S848
Clinical - Lung
ESTRO 2026
Digital Poster 4590 Adaptive radiotherapy in locally advanced lung cancer: What is the benefit? Oumayma Mezouari, Othmane Saqri, Hicham Gazanayi, Omar Baddi, Wafaa Merssetti, Soukaina Morchid, Nabila Sellal Radiotherapy, Mohammed VI University Hospital Center, Tangier, Morocco Purpose/Objective: Lung cancer remains the leading cause of cancer- related mortality worldwide. Radiotherapy is a major therapeutic approach in locally advanced stages. Adaptive radiotherapy, which adjusts volumes and doses according to tumor and anatomical evolution, offers a promising personalized approach. Our study aims to evaluate the dosimetric impact of adaptive radiotherapy in locally advanced lung cancer. Material/Methods: This was a retrospective study including patients with locally advanced lung cancer treated with adaptive radiotherapy between April 2017 and October 2025 at the Radiotherapy Department of Mohammed VI University Hospital in Tangier. Results: Our study included 48 patients (median age 59 years [45–81 years], male to female ratio 3:1). Adenocarcinoma represented 66.7% of cases. Locally advanced stages were predominant (IIIC: 41.7%; IIIB: 25%), and 75% of patients had upper lobe tumors. All patients received chemoradiotherapy preceded by induction chemotherapy in 83.3%. Regarding technique, 83.3% of patients were treated with 3D-CRT and 16.7% with VMAT, with doses ranging from 60 to 66 Gy. Plan adaptation occurred at the 20th fraction (44 patients) or 15th fraction (4 patients), motivated by tumor shrinkage, initially high dosimetric constraints to organs at risk, or anatomical modifications. Dosimetric analysis showed significant target volume reduction, with a mean decrease in PTV of 27.75% (326.83 cm ³ , p = 0.002) and in CTV of 24.78% (183.72 cm ³ , p = 0.005), while maintaining stable tumor coverage (V95%: -0.48%, p = 0.567; D95%: +0.08%, p = 0.880). For organs at risk, significant reductions were achieved: lung parameters (V20: -38.49%, p = 0.011; V5: -28.85%, p = 0.001; Dmean: -14.23%, p = 0.034), cardiac parameters (V40: -76.82%, p = 0.001; V30: - 15.38%, p = 0.021; Dmean: -13.67%, p = 0.070), and spinal cord parameters (Dmax: -27.36%, p < 0.001). For the esophagus, we observed a decrease in V60 (- 35.57%, p = 0.417) and a moderate increase in Dmax (+7.78%, p = 0.236). Conclusion: Adaptative radiotherapy significantly reduces doses to organs at risk (lungs, heart, spinal cord) while maintaining optimal tumor coverage. These results
CI 2.78–5.67, p<0.001) (Figure 1). Spline modelling demonstrated a non-linear association between GTV and 2-year mortality, with risk rising sharplyfor GTV > 50 cc and plateauing beyond ~300 cc.
Conclusion: In this retrospective cohort, DC12m was a strong, independent predictor of OS after curative-intent hypofractioned radiotherapy for NSCLC. Patients without DC12m had an approximately four-fold higher mortality risk. These findings support using DC12 as a pragmatic, prognostically meaningful endpoint to guide conversations with patients, clinical follow-up and inform trial design. References: 1. Green MR, Cox JD, Ardizzoni A, Arriagada R, Bureau G, Darwish S, Deneffe G, Fukuoka M, Joseph D, Komaki R, et al. Endpoints for multimodal clinical trials in stage III non-small cell lung cancer (NSCLC): a consensus report. Lung Cancer. 1994 Nov;11 Suppl 3:S11-3. Keywords: Green, radiotherapy, lung
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