S1529
Interdisciplinary - Quality assurance and risk management
ESTRO 2026
Digital Poster 3218
marker-less vDIBH SBRT protocol relying solely on offline IFI verification, without fiducials, gating, or ABC systems. Despite its simplicity, the workflow achieved geometric stability comparable to complex tracking methods, supporting anisotropic ITV–PTV margins of 4 mm (LR/AP) and 7 mm (SI). This approach demonstrated the feasibility of safe SBRT in vDIBH using standard imaging tools, offering a scalable and cost-effective solution for motion management.A prospective validation study is ongoing to confirm these data in a larger cohort References: 1 - Hoffmann L, Ehmsen Ml, Hansen J, et al (2023). Radiotherapy and Oncology 188:109887. https://doi.org/10.1016/j.radonc.2023.109887. 2 - Li R, Han B, Meng B, et al (2013). International Journal of Radiation Oncology*Biology*Physics 87:917–923. https://doi.org/10.1016/j.ijrobp.2013.08.015 3 - Kim T, Laugeman E, Kiser K, et al (2024). J Applied Clin Med Phys 25:e14242. https://doi.org/10.1002/acm2.14242. 4 - Prado A, Zucca D, De La Casa MÁ, et al (2022). Physics and Imaging in Radiation Oncology 22:57–62. https://doi.org/10.1016/j.phro.2022.04.004. 5 - Guberina M, Santiago A, Pöttgen C, et al (2023). Clinical and Translational Radiation Oncology 40:100628. https://doi.org/10.1016/j.ctro.2023.100628. Keywords: SBRT, vDIBH, Marker-less Intrafraction motion Advancing Trial Radiotherapy Quality Assurance (RTQA): AI-Assisted Contour Assessment using the AGITG TOPGEAR Trial Karen L Olden 1 , Phillip Chlap 2,3 , Rachel L O'Connell 4 , Alisha J Moore 5 , Martin A Ebert 6 , Annette Haworth 7 , Jason Dowling 8 , Matthew Field 2 , Tomas Kron 9 , Trevor Leong 1 , Mark T Lee 10 , Lois Holloway 2,3 1 Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne, Australia. 2 Medical Physics, UNSW and Ingham Institute for Applied Medical Research, Sydney, Australia. 3 Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Sydney, Australia. 4 National Health and Medical Research Council Clinical Trials Centre, University of Sydney, Sydney, Australia. Poster Discussion 3529 5 Research and Quality Assurance, Trans-Tasman Radiation Oncology Group, University of Newcastle, Newcastle, Australia. 6 Medical Physics, University of Western Australia, Perth, Australia. 7 School of Physics, University of Sydney, Sydney, Australia. 8 Australian e- Health Research Centre, CSIRO, Brisbane, Australia. 9 Medical Physics, Peter MacCallum Cancer Centre, Melbourne, Australia. 10 Radiation Oncology, Liverpool and Macarthur Cancer Therapy Centre, Sydney, Australia
Marker-less voluntary DIBH SBRT for lung and liver lesions: pilot derivation of ITV–PTV margins using intrafraction kV planar imaging Anna Merlotti 1 , Alberto Boriano 2 , Stefania Martini 1 , Luca Gianello 1 , Lavinia Spinelli 1 , Salvatore Dario Solla 1 , Francesco Olivero 1 , Paola Critelli 1 , Riccardo Vigna Taglianti 1 1 Radiotherapy, A.O. S.Croce e Carle Teaching Hospital, Cuneo, Italy. 2 Medical Physics, A.O. S.Croce e Carle Teaching Hospital, Cuneo, Italy Purpose/Objective: To evaluate the feasibility of a marker-less voluntary deep-inspiration breath-hold (vDIBH) workflow for stereotactic body radiotherapy (SBRT) of lung and liver lesions. This pilot study aimed to quantify intrafraction motion using offline analysis of intrafraction kV planar imaging (IFI) and derive directional ITV–PTV margins, providing a pragmatic approach for centers without fiducials or ABC systems. Material/Methods: Six consecutive patients (7 lung and 1 hepatic dome lesions) underwent vDIBH SBRT. An initial free- breathing CT (FB-CT) defined the anatomy and isocenter for daily setup. Each patient underwent three DIBH CTs (one for planning and two for reproducibility) to construct a patient-specific ITV. A 5 mm ITV–PTV margin was applied. Patients were positioned in FB, verified with CBCT in DIBH, and treated in vDIBH with a 4 mm tolerance (RPM/RGSC). During beam-on, kV planar images were acquired at predefined gantry angles. Only images with sufficient contrast and clear lesion visualization were analyzed. For the hepatic dome lesion, the diaphragmatic contour was used as a surrogate marker. Displacements were measured offline, aligning each visible lesion (or surrogate) with the ITV center on DRRs. Ninety-one images met the inclusion criteria. Margins were estimated as |μ| + 1.645·σ, covering ~95% of observed motion. Results: Mean ± SD displacements were x −0.05 ± 0.20 cm, y +0.05 ± 0.23 cm, z −0.13 ± 0.35 cm. Lateral and AP shifts were negligible, while SI showed the largest excursions.A small but consistent cranial shift (mean −0.13 cm) suggested slightly shallower inspiration during treatment compared to the planning DIBH CT, in line with Hoffmann et al. (1). Exceedances > ±5 mm occurred in 4.4% (x), 0% (y), and 16% (z). Derived ITV– PTV margins were 4 mm (LR/AP) and 7 mm (SI). Results were comparable to Li et al. (2), Kim et al. (3), and Prado et al. (4), and slightly lower than Guberina et al. (5) using automatic kV tracking. Conclusion: ConclusionThis proof-of-concept study introduces a
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