ESTRO 2025 - Abstract Book

S3113

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2025

Tomography in 6 Seconds: A Patient Study of Comparative Image Quality, International Journal of Radiation Oncology*Biology*Physics 108 (2020) 253-262. 3. M. Held, F. Cremers, P.J. Sneed, S. Braunstein, J. Morin, A. Slotman, C.F. Behrens, Technical note: Phantom-based evaluation of CBCT dose calculation accuracy for use in adaptive radiotherapy, Journal of Applied Clinical Medical Physics 17 (2016) 390-395.

1787

Digital Poster An automated workflow for daily CT image-guided online adaptive liver SBRT with carbon ions Rita Pestana 1,2,3 , Sebastian Regnery 1,2,3 , Thomas Mielke 2 , Jakob Liermann 1,3 , Cedric Beyer 1,2,3 , Jürgen Debus 1,2,3 , Sebastian Klüter 1,3 , Katharina Seidensaal 1,2,3 , Julia Bauer 1,2,3 1 Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg, Germany. 2 Heidelberg Ion beam Therapy Center (HIT), Heidelberg University Hospital, Heidelberg, Germany. 3 Heidelberg Institute for Radiation Oncology (HIRO), National Center for Radiation Research in Oncology (NCRO), Heidelberg, Germany Purpose/Objective: Carbon ion radiotherapy (CIRT) is highly beneficial for hepatocellular carcinoma (HCC) patients. The dose prescription is typically delivered in four fractions, requiring high geometrical precision. At the Heidelberg Ion-Beam Therapy Center (HIT), image-guidance is provided by in-room CT imaging at the isocentre. We present a new automated online-adaptive carbon ion liver stereotactic body radiotherapy (SBRT) pipeline to treat HCC lesions. This workflow was retrospectively tested on liver SBRT patients treated at HIT. Material/Methods: A cohort of 13 patients with a total of 14 HCC lesions was considered, with 4 x 10.5 Gy(RBE) CIRT and daily in-room CT imaging before each fraction. We developed an automated pipeline in a research version of RayStation 11B to map the contours on the daily CT with deformable image registration (DIR) and replan the treatment on this image. For six patients (group A), the DIR contours on the daily CT were compared to those manually contoured; the automatically adapted plans were validated against plans designed by an experienced dosimetrist. For the remaining eight cases (group B), the contours were deformably mapped from the planning to the daily CT and then adjusted within PTV + 3 cm by a radiation oncologist. This was done to evaluate the time required for this step and thus the clinical feasibility of the workflow. Results: For group A, the mean distances to agreement (MDA) achieved with DIR are below 3 mm for all the structures apart from the stomach (Figure 1). The time needed to adjust the deformed contours on group B within PTV + 3 cm ranged between 41 seconds and 10 minutes. The daily plan optimization took up to 4 minutes and a maximum of 4 minutes were needed to obtain the final dose, including the scaling to the primary prescription with a variable RBE model. The dosimetric outcomes of the automated plans are in accordance with those manually adapted (Figure 2).