S2227
Physics - Intra-fraction motion management and real-time adaptive radiotherapy
ESTRO 2026
MLC modifier program to improve fiducial detection for MV/kV imaging during hypofractionated prostate volumetric modulated arc therapy. J Appl Clin Med Phys. 2019;20(6):120-124. doi:10.1002/acm2.12614Omotayo A, Venkataraman S, McCurdy B. Constrained optimization towards marker- based tumor tracking in VMAT. Biomed Phys Eng Express. 2020;7(1) doi:10.1088/2057- 1976/abce0cBerbeco, PhD., ed Beam's eye view imaging in radiation oncology. CRC Press, 2017.Chrystall, D., Stewart, M., Jin, F., et al. 2025 Experimental investigation of real-time 3D beam's eye view image-guided radiotherapy for prostate SBRT. Medical Physics, 52(11), p.e70086 Keywords: Prostate, tracking, beam-view Poster Discussion 2022 Online decision support for adaptive breast proton therapy using surface-guided dose prediction Vincent C Hamming, Daniele Cannavò, Mihnea G Steiu, Noor Panneman, Gabriel G Marmitt, John H Maduro, Johannes A Langendijk, Nanna M Sijtsema, Stefan Both Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, Groningen, Netherlands Purpose/Objective: Whenever feasible, non-ionizing imaging modalities should be prioritized over radiation-based techniques to minimize cumulative patient dose and associated lifetime risks. While Cone-beam CT (CBCT) is commonly used for patient positioning and assessing breast deformations, Surface Guided RadioTherapy (SGRT) offers a non-ionizing alternative. This study evaluates the feasibility of replacing CBCT with SGRT for monitoring breast surface deformations in proton therapy and subsequent dosimetric assessments, enabling timely identification of patients needing plan adaptation. Material/Methods: Forty-six breast cancer patients treated with proton therapy to the right or left breast or thoracic wall, with or without lymph nodes, were included. Treatment planning was performed in RayStation using 2–3 anterior beams with ~40° hinge angles. Synthetic CTs were generated from the planning CT (pCT) simulating 50 unique breast expansions/contractions. Dosimetric consequences for the CTV (D98% relative to the prescribed dose) and heart (mean heart dose, MHD) were assessed by recalculating the original treatment plan on these synthetic CTs. The Dutch clinically employed NTCP model (Boersma et al.) was used to determine the life time risk for acute coronary events (ACE) based on the MHD.Surface meshes derived from the BODY contour from the pCT and synthetic CTs
Figure 1 Flowchart of the beam-view tracking clinical workflow for prostate SABR. Results: Beam-view tracking was successfully implemented in 53 of 54 treatment fractions, yielding a feasibility estimate of 98.2%, 95% CI (90.1%, 100%). Fifty-one treatment interruptions were observed, of which 65% resulted in a couch shift ≥ 1.5 mm, 23% in ≥ 3 mm, and 5% in ≥ 5 mm. Accuracy from retrospective kV/MV triangulation was 0.2 ± 1.2 mm (superior-inferior), 0.2 ± 1.2 mm (anterior-inferior), and 0.3 ± 1.3 mm (left- right). Dose reconstructions demonstrated dose distributions closer to planned with beam-view tracking than without (Figure 2). No grade ≥ 3 GU or grade ≥ 2 GI acute toxicities were observed.
Figure 2 Waterfall plot of the dose differences between planned GTV D95% and the delivered dose with gating (blue) and estimated dose without gating (orange) per patient. Conclusion: This study demonstrates the safety and feasibility of beam-view tracking for accessible real-time 3D IGRT in prostate SABR, supporting its potential for wider clinical implementation. References: Happersett L, Wang P, Zhang P, et al. Developing a
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