ESTRO 2025 - Abstract Book

S1518

Clinical – Mixed sites & palliation

ESTRO 2025

Results: Among 103 lesions treated in 100 patients, three patients had two lesions irradiated, including one case of simultaneous bilateral adrenal gland irradiation. Lesions were located in the head and neck (n=7), pelvis (n=71), lung (n=14), mediastinum (n=1), upper abdomen (n=7), and spine (n=3). Among them, 13 cases were treated using an SBRT concept. Treatment techniques included equidistant IMRT fields with 12 fields in 37 cases, 9 fields in 59 cases, and 7 fields lateral IMRT in 6 cases for lesions with laterality. A total of 2,392 adaptive fractions were delivered. Adaptive plans were selected in 98.3% of fractions. Median session time was 26:17 minutes, with complex cases such as cervix treatments requiring 35:04 minutes, compared to 23:07 minutes for prostate cases. Significant PTV coverage improvements were observed across all sites. For prostate cancer, D98% improved from 81.79% to 97.09% (p < 0.0001), and for cervical cancer, from 84.16% to 97.77% (p < 0.0001). OAR doses were generally reduced, particularly rectal and bladder doses in pelvic cases. For instance, rectal Dmean decreased by 0.85% per fraction (p < 0.0001), while bladder Dmean dropped by 0.42% per fraction (p < 0.0001). Follow- up data (median 12 months) revealed no grade ≥3 toxicities. Conclusion: CBCT-guided oART using the Varian Ethos® system demonstrates significant dosimetric advantages, improved target coverage, and comparable toxicity profiles across tumor sites. This single-institution evaluation highlights the feasibility of integrating oART into routine workflows, advancing personalized radiotherapy. References: 1. Glide-Hurst, C. K., Hackett, C., Kunz, J. M., Kumaraswamy, L., Price, R., Sattarivand, M., ... & Michalski, J. M. (2021). Adaptive radiation therapy (ART) strategies and technical considerations: A state of the ART review from NRG Oncology. International Journal of Radiation Oncology, Biology, Physics, 109 (4), 1054 – 1075. https://doi.org/10.1016/j.ijrobp.2020.11.048 2. Byrne, M., Archibald-Heeren, B., Hu, Y., Teh, A., Bertholet, J., & Foroudi, F. (2022). Varian Ethos online adaptive radiotherapy for prostate cancer: Early results of contouring accuracy, treatment plan quality, and treatment time. Journal of Applied Clinical Medical Physics, 23 (2), e13479. https://doi.org/10.1002/acm2.13479 Digital Poster Online adaptive palliative radiotherapy on a standard linac without a dedicated planning CT – first experiences from the Rapid Care trial Rune S Thing 1,2 , Charlotte Kristiansen 1,2 , Christine V Madsen 1,2 , Martin Berg 1,2 , Mette S Svenson 1,2 , Lars U Fokdal 1,2 1 Dept of Oncology, Vejle Hospital, University Hospital of Southern Denmark, Vejle, Denmark. 2 Radiotherapy Research Team, Vejle Hospital, University Hospital of Southern Denmark, Vejle, Denmark Purpose/Objective: Patients referred for palliative radiotherapy (RT) are often frail and in pain. The aim of the Rapid Care phase II trial is to reduce the total time that patients with bone metastases spend in the hospital for the consultation, treatment preparation and delivery of the first RT fraction. The protocol is planned to enroll 30 patients, to assess the feasibility of providing online adaptive RT (oART) on a standard linac without using a dedicated planning CT. Moreover, patient and staff satisfaction will be recorded and evaluated. Keywords: Online adaptive CBCT-guided radiotherapy 2414