S2204
Physics - Intra-fraction motion management and real-time adaptive radiotherapy
ESTRO 2026
Poster Discussion 632
Hypofractionated Online Adaptive Radiotherapy for Locally Advanced NSCLC: Accounting for Daily Anatomy Variations to Isotoxically Dose Escalate Simran A Polce, Nour Nasser, John Peterson, Marian Hernandez, Jongmyung Kim, Jessica M Frakes, Nate Thorne, Ibrahim Oraiqat, Patty Cordero, Janelle Brewer, Jacqueline Andreozzi, Vladimir Semenenko, Gage Redler, Stephen A Rosenberg Radiation Oncology, H. Lee Moffitt Cancer Center, Tampa, USA Purpose/Objective: Dose escalation and hypofractionation are emerging options for locally advanced (LA) NSCLC patients ineligible for surgery or chemoradiotherapy (Westover, K et al.). However, unacceptable toxicity rates remain (G3-esophagitis up to 24%, G3-pneumonitis up to 12%) (Said, B. et al.). We evaluated the feasibility and dosimetric impact of daily online adaptive radiotherapy (oART) in LA NSCLC by quantifying daily target and Organ at Risk (OAR) doses, comparing adaptive (ADP) and scheduled (SCH) plans via daily and cumulative doses. We hypothesize that unrecognized OAR dose contributes to historically high toxicity, and that oART reduces OAR dose through daily hotspot migration while isotoxically maintaining target coverage. Material/Methods: Retrospective analysis of 180 oART sessions across 12 Stage II–III NSCLC patients treated in 15 fractions. oART workflow: image acquisition, patient modeling/contouring, plan generation/selection, IGRT verification (CBCT-to-CBCT), and treatment delivery. Targets receiving 300 cGy/fx were propagated/aligned daily; critical OARs were recontoured to account for intra-fraction variability. Volume to safely receive 400 cGy/fx was derived around daily OARs. Daily OAR (proximal bronchial tree [PBT]) and target (IGTV) doses were compared for SCH vs. ADP. Cumulative dose was evaluated for PBT and IGTV separately using structure- specific guided rigid fusion across all fractions. To account for inherent uncertainties of rigid fusion, cumulative PBT dose was assessed within a local (5mm) region (PBT_5mm).
Conclusion: Intrafraction gating and drift correction during MRI- guided SBRT of liver tumors generally improves GTV coverage over no IMM, especially in cases with large respiratory amplitudes. For cases with high treatment efficiency, a patient-specific approach with reduced PTV margins could be considered to fully exploit the advantages of IMM. References: [1] Grimbergen G, Hackett SL, van Ommen F, van Lier ALHMW, Borman PTS, Meijers LTC, de Groot-van Breugel EN, de Boer JCJ, Raaymakers BW, Intven MPW, Meijer GJ. Gating and intrafraction drift correction on a 1.5 T MR-Linac: Clinical dosimetric benefits for upper abdominal tumors. Radiotherapy and Oncology 2023;189;109932. Keywords: Liver tumors, dose accumulation, MRI- guided SBRT
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