S2713
RTT - Patient preparation, immobilisation, and verification protocols
ESTRO 2026
abdominal tumors, potentially allowing for reduced ITV margins and improved therapeutic ratios. Keywords: SBRT, immobilization
compared to a historical cohort. Material/Methods:
A prospective, non-randomized, single-center, non- inferiority study was initiated in February 2025. 41 thoracic or abdominal tumors were eligible for SBRT will be enrolled and immobilized with the SBRT-HRC device during 4D-CT (Computed Tomography) simulation and treatment delivery in collaboration with SIHO®. The primary endpoint is the quantification of tumor displacement in the superior- inferior (SI), anterior-posterior (AP), and lateral (LAT) axes, measured on the 4D-CT. These data are compared against a historical cohort of patients treated with a thermoplastic mask immobilization systembetween 2018-2024. Secondary endpoints include acute and chronic toxicity (CTCAE v4.0), patient-reported comfort, and technician usability. Statistical analysis was performed using Student's t- test with a significance level of p<0.05.
Proffered Paper 1711 MRI-based quantification of respiratory motion reduction under non-invasive mechanical ventilation (NIMV) for ion-beam therapy in the abdomen Martin Paier 1 , Ariadna Cherit Hernández 1,2 , Stefan Wampl 3 , Ingo Albrecht Schmidt 4 , Martin Meyerspeer 4 , Michael Parkes 5,6 , Christian Ramsl 7 , Florian Watzinger 2 , Arjan Bel 5,6 , Irma van Dijk 5,6 , Piero Fossati 1,2 , Dietmar Georg 8 , Markus Stock 1,2 1 Department of Medical Physics, MedAustron, Ion Beam Therapy Center, Wr. Neustadt, Austria. 2 Division of Medical Physics, Karl Landsteiner Private University for Health Sciences, Krems, Austria. 3 Department of Medicine III, Division of Endocrinology and Metabolism, High Field MR Center, Medical University of Vienna, Vienna, Austria. 4 Center for Medical Physics and Biomedical Engineering, High Field MR Center, Medical University of Vienna, Vienna, Austria. 5 Department of Radiation Oncology, Amsterdam UMC Location University of Amsterdam, Amsterdam, Netherlands. 6 Treatment and Quality of Life, Cancer Biology and Immunology, Cancer Center Amsterdam, Amsterdam, Netherlands. 7 Department of Physics, Technical University of Vienna, Vienna, Austria. 8 Division of Medical Radiation Physics, Department of Radiation Oncology, Medical University of Vienna, Vienna, Austria Purpose/Objective: Respiratory motion is a major source of uncertainty in ion-beam radiotherapy. Non-invasive mechanical ventilation (NIMV) may standardise breathing patterns and reduce both organ motion and its variability. This pilot study with healthy volunteers investigated the feasibility of NIMV with and without an immobilisation (immo) mask and quantified its effect on abdominal organ motion amplitude and variability during NIMV2 (at 2 breaths per minute - brpm) and at NIMV60 (at 60 brpm with positive end expiratory pressure - PEEP) via MRI. Material/Methods: Ten healthy volunteers (approved by ethics committee – approval number: 1103/2024) underwent two MRI sessions on a 3T wide-bore scanner (Philips Ingenia). A Hamilton MR1 ventilator delivered two breathing modes to fully conscious and unmedicated participants via a face mask: NIMV2 and NIMV60 with 15cmH2O of PEEP, which were compared to free breathing (FB). MR imaging used a balanced fast field-
Results: Between February to August 2025, 32 patients (41 lesions) have been included in the experimental arm, and 32 patients (40 lesions) in the historical control arm. Patient characteristics were well-balanced between both cohorts, with a predominance of lung tumors (n=23 vs n=22). The SBRT-HRC device demonstrated a marked reduction in tumor motion across all axes. The mean displacement in the experimental arm compared to control arm was 0.1 (LAT) vs 0.74 cm (p=0,02), 0.2 (AP) vs 0.84 cm (p=0.02), and 0.3 (SI) vs 0.5 cm (p=0.01), respectively. Patient- reported comfort with the SBRT-HRC was high, with a mean score of 8.73 (on a scale of -6 to 15, where higher is better). RTT usability was rated favorably with a mean score of 6.0 (on a scale of -12 to 12). No unexpected toxicities related to the device were observed. Conclusion: In this interim analysis, the novel SBRT-HRC immobilization system demonstrates superior tumor motion control in all three dimensions compared to a standard immobilization technique. The device is well- tolerated by patients and well-regarded by RTTs o therapists. The SBRT-HRC is a promising tool to enhance the precision of SBRT for thoracic and
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