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ESTRO 2026
calculation in the thorax… Physica Medica 2022;103:157–65. doi.org/10.1016/j.ejmp.2022.10.012.[2]
post-adaptation dose differences were higher (Fig.1). After adaptation, interfraction dose variability decreased significantly for targets and most organs (Levene, FDR-adjusted p<0.05). Five fractions showed ≥Δ 5% underdosage in CTVp, eight in CTVn, though no accumulated CTV underdosage occurred over patients. The esophagus exceeded dose-guidance levels in 81% of fractions, but only 32% of fractions surpassed the Δ 5% threshold. For the spinal canal, 21% of fractions exceeded Δ 5%, and 5% exceeded Δ 10%. Three patients had accumulated D0.03cc above clinical limits. The number of patients exhibiting | ≥Δ 3%| dose trends remained comparable before (N=18) versus after adaptation (N=19) with mainly trends in esophagus and heart. Higher dose difference trends (| ≥Δ 10%|) occurred less frequently in patients after adaptation (N=12 vs N=8). Trend durations were consistent, spanning 4-6 fractions (Fig.2).
Thomsen
SN, et al. Daily CBCT-based dose calculations for enhancing the safety of dose-escalation in lung cancer radiotherapy. Radiotherapy and Oncology 2024;200:110506. doi.org/10.1016/j.radonc.2024.110506.[3] Callens D, et al. Is full-automation in radiotherapy treatment planning ready for take off? Radiotherapy and Oncology 2024;201:110546. doi.org/10.1016/J.RADONC.2024.110546.[4] Parke r W, et al. ICRU Report 50, ICRU; 1994.[5] Bradley JD, et al. RTOG 0617: a randomised, two-by-two
factorial … Lancet Oncol 2015;16:187–99. doi.org/10.1016/S1470-2045(14)71207-0.
Digital Poster Highlight 1921 Assessment of margin robustness in online adaptive bladder radiotherapy Pauline Hinault, Jessica Prunaretty, Dorian Trauchessec, Aurelie Morel, Nicolas Bizot, Morgan Michalet, Olivier Riou, David Azria, Norbert Ailleres Radiotherapy, Cancer Institute, Montpellier, France Purpose/Objective: Bladder radiotherapy is challenged by variations in bladder size, shape, and position during and between sessions (Deers-Ribers, 2014), which may cause target underdosing and/or organs at risk (OARs) overdosing (Astrom, 2022). At Montpellier Cancer Institute, the Ethos system (Varian) uses artificial intelligence (AI) for real-time online adaptive radiotherapy (oART).This study aimed to assess the benefits of this adaptive workflow and the robustness of the selected margins. Material/Methods: This retrospective study included 10 bladder cancer patients treated with 20 fractions of 2.75 Gy adaptive radiotherapy. PTVs, for the bladder, were defined with asymmetric margins: 8 mm in anterior, posterior and superior directions and 5 mm in left, right and inferior directions. 5 mm was used for lymph nodes. At each session, targets and OARs were automatically generated on the daily CBCT (CBCT1) using Ethos AI and reviewed by the radiation oncologist. A synthetic CT (sCT) was generated by deforming the planning CT to match CBCT1 anatomy. Two plans were computed on the sCT: the scheduled plan, recalculated from the initial plan, and the adaptive plan, optimized using updated contours. A final CBCT (CBCT2) was acquired before delivery to confirm anatomy.For each session, bladder and OARs were redefined on CBCT2, a delivered plan was obtained by recalculating the adaptive plan on this dataset and then compared with the scheduled and adaptive plans. Dosimetric
Conclusion: Automated CBCT-based dose calculations provide efficient daily and accumulated dose assessments, showing robust target coverage but organ of interest overdosages. Plan adaptation improved interfraction dose stability, confirming our adaptive strategy and supporting CBCT-based delivered dose monitoring as a practical tool for data-driven decision-making in offline adaptive radiotherapy. Keywords: CBCT dose calculations, adaptive
radiotherapy References: [1]
Thing RS, et al. Evaluation of CBCT based dose
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