S814
Clinical - Lung
ESTRO 2026
carcinoma, and 1 small-cell lung carcinoma. Three patients received concurrent chemotherapy with conventionally fractionated reRT (60 Gy(RBE)/30 fractions), while the remainder underwent hypofractionated IMPT alone (45–60 Gy(RBE)/15–20 fractions). Results: Upright IMPT achieved comparable target coverage to supine IMPT and VMAT. Compared with VMAT, IMPT significantly reduced OAR exposure: lung V5 32.2% vs 12.5% (p=0.007); mean heart 4.28 Gy vs 1.83 Gy(RBE) (p=0.010); mean esophagus 10.98 Gy vs 3.18 Gy(RBE) (p=0.023); and spinal cord Dmax 14.4 Gy vs 4.8 Gy(RBE) (p=0.003). Lung volume increased 9.8% in the upright position (p<0.01). No significant dosimetric differences were found between upright and supine IMPT (Fig.2).
Proffered Paper 3242
Prospective Clinical Trial of Upright Image-Guided Intensity-Modulated Proton Therapy for Thoracic Re-Irradiation: Interim Analysis Philip Blumenfeld 1 , Aviad Berger 1 , Alexander Pryanichnikov 2,3 , Daniel Levy 1 , Yair Hillman 1 , Marcel Fang 1 , Sarit Appel 4 , Jon Feldman 1 , Aron Popovtzer 1 1 Sharett Institute of Oncology, Hadassah Medical Center, Hebrew University of Jerusalem, Jerusalem, Israel. 2 Institute of Biomedical Engineering, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany. 3 Division of Biomedical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany. 4 Department of Radiation Oncology, Sheba Medical Center, Tel Hashomer, Israel Purpose/Objective: Thoracic re-irradiation (reRT) for locally recurrent non– small cell lung cancer (NSCLC) is limited by cumulative dose constraints to mediastinal organs-at-risk (OARs). Proton therapy enables sharper dose gradients and lower normal-tissue exposure compared with photon techniques, while upright positioning may further improve lung expansion, displace the heart inferiorly, and increase treatment accessibility with gantry-less systems. This planned interim analysis of ongoing prospective clinical trial evaluates feasibility, dosimetry, and early oncologic outcomes of upright intensity-modulated proton therapy (IMPT) for thoracic
At three months, 5 patient have complete, 3 partial metabolic response and 2 stable disease with only grade 1–2 fatigue or cough (30%) and no grade ≥ 3 events. Conclusion: Upright IMPT using an ITV-based approach is feasible and well tolerated for thoracic re-irradiation, providing robust target coverage and significant OAR sparing compared with VMAT. Enhanced lung expansion, favorable early metabolic responses support continued accrual and long-term evaluation of upright proton therapy as an innovative strategy for central thoracic reRT. References: 1. Feldman J, Pryanichnikov A, Achkienasi A, et al. Commissioning of a novel gantry-less proton therapy system. Front. Oncol. 2024; 14:1417393. doi: 10.3389/fonc.2024.1417393.2. Feldman J, Pryanichnikov A, Shwartz D, et al. Study of upright patient positioning reproducibility in image-guided proton therapy for head and neck cancers. Radiother Oncol. 2024; 201:110572. doi: 10.1016/j.radonc.2024.110572.3. Blumenfeld P, Pryanichnikov A, Hillman Y, et al. Prospective clinical trial of upright image-guided proton therapy for locally recurrent head and neck and brain malignancies. Radiother Oncol. 2025; 211:111097. doi:10.1016/j.radonc.2025.111097 Keywords: Upright proton therapy, lung cancer re- irradiation
reRT compared with supine IMPT and photon volumetric-modulated arc therapy (VMAT). Material/Methods: Ten patients with locally recurrent thoracic
malignancies previously treated with radiotherapy were prospectively enrolled in an ongoing study of upright reRT using a novel proton therapy system (Fig.1) [1-3]. Nine patients underwent both upright and supine simulations under free-breathing conditions using an internal target volume (ITV) approach to account for respiratory motion, one patient completed only the upright workflow. Comparative treatment plans were generated for upright/supine IMPT and VMAT. Dose–volume parameters for lung, heart, esophagus, spinal cord were analyzed. Lung volume differences between positions were quantified, toxicity graded per CTCAE v5.0, and early response assessed by PET-CT (n=8) or CT (n=2) at three months.
Median age was 70.2 years, two patients were female. Histologies included 8 NSCLC, 1 adenoid cystic
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