S2123
Physics - Inter-fraction motion management and daily adaptive radiotherapy
ESTRO 2026
contoured. For the daily treatment adaptation, we re- optimized the baseline plan on the dCT. To assess the impact of DIR uncertainties on the dose distribution, we performed a forward calculation of the MR-only adapted plan on the daily in-room CT, and compared the target and organs at risk (OAR) coverage on both
improving adaptive workflows and progressing towards online adaptation. The integration of synthetic imaging into clinical workflows highlights the need for standards and guidelines defining requirements, commissioning and QA of (synthetic) image quality. Based on the survey results and a subsequent EPTN workshop in 2025, a DELPHI process to reach consensus on these points is currently in preparation. References: [1] Trnkova et al. PhiRO 2023, https://doi.org/10.1016/j.phro.2023.100442 Keywords: particle therapy, adaptive, EPTN Digital Poster Highlight 1218 An automated workflow for daily MRI-guided adaptive liver SBRT with carbon ions Rita Pestana 1,2 , Sebastian Regnery 1,2 , Friderike Longarino 1,2 , Cedric Beyer 1,2 , Jakob Liermann 1,2 , Jürgen Debus 1,2 , Sebastian Klüter 1,2 , Katharina Seidensaal 1,2 , Julia Bauer 3 1 Department of Radiation Oncology and Heidelberg Ion Beam Therapy Center (HIT), Heidelberg University Hospital, Heidelberg, Germany. 2 Heidelberg Institute for Radiation Oncology (HIRO), National Center for Radiation Research in Oncology (NCRO), Heidelberg, Germany. 3 Department of Radiooncology and Radiotherapy, Charité – Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and HumboldtUniversität zu Berlin, Berlin, Germany Purpose/Objective: Carbon ion radiotherapy (CIRT) has shown good treatment outcomes for hepatocellular carcinoma (HCC) patients [1], [2]. At the Heidelberg Ion-Beam Therapy Center (HIT), the prescription is typically delivered as stereotactic body radiotherapy (SBRT), requiring high geometrical precision. We present a new automated MRI-online-adaptive carbon ion liver SBRT pipeline to daily adapt the treatment of HCC lesions. The feasibility of this workflow was retrospectively tested on liver SBRT patients treated at HIT. Material/Methods: A cohort of four patients with a total of five fraction MR images was considered. All the patients had the same dose prescription, 4 x 10.5 Gy(RBE) CIRT, and daily MR and in-room CT imaging before the treatment. We developed an automated pipeline in a research version of RayStation 2024B to generate a daily deformed CT (dCT) from the daily MRI with deformable image registration (DIR) [3]. We considered different DIR approaches: grey level-, liver- and GTV-based. For each scenario, we compared the structures generated with DIR against those manually
images. Results:
The different DIR approaches performed similarly for the OAR in terms of dice similarity coefficient (DSC) (Figure 1). For the plan adaptation, we used the dCT generated with a GTV-based approach, to ensure a more accurate deformation of the targets. The target coverage obtained on the dCT is in accordance with the values calculated on the daily CT. For the OAR, some deviations on the dose at 0.1 cc (near-maximum dose) were observed (Figure 2). The maximum computational time required to generate the dCT and re-optimize the baseline plan on this image was six minutes.
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