 and 2). Smooth kernel reconstructions at 40, 60 and 70 keV were preferred for differentiating tissue from vessels, confirming atelectasis and delineating OARs.
Conclusion: A conventional planning CT is typically acquired at one energy setting that has a similar appearance as a 70 keV VMI. Here, the readers chose in general more than one reconstruction and these varied in energy, indicating a benefit of PCCT. While the preferred sharp kernel VMI had an energy of 70 keV, the smooth kernel VMI corresponded to a lower energy (60 keV), which enhances iodine contrast and is advantageous in the mediastinum. Keywords: Photon-counting CT; Lung cancer; Digital Poster 1008 MR-visible composite material for radiation oncology applications Astrid Hafner 1 , Markus Ortner 2 , Ivo Rausch 2 , Wolfgang Lechner 1 1 Department of Radiation Oncology, Medical University of Vienna, Vienna, Austria. 2 Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria Purpose/Objective: Solid polymers are generally not visible in MRI [1]. However, MRI-visible solid materials would be highly beneficial for radiation oncology applications, as they would allow for more accurate patient positioning, improved image registration between MRI and (CB)CT images [2] and improve brachytherapy workflows with positive contrast catheters and surface moulds [3]. Additionally, phantoms fully made of MRI-visible solid material would exhibit superior stability and would not be prone to flow artefacts [4]. In this work, we present initial results of a novel MRI-visible solid composite material that consists of paraffin oil containing microcapsules enclosed in a matrix of ultraviolet light
(UV) curable polymer. Material/Methods:
The material was prepared by encapsulating paraffin oil via a two-step double emulsion process in UV- curable resin. The resulting capsules were mixed with
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