S2112
Physics - Inter-fraction motion management and daily adaptive radiotherapy
ESTRO 2026
Digital Poster Highlight 790
Towards a shuttle-based workflow for daily online MRI-guided particle therapy: organ variability and anatomical robustness in the female pelvis Friderike K. Longarino 1,2 , Danae Droutsas 2,3 , Lars Wessel 2,4 , Cedric Beyer 2,4 , Rita Pestana 2,4 , Julia Bauer 2,5 , Katharina Seidensaal 2,4 , Jürgen Debus 2,4 , Sebastian Klüter 2,4 , Nathalie Arians 2,4 1 Clinical Cooperation Unit Translational Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany. 2 Department of Radiation Oncology and Heidelberg Ion Beam Therapy Center, Heidelberg University Hospital, Heidelberg, Germany. 3 Faculty of Physics and Astronomy, Heidelberg University, Heidelberg, Germany. 4 Heidelberg Institute for Radiation Oncology (HIRO), National Center for Radiation Research in Oncology (NCRO), Heidelberg, Germany. 5 Department of Radiation Oncology, Charité - Universitätsmedizin Berlin, Berlin, Germany Purpose/Objective: Online adaptive particle therapy can take into account anatomical changes during treatment [1,2]. In a shuttle-based daily online MRI-guided strategy, patients remain immobilized in the treatment position during transfer between MRI and irradiation, while high soft tissue contrast imaging is obtained. This study investigated organ variability during shuttle transfers with our current uterine cervical and endometrial cancer immobilization set-up [3], with the goal of applying the workflow for MRI-guided particle therapy for gynecological malignancies. Material/Methods: Twenty healthy female volunteers (18–55 years old) underwent a series of four MRI scans in a 1.5 T MRI scanner using a 3D T1 GRE sequence, interspersed with a waiting period and intra-hospital transport simulations. To control for physiological effects that can cause cervical motion (i.e., bladder and rectal filling), and to simulate clinical conditions with a full bladder, participants followed a standardized drinking and fasting protocol prior to MRI acquisition. The study comprised (Figure 1): volunteer positioning on an indexed knee and foot support fixed to a transfer table, MRI 1 (baseline MRI), 10-minute waiting period as a time control phase, MRI 2, short transport of 5 minutes, MRI 3, long transport of 10 minutes, and MRI 4. In each MRI set, the external, cervix, uterus, bladder, peritoneal cavity with the intestine, and rectum were contoured. To quantify organ displacement, Dice similarity coefficients (DSC) and mean distances to agreement (MDA) were calculated for shifts between consecutive image sets and throughout the study.
Conclusion: BH in lung SBRT showed several millimeters of variation between simulation and treatment. BH reproducibility did not correlate significantly with demographic or clinical factors. However, reproducibility was consistent (i.e. correlated) across treatment fractions. References: 1. Peng Y, Vedam S, Chang JY, et al: Implementation of feedback-guided voluntary breath-hold gating for cone beam CT-based stereotactic body radiotherapy. Int J Radiat Oncol Biol Phys 80:909-17, 2011 Keywords: Lung SBRT, Breath-hold reproducibility
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