S599
Clinical – Head & neck
ESTRO 2026
iDENIF was reported. Two reviewers extracted data. Logit-transformed proportions were pooled using a random-effects generalized linear mixed model (study- level random intercept). Prespecified study-level subgroup analyses included treatment setting, de- intensification strategy, and predominant tumor type. Results: To date, from 11,319 records, 31 studies (n=3,156) met the criteria. The pooled iDENIF rate was 1.1% (95% CI, 0.7–1.6). In definitive radiotherapy iDENIF was 0.8% (0.4–1.5; I ² 16.9%, τ² 0.17) and in postoperative radiotherapy 1.8% (1.0–3.2; I ² 0.0%, τ² 0.00). Within the definitive setting, iDENIF was 0.4% (0.1–1.2) for volume de-intensification, 0.8% (0.4–1.8) for dose de- intensification, 1.5% (0.9–2.6) for combined volume and dose de-intensification, and 0.6% (0.1–4.1) for complete ENI omission; heterogeneity was negligible within de-intensification strategies (I ² 0%, τ² 0.00). Grouping definitive radiotherapy studies by predominant tumor type, iDENIF was 0.4% (0.1–2.4; I ² 26.4%, τ² 0.49) for HPV-associated oropharyngeal carcinoma, 0.5% (0.1–2.5; I ² 50.8%, τ² 1.00) for nasopharyngeal carcinoma, and 1.4% (0.7–2.8; I ² 0.0%, τ² 0.00) for other/mixed primaries. Conclusion: Isolated failures within de-intensified elective volumes are rare. Across treatment settings, de-intensification strategies, and primary sites, preliminary estimated rates were well below thresholds commonly used to judge de-intensification safety, supporting feasibility in contemporary practice. Risk of bias, time-to-event, and toxicity outcomes will be presented at the conference. These results may guide the clinical implementation of elective radiotherapy de-intensification for head and neck cancer. Keywords: De-Escalation, Systematic Review, Meta- Analysis Validation and development of the 9th AJCC/UICC N classification for nasopharyngeal carcinoma in non-endemic regions of China: a multicenter study Tong Jin, Tong Bu, Junyi Liu, Lirong Wu, Xia He Department of Radiation Oncology, Jiangsu Cancer Hospital & Jiangsu Institute of Cancer Research & Affiliated Cancer Hospital of Nanjing Medical University, Nanjing, China Purpose/Objective: The 9th edition of the AJCC/UICC staging system for nasopharyngeal carcinoma (NPC) incorporates advanced extranodal extension (ENE) into the N3 classification for the first time. [1,2] Our study aims to validate the applicability of the new N classification in non-high-incidence regions and to evaluate the Mini-Oral 2622
Conclusion: Deep learning-based skeletal muscle quantification provides accurate, reproducible, and clinically meaningful body composition metrics. Muscle indices at cervical and thoracic vertebral levels are reliable surrogates for outcome prediction when L3 is excluded from imaging, supporting the feasibility of fully automated sarcopenia assessment in HNSCC management. References: 1. Grossberg AJ et al. JAMA Oncol. 2016;2(6):782– 789. 2. Ye Z et al. JAMA Netw Open. 2023;6(8):e2328280. 3. Isensee F et al. Nat Methods. 2021;18(2):203–211. 4. Naser MA et al. Front Oncol. 2022;12:930432. 5. Prado CM et al. Lancet Oncol. 2008. 9(7):10.1016 Keywords: Whole-body Muscle,Sarcopenia, Prognostic Biomarker Isolated nodal failures after de-intensified elective radiotherapy in head and neck cancer: systematic review and meta-analysis Florian Stritzke 1,2 , Philipp Schröter 2,3 , Johannes Vey 4 , Leonhard Doersam 2 , Jürgen Debus 2,3 , Thomas Held 2,3 1 Heidelberg Faculty of Medicine, Heidelberg University, Heidelberg, Germany. 2 Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg, Germany. 3 Clinical Cooperation Unit Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany. 4 Department of Medical Biometry, University of Heidelberg, Heidelberg, Germany Purpose/Objective: Elective nodal irradiation (ENI) can sterilize subclinical disease, but improved staging and the morbidity associated with large cervical volumes challenge the extent of current elective treatment. For patients receiving de-escalated treatment, we estimated the rate of isolated de-intensified ENI failure (iDENIF)— without synchronous failure in high- or intermediate- risk areas—to determine oncological safety. Material/Methods: Following a PROSPERO-registered protocol Poster Discussion 2613 (CRD420251176891), we searched MEDLINE, Embase, and CENTRAL (01/2000–present). Prospective and retrospective studies of squamous cell head and neck cancer receiving de-intensified ENI were eligible if
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