S592
Clinical – Head & neck
ESTRO 2026
predominantly originate within the pre-treatment FDG-PET-avid volume (GTV-PET) (1). Adequate dose delivery to high-dose regions is therefore critical. Anatomical changes during RT can cause deviations between the planned and delivered dose. This study aimed to examine discrepancies between planned and accumulated dose in regions of LRR. Material/Methods: Patients with biopsy-proven LRR after curatively intended radiotherapy for OPSCC treated between 2009 and 2017 were identified (1). Recurrence volumes were delineated on the recurrence scan, deformably registered to the planning CT (pCT), and the point of origin (PO) was determined on pCT according to Due et al. (2). A one-cm-diameter sphere was created around each PO to account for delineation- and registration uncertainties. Figure 1 provides an overview of the workflow for dose accumulation performed in Eclipse and Velocity. The pCT was deformably registered to each daily cone- beam CTs to generate a synthetic CT (synCT) for each fraction. The fraction doses were then recalculated on the synCTs and mapped back to the pCT. The fraction doses were summed to obtain the accumulated dose. Accumulated dose in the PO and the minimum and maximum dose within the sphere were extracted and normalized to the planned dose. A dose gradient (Gy/cm) of the sphere was calculated to estimate an uncertainty-range of the accumulated dose. Planned and accumulated doses were compared using two- sided paired t-test.
Conclusion: Compared with nodal size, necrosis, or bilateral involvement, stratification based on involved structures more effectively discriminates the prognostic differences of advanced CLN ENE in NPC patients. N1/N2 patients with either high-risk or intermediate-risk CLN ENE have outcomes relatively close to those with N3 disease but exhibit substantial heterogeneity. References: Pan J-J, Mai H-Q, Ng WT, Hu C-S, Li J-G, Chen X-Z, et al. Ninth Version of the AJCC and UICC Nasopharyngeal Cancer TNM Staging Classification. JAMA Oncol 2024. https://doi.org/10.1001/jamaoncol.2024.4354. Keywords: Extranodal Extension,Nasopharyngeal carcinoma Accumulated delivered dose in oropharyngeal carcinoma: did areas of later recurrence have unintended cold spots? Anne Marie Lindegaard 1 , Hristo A. Georgiev 1,2 , Ane Appelt 1,3 , Mogens Bernsdorf 1 , Anita B. Gothelf 1 , Claus A. Kristensen 1 , Jens Petersen 1,2 , Lena Specht 1,4 , Emin Tavlayan 1 , Ivan R. Vogelius 1,4 , Jeppe Friborg 1,4 , Katrin E. Håkansson 1 1 Department of Oncology, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark. 2 Department of Computer Science, University of Copenhagen, Copenhagen, Denmark. 3 Department of Health Technology, Technical University of Denmark, Copenhagen, Denmark. 4 Faculty of Health and Medical Science, Institute of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark Purpose/Objective: Locoregional recurrences (LRR) after radiotherapy for oropharyngeal squamous cell carcinoma (OPSCC) Digital Poster 2225
Results: Thirty-five patients with 49 recurrences were included in the analysis. Discrepancies between planned and accumulated dose in the recurrence PO were small, ranging from − 1.6 to 1.5 Gy (Figure 2). The per-patient difference between accumulated and planned dose was non-significant; mean − 0.1 Gy (95% CI − 0.28;0.08 Gy, p = 0.28). The median dose gradient within the one-cm-sphere was 2.8 Gy/cm (IQR: 1.7;4.0).
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