ESTRO 2024 - Abstract Book

S4134

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2024

33

Digital Poster

Updated results of intrafractional motion detection for spine SBRT via stereoscopic X-ray imaging

Johannes Mücke 1 , Lili Huang 1 , Vanessa da Silva Mendes 1 , Guillaume Landry 1 , Michael Reiner 1 , Claus Belka 1 , Philipp Freislederer 2 , Maximilian Niyazi 3 , Stefanie Corradini 1 1 University Hospital, LMU Munich, Radiation Oncology, Munich, Germany. 2 Brainlab AG, Radiation Oncology, Munich, Germany. 3 University Hospital, Tuebingen, Radiation Oncology, Tuebingen, Germany

Purpose/Objective:

Spine stereotactic body radiotherapy (SBRT) is becoming a standard of care for selected patients with spinal metastases. Particularly for patients with oligometastatic disease, SBRT can prolong progression-free survival by delivering high biologically effective doses (BED). Due to the close vicinity of critical structures, especially the spinal cord, standards for safety for spine SBRT should be high. Advanced image guidance and reliable patient immobilization are usually fundamental requirements. Immobilization is typically achieved with individualized vacuum body fixation. Patient setup and position verification on a conventional linear accelerator is usually achieved using cone beam computed tomography (CBCT) scans. During the treatment itself, the patient position is not typically monitored. However, recent technological developments have facilitated intrafractional motion detection with immediate correction of the patient positioning during each radiotherapy session. This study was conducted, to evaluate intrafractional motion during spine SBRT in patients without individualized immobilization using high precision patient monitoring via orthogonal X-ray imaging with the ExacTrac Dynamic (ETD) system. Intrafractional X-ray imaging data were collected from patients receiving spine SBRT. Treatment was carried out with 2-4 (median: 3) coplanar volumetric arc therapy (VMAT) single-arc beams. Fractionation schedules included 2x 9/12 Gy (PTV/SIB PTV), 3x 7/9 Gy and 5x 5/6 Gy with the maximum dose limited to 125 %. No individualized immobilization devices (e.g., vacuum cushions) were used during the treatment. Intrafractional motion was monitored using the ETD System (Brainlab AG, Munich, Germany). During the irradiation, stereoscopic X-ray images were acquired for each treatment arc at gantry positions 0°, 90°, 180° and 270° (monitoring X-rays). Additional X-rays were acquired between beams if the wait was long or after decision of the radiation therapist (verification X-rays). Based on the registration of these X-ray images to previously generated digitally reconstructed radiographs, the system automatically detected target deviations along six degrees of freedom (6 DOF). Tolerances for repositioning were 0.7 mm for the three translational and 0.5° for the three rotational axes. Patients were repositioned when the tolerance levels were exceeded. Assuming no positional corrections during the treatment, cumulative deviations were calculated over time for each individual fraction by summing the values of all X-rays that exceeded tolerance levels and resulted in a shift application. The maximum cumulative deviation (MCD) was calculated for all 6 DOFs by taking the largest deviation at any time during each individual fraction. Material/Methods:

Results: