S2178
Physics - Inter-fraction motion management and daily adaptive radiotherapy
ESTRO 2026
Oncology Biology Physics 122 (4) 2025, 838-864. Keywords: online adaptive radiotherapy, FMEA, oART plan QA
Scripting functionality within the TPS was used for further automation and efficiency of the workflow as well as enabling safety checks to be embedded at different stages including: initial pre-adaptive checks to confirm details about the upcoming workflow including patient and prescription details; adaptive plan QA checks to ensure the oART treatment plan is safe to deliver; plan transfer checks to ensure the correct oART plan is delivered by checking all plan parameters sent to the unit agree with those in the TPS. FMEAs were utilised to determine required workflow safety checks and mitigation [2, 3]. After the oART treatment plan has been generated, the oART plan or non-adaptive scheduled plan can be selected for treatment. An overview of the online workflow is shown in Figure 1. Results: The Radixact-RayStation oART workflow has been used clinically since March 2025 to treat post-operative endometrial cancer patients prescribed 45 Gy in 25 fractions. To date, 23 patients have had at least one oART fraction and a total of 276 adaptive sessions have been delivered, with the oART plan being clinically preferred and selected in all but one occasion (>99.5%). The implemented safety checks have highlighted issues that were corrected within the workflow, including small and erroneous target contours. Conclusion: The workflow presented here represents the world’s first oART process using the Radixact treatment platform with the RayStation TPS. We have shown that safe oART can be performed with pre-existing software and hardware which we believe will be crucial for widespread oART adoption. The presented workflow will next be extended for additional clinical indications. Furthermore, by developing oART using independent software, the workflow can be easily transferred to multiple treatment platforms, enabling the transition towards a true modern radiotherapy department where oART will become standard. References: [1] Tegtmeier RC. Et al. Characterization of imaging performance of a novel helical kVCT for use in image - guided and adaptive radiotherapy. Journal of Applied Clinical Medical Physics 23 (6) 2022.[2] Osman S et al. Identifying high-risk components in online adaptive RT through a multi-centre FMEA to address clinical trial QA needs. Radiotherapy and Oncology 206: S3656-S3658[3] Chetty IJ., et al. Quality and Safety Considerations for Adaptive Radiation Therapy: An ASTRO White Paper. International Journal of Radiation
Digital Poster 4269 Dosimetric and Volumetric Evaluation of Daily Adaptive Radiotherapy in Rectal Cancer Francisco Camba 1 , Ismael Sancho 1 , Daniel Lambisto 1 , Rodolfo De Blas 1 , Sandra Barbero 1 , Olalla Santa-Cruz 2 , Leyre Asiaín 2 , Eva Ferrer 2 , Rebeca Rodríguez 2 , Francesco Amorelli 2 , Llorenç Benaches 1 , Álvaro Peña 1 , Cristina Picón 1 1 Medical Physics and Radiological Protection, Catalan Institution of Oncology (ICO), Barcelona, Spain. 2 Oncology Radiotherapy, Catalan Institution of Oncology (ICO), Barcelona, Spain Purpose/Objective: To evaluate the clinical feasibility and dosimetric performance of daily adaptive radiotherapy (ART) for rectal cancer using the Varian Ethos system. Specifically, the analysis aimed to quantify differences in target coverage and in doses to organs of interest (OIs) between scheduled and adapted treatment plans, and to assess potential anatomical and volumetric changes throughout the treatment course. Material/Methods: A total of 200 treatment sessions from 8 rectal cancer patients treated with daily ART were retrospectively analyzed. Prescribed doses were 45 Gy for PTV1 (elective region) and 50 Gy for PTV11 (tumor boost). For each session, two plans were compared: the Scheduled plan, corresponding to the reference plan recalculated on the daily CBCT, and the Adapted plan, a new plan generated from this daily CBCT image.Dosimetric parameters included CTV1 and CTV11 (V95%, D95%, D99%), PTV1 and PTV11 (V95%, D95%, D99%, and Paddick conformity index), and OIs: bladder (V15 Gy, V40 Gy, D0.03 cc) and small bowel (V15 Gy, V45 Gy, D0.03 cc). Differences between plans were analyzed using the Wilcoxon test ( α = 0.05) and represented with boxplots. Variations in target volumes were assessed by comparing the first session with the mean of the last five. The average treatment time per session was also recorded. Results: Adapted plans achieved notably improved target coverage for both CTV and PTV volumes, with statistically significant differences in D99% and V95% (p < 0.05). The Paddick conformity index was substantially higher in the adapted plans, with statistically significant differences compared to the scheduled plans, indicating a more conformal dose distribution around the target volumes. For OIs, differences were less pronounced, showing a trend
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