ESTRO 2025 - Abstract Book

S1517

Clinical – Mixed sites & palliation

ESTRO 2025

Results: In total, 52 patients were included, and 55 online adaptive treatments were performed. An adaptive plan was chosen in 58% of fractions and 78% of patients were treated with at least one adaptive plan. This resulted in a significantly higher given GTV D mean compared to the planned dose (100.6 BED 10 vs. 95 BED 10 , P< 0.001). The dose to D 0.5cc of the gastro-intestinal organs (GIO) was 2.3 Gy EQD 2 3 higher for the SOC plan on the fraction CT compared to the SOC plan on the original planning CT (P=0.009), this finding represents the dosimetric impact of inter-fraction motion without plan adaption. The GIO D 0.5cc was also 2.7 Gy EQD 2 3 higher (p=0.01) on the fraction CT with the given plan compared to the SOC plan on the planning CT scan. However, no significant difference in GIO D 0.5cc was found between the SOC plan on the fraction CT and the given plan on the fraction CT: this increased dose is not an effect of plan adaption. Conclusion: With an RTT-only, CT-based online adaptive SBRT workflow for A-P LN oligometastases, using a library of plans, 78% of the patients was treated with adaptive radiotherapy. This workflow enabled an iso-toxically delivered mean GTV BED 10 5 Gy dose increase and offers a chance of better oncological outcomes.

Keywords: Online adaptive, dose increase, oligometastases References:

1. Papalazarou C, Klop GJ, Milder MTW, Marijnissen JPA, Gupta V, Heijmen BJM, Nuyttens JJME, Hoogeman MS. CyberKnife with integrated CT-on-rails: System description and first clinical application for pancreas SBRT. Med Phys. 2017 Sep;44(9):4816-4827.

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Digital Poster Clinical and Dosimetric Insights from the First 100 Patients Treated with CBCT-based Online Adaptive Radiotherapy: A Single-Institution Evaluation Saib Rinnawi 1 , Kynann P. Aninditha 1 , Tarek E. Ellethy 1 , Stephan Baumbach 1 , Nora Tremmel 2 , Jannis Herkommer 2 , Nils Wegner 2 , Marc Münter 1 1 Department of Radiation Oncology, Klinikum Stuttgart, Stuttgart, Germany. 2 Department of Medical Physics and Radiation Protection, Klinikum Stuttgart, Stuttgart, Germany Purpose/Objective: Online adaptive radiotherapy (oART) allows daily adjustments to treatment plans based on the patient’s current anatomy, improving precision and reducing toxicity through advanced workflows [1,2]. The evolution of CBCT-based ART systems, such as the Varian Ethos®, has made online plan adaptation more effective, precise, and feasible within a short timeframe [2]. This retrospective study evaluates clinical and dosimetric outcomes of the first 100 patients with various cancer sites treated with oART using the Varian Ethos® system at Klinikum Stuttgart, Germany. The aim was to assess daily online plan adaptation, optimized to the patient’s anatomy of the day, compared to the scheduled plan, representing the initial reference plan rigidly recalculated on the day’s anatomy. Material/Methods: Between 02/2022 and 07/2023, 100 patients at Klinikum Stuttgart underwent oART using the Varian Ethos® system for various malignancies. Plan comparison metrics included PTV coverage (D98%) and doses to organs-at-risk (OARs). Toxicity data were collected during follow-up.