S2205
Physics - Intra-fraction motion management and real-time adaptive radiotherapy
ESTRO 2026
Results:
Precision Hypofractionated Radiation Therapy in Poor Performing Patients With Non-Small Cell Lung Cancer: Phase 1 Dose Escalation Trial. Int J Radiat Oncol Biol Phys. 2015;93(1):72-81. doi:10.1016/j.ijrobp.2015.05.004 Keywords: Adaptive RT, Dose Escalation, Isotoxicity Digital Poster Highlight 721 Bronchial Correlation Objects for improved tumour localization on stereoscopic X-ray images Julius Arnold 1,2 , Hannah Jungreuthmayer 1,2 , Kajetan Berlinger 3 , Wolfgang Lechner 1,2 , Andreas Renner 1,2 , Martin Heilmann 1,2 , Joachim Widder 1,2 , Dietmar Georg 1,2 , Barbara Knäusl 1,2 1 Department of Radiation Oncology, Comprehensive Cancer Center Vienna, Medical University of Vienna, Vienna, Austria. 2 Christian Doppler Laboratory for Image and Knowledge Driven Precision Radiation Oncology, Medical University of Vienna, Vienna, Austria. 3 Brainlab SE, Brainlab SE, Munich, Germany Purpose/Objective: For real-time image-guided lung cancer radiotherapy based on stereoscopic X-ray images, tumour localization remains a challenge, especially for small lesions in low-contrast and anatomically obscured scenarios. Defining a new anatomical surrogate, referred to as “Correlation Object”, by adding surrounding bronchial structures to the gross tumour volume (GTV), has shown potential for accurate and reliable tumour localization [1]. This proof-of-concept study examined the ability to register the Correlation Object with stereoscopic X-ray images including the impact of object size. Material/Methods: Four-dimensional computed tomography scans (4DCTs) of 31 patients with lung tumours (19 T1-Stage; 12 T2) were retrospectively collected (IRB:1359/2025). Based on the inspiration and expiration phase of the 4DCT, stereoscopic X-rays were simulated for an ExacTrac Dynamic System (Brainlab SE, Munich) using the clinical standard settings (110kV, 16mAs). The simulation included calibration geometry, X-ray spectrum, attenuation coefficients, and incident intensities of the Beer-Lambert law.The amount of motion of each voxel in the ipsilateral lung contour was estimated via deformable image registration of one 4DCT phase to all other phases. Voxels moving similar to the GTV were grouped to a Correlation Object.The size of the Correlation Object was defined by tissue (lung and bronchi) moving similar to the GTV within a predefined tolerance threshold, ranging from 0mm (GTV-only) to the maximum covering all bronchial structures. The object’s digitally reconstructed radiographs were 6D-registered to the
Median follow-up: 6 months. One G3 toxicity: pneumonitis in a patient with prior lung RT, lobectomy, and immunotherapy-related pneumonitis. Average oART session time (CBCT acquisition to treatment completion) was 31.2 ± 6.9 min. ADP daily PBT D0.03cc was 359 cGy (327–372) vs. 392 cGy (331– 466) in SCH, a 7.9% decrease. Figure 1A/B:Improved PBT sparing in a single fraction. Figure 1.C:Distribution of daily PBT maximum dose(D0.03cc), ADP vs. SCH for
each patient. Figure 1D/E:Target coverage improvement in a single fraction. Figure
1.F:Distribution of daily IGTV V6000cGy(400cGy/fx), ADP vs. SCH for each patient. Daily IGTV V400cGy was comparable (mean +3.0 ± 13.9%, favoring ADP). Cumulative PBT_5mm D0.03cc decreased 1.4%. Figure 2:Representative hotspot migration and cumulative DVH showing reduced heterogeneity over treatment with ADP. Conclusion: This study demonstrates a novel oART approach for LA NSCLC. Daily PBT D0.03cc decreased 7.9% while maintaining target coverage. Daily hot spot migration shows reduced OAR dose and heterogeneity in cumulative doses. Daily oART shows clear dosimetric benefit, allowing for feathering of a simultaneous integrated boost while accounting for intra-fraction OAR variation for isotoxic delivery. References: Said BI, et al. Accelerated Hypofractionated Radiotherapy for Locally Advanced NSCLC: A Systematic Review From the International Association for the Study of Lung Cancer Advanced Radiation Technology Subcommittee. J Thorac Oncol. 2025;20(1):39-51. doi:10.1016/j.jtho.2024.09.1437Westover KD, et al.
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