S2455
Physics - Radiomics, functional and biological imaging, and outcome prediction
ESTRO 2026
radiation therapy for localised prostate cancer—a systematic review and meta-analysis,” Prostate Cancer Prostatic Dis, 2025, 10.1038/s41391-025-00961-0[2] [2] R. B. Tino et al., “Protecting organs-at-risk in cancer therapies through temporary organ displacement: a comprehensive review,” 2025, Frontiers Media SA, 10.3389/or.2025.1655365[3] [3] O. A. Houlihan et al., “A Randomized Feasibility Trial of Stereotactic Prostate Radiation Therapy With or Without Elective Nodal Irradiation in High-Risk Localized Prostate Cancer (SPORT Trial),” Int J Radiat Oncol Biol Phys, vol. 117, no. 3, pp. 594–609, Nov. 2023, 10.1016/j.ijrobp.2023.02.054 Keywords: rectal spacers, prostate, quality metrics Digital Poster 2960 Effect of ROI definition on PET radiomics model performance in HNSCC Michael Vácha 1,2 , Alex Zwanenburg 3,4 , Frank Hofheinz 2 , Fabian Lohaus 5 , Sebastian Zschaeck 6 , Sebastian Hoberück 7 , Pavel Nikulin 2 , Jens Maus 2 , Elia Lombardo 8 , Guillaume Landry 8 , Adrien Holzgreve 9 , Mechthild Krause 5,3 , Esther G C Troost 5,3 , Anja Braune 2,7 , Steffen Löck 3,1 1 Institute of Radiooncology - OncoRay, Dresden, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany. 2 Institute of Radiopharmaceutical Cancer Research, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany. 3 OncoRay-National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Helmholtz-Zentrum Dresden- Rossendorf, Dresden, Germany. 4 National Center for Tumor Diseases (NCT), NCT/UCC Dresden, a partnership between DKFZ, Faculty of Medicine and University Hospital Carl Gustav Carus, TUD Dresden University of Technology and Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden, Germany. 5 Department of Radiotherapy and Radiation Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany. 6 Department of Radiation Oncology, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany. 7 Department of Nuclear Medicine, University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany. 8 Department of Radiation Oncology, LMU University Hospital, LMU Munich, Munich, Germany. 9 Department of Nuclear Medicine, LMU University Hospital, LMU Munich, Munich, Germany
point in the prostate-rectum interface using Python (Fig.1). Median distances per point in the prostate- rectum interface were used for CBCT analysis. Metrics D3mm, D5mm, and D7mm were calculated and represent the percentage of distances greater than 3, 5, and 7 mm, respectively. Metrics were calculated across the full interface and within superior-inferior thirds: apex, midgland, and base + seminal vesicles.
Logistic regression was used to evaluate whether metrics were significant predictors of grade ≥ 1 RTOG late GI AE (p<0.05). Median spacing and interquartile ranges were calculated for patients grouped by adverse event status. Results: D5mm and D7mm were significant predictors of AE on MRI (fig.2) across the entire prostate; patients with no AE had median D5mm and D7mm of 100% (2%) and 100% (0%) compared to those who did; 99% (22%) and 93% (26%). Metrics computed on the entire prostate for planning or CBCT contours were not predictive of AE.
On planning contours, the prostate base was a significant predictor of AE for D3mm, D5mm, and D7mm metrics: patients with no AE had median values of 100% (0%), 100% (3%), and 95% (16%), compared to 98% (10%), 85% (25%), and 73% (40%). Prostate base spacing on CBCT was predictive of AE, most patients with D7mm<100% experienced AE (100% (11%) vs 90% (33%)). Metrics applied to the midgland and apex regions were not significant on any modality. Conclusion: A novel metric was identified for each imaging modality which was predictive of clinician reported AE. The use of manual contours or auto-contours demonstrates a method of spacer evaluation with a low time cost. Subdivisions of the prostate-rectum interface were identified as predictive of AE and will assist future spacer quality studies. References: [1] [1] C. H. M. Wong et al., “Does biodegradable peri-rectal spacer mitigate treatment toxicities in
Purpose/Objective: Due to its rising incidence, head and neck squamous
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