S2389
Physics - Quality assurance and auditing
ESTRO 2026
7 Molecular Imaging-Radiotherapy and Oncology (MIRO), Université Catholique de Louvain, Brussels, Belgium. 8 Radiation Oncology, CHU Liège, Liège, Belgium. 9 Radiation Oncology, AZ Groeninge, Kortrijk, Belgium. 10 Radiation Oncology, CHIREC Delta, Brussels, Belgium. 11 Radiation Oncology, Centre Hospitalier Jolimont, La Louvière, Belgium. 12 Radiation Oncology, Ghent University Hospital, Ghent, Belgium. 13 Human Structure and Repair, Ghent University, Ghent, Belgium. 14 Radiation Oncology, Universitair Ziekenhuis Brussel, Brussels, Belgium. 15 Radiation Oncology, CHU UCL Namur, site Sainte Elisabeth, Namur, Belgium. 16 16 Nuclear medicine Imaging and Therapy Department, HUB Institut Jules Bordet, Brussels, Belgium. 17 Radiology, HUB Institut Jules Bordet, Brussels, Belgium. 18 Digestive Oncology, HUB Institut Jules Bordet, Brussels, Belgium Purpose/Objective: The ongoing STEREOPAC trial (NCT05083247) investigates whether adding isotoxic high-dose stereotactic body radiotherapy (iHD-SBRT) to neoadjuvant multi-agent chemotherapy improves R0 resection rate and median disease-free survival (DFS) in patients with borderline resectable pancreatic adenocarcinoma (PDAC). Precise delineation and treatment planning are essential, and robust radiotherapy quality assurance (QART) is critical to optimize therapeutic outcomes. We report here the results of the Belgian dummy run, focusing on quantitative analysis of two benchmark cases. Material/Methods: A dummy run was conducted as part of the STEREOPAC QART process prior to patient enrolment in nine Belgian RT centers. Two representative cases of varying complexity were selected. Target volumes (tumour, tumour-vessel interfaces [TVI], internal target volumes [ITV]) and organs at risk (OARs) were delineated on portal phase contrast-enhanced planning CT. Supporting available imagings (MRI, PET- CT, 4D-CT), endoscopic reports, and clinical summaries were provided. Contours submitted by participating centers were compared to reference contours validated by an expert abdominal radiologist. Agreement was assessed in two rounds (pre- and post- feedback) using volume metrics, Dice Similarity Coefficient (DSC) and Mean Distance to Agreement (MDA). Results: Delineation of major gastrointestinal OARs and great vessels showed satisfactory inter-center consistency. Only two centers required significant corrections for vascular structures; other OARs needed minor or no adjustments. Volume discrepancies for the colon and jejunum–ileum were noted but had no clinical impact, as some centers extended delineation beyond protocol specifications. (Figure 1 - Volumes of OARs
contours submitted by the participating centers for the two Dummy Run cases of the STEREOPAC trial.)
Target delineation showed greater variability, prompting post-QART revisions in six centers. DSC values indicated moderate to poor agreement for ITV_T, GTV, and TVI, while MDA remained acceptable for GTV and ITV_T ( ≤ 4mm), but was notably poor for TVI. (Figure 2 - a. Comparison of submitted target volumes before and after the QART review feedback, b. DICE similarity coefficient obtained for the target volumes, and c. MDA for the target volumes.)
Conclusion: This dummy run highlights the complexity of
consistent target delineation in PDAC and underscore the importance of a preparatory QART phase. These findings support the implementation of detailed contouring guidelines and strict prospective QART for all patients randomized to the experimental iHD-SBRT arm of the STEREOPAC trial. References: 1. Bouchart C, Navez J, Borbath I et al. Preoperative treatment with mFOLFIRINOX (or Gemcitabine/Nab- paclitaxel) +/- isotoxic high-dose Stereotactic Body Radiation Therapy (iHD-SBRT) for borderline resectable pancreatic adenocarcinoma (the STEREOPAC trial): study protocol for a randomised comparative multicentre phase II trial. BMC Cancer 2023; 23 (1), 1-132. Weber, D. C., Tomsej, M., Melidis, C., & Hurkmans, C. W. QA makes a clinical trial stronger: evidence-based medicine in radiation therapy. Radiotherapy and Oncology 2012, 105(1), 4-8 Keywords: Pancreatic cancer, QART, prospective trial
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