S2269
Physics - Intra-fraction motion management and real-time adaptive radiotherapy
ESTRO 2026
(p>0.05). sCT-based dose recalculations showed mean reductions of 8% for the heart (range 2–13%, p<0.05) and 10% for the LAD (range 0.5–16%, p<0.05).Breast + nodal plans showed slightly larger variability (left lung +4.5%, right lung +3.5%, max 7%), with mean heart dose reduction of 10% (range 3–16%, p<0.05) and LAD reduction of 8% (range 2–10%, p<0.05). Automated sCT generation and dose recalculation were completed within 5 minutes. Monte Carlo verification confirmed the dosimetric robustness of DIBH plans. Conclusion: Automated adaptive dose recalculation from CBCT- based sCTs is feasible and reliable for DIBH breast radiotherapy on the Halcyon system. Minimal inter- and intrafraction anatomical variations confirmed the reproducibility of AlignRT Inbore-guided DIBH, supporting the integration of adaptive workflows for
MRI guided liver stereotactic body radiation therapy strategy for implementation on the MR-linac[2] T van der Lindt e.a., 2021, RadOnc, Evaluation of accumulated dose with residual uncertainties: an example with 4D-MRI guided liver SBRT Keywords: Dose accumulation, Liver SBRT, MR-Linac Digital Poster Highlight 4328 Reproducibility and Dosimetric Impact of Surface- Guided DIBH breast radiotherapy using an automated CBCT–synthetic CT workflow on Halcyon System Daniel NGUYEN 1 , Francesca di Franco 2 , Sena YOSSI 3 , Mustapha KHODRI 1 1 Physics, ORLAM, LYON, France. 2 Applications Cliniques, IRUDIGI, BAYONNE, France. 3 Radiotherapy, ORLAM, LYON, France Purpose/Objective: To evaluate the reproducibility of the Deep Inspiration Breath Hold (DIBH) technique guided by surface- guided radiotherapy (SGRT) and daily kilovoltage cone- beam CT (kV-CBCT) on the Halcyon system for left- sided breast cancer, we quantified pulmonary volume consistency between the planning CT and repeated CBCTs, and assessed dosimetric impacts on heart and left anterior descending artery (LAD) doses using an automated adaptive workflow based on CBCT-derived
daily dose verification in clinical practice. Keywords: SGRT-guided DIBH, Breast RT, Reproducibility
Digital Poster 4380
Investigation of the Use of External Abdominal Information in DIBH for Mediastinal Lymphoma Patients Kenneth Wikström 1,2 , Karin Andersson 3 , Safa Helal 4 , Marika Enmark 5 , Anneli Edvardsson 6 , Daniel Molin 7,8 , Anna Flejmer 2,8 1 Medical Physics, Uppsala University Hospital, Uppsala, Sweden. 2 Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden. 3 Medical Physics, The Skandion Clinic, Uppsala, Sweden. 4 Nuclear and Particle Physics, Uppsala University, Uppsala, Sweden. 5 Radiation Physics, Department of Hematology, Oncology and Radiation Physics, Skåne University Hospital, Lund, Sweden. 6 Medical Radiation Physics, Department of Clinical Sciences Lund, Lund University, Lund, Sweden. 7 Immunology, Genetics and Pathology, Uppsala University Hospital, Uppsala, Sweden. 8 Oncology, Uppsala University Hospital, Uppsala, Sweden Purpose/Objective: Proton radiotherapy for mediastinal lymphoma patients can spare normal tissue compared to photon radiotherapy because protons have a finite range. The treatment is often delivered during deep inspiration breath hold (DIBH), mainly to retract the heart out of the high-dose treatment field, but also to reduce uncertainties related to breathing motion. The reproducibility of the mediastinum in DIBH position is, for some patients, an issue, even though the breathing measure in terms of vertical displacement of the thorax ( Δ T) at a thoracic point (TP) is constant within a gating window. The aim of this study is to assess
synthetic CTs (sCTs). Material/Methods:
Ten consecutive left-sided breast cancer patients treated with DIBH guided by AlignRT Inbore (V7.2) were analyzed: five with breast-only IMRT plans and five with breast plus nodal VMAT plans (including internal mammary, supraclavicular, and axillary nodes). For each fraction, an initial CBCT (CBCT1) was acquired for setup verification and compared with the planning CT. After couch corrections, a second CBCT (CBCT2) was obtained to assess intrafraction motion. Dosimetric analyses were performed within the Mozi Adaptive Platform (V4.0.4.3, Manteia), which generates AI-based sCTs from CBCT images. The original treatment doses, computed using Eclipse v18.1 (IMRT) or RayStation 2024B (VMAT), were recalculated on the simulation CTs and generated sCTs from CBCTs using Mozi’s Monte Carlo dose algorithm. A total of five CBCT1 and five CBCT2 images were acquired per patient. Pulmonary volumes and mean heart and LAD doses were extracted from the planning CT, CBCT1, and CBCT2. Statistical comparisons were performed using Wilcoxon signed-rank tests. Results: Across 50 fractions, breast-only plans showed minimal pulmonary variation (left lung +1.7%, right lung +2.1%, p<0.05) and no significant intrafraction change
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