S2401
Physics - Quality assurance and auditing
ESTRO 2026
2025b), motion amplitude deviation from known phantom settings, phase-consistency analysis (Velocity AI, v4.2, Varian) to assess the target volume and diameterdeviations from 3DCT, and Hounsfield Unit (HU) consistency. These tests (from [1-3])were applied to a set of six regular respiratory curves, three pseudo- irregular curvesobtained from the literature [1], and one irregular curve provided byVisionRT.
variations from set-up CBCT to post CBCT (N=25) Conclusion: The reported intrafraction prostate motion observed on post-treatment imaging remained within accepted limits, in spite of longer ‘on couch’ times. These findings support the feasibility of prostate SABR with a fast delivery on a conventional linac using pre- treatment CBCT imaging and SGRT intrafraction 1. van As N. Tree A. Patel J. et al. 5-Year Outcomes from PACE B: An International Phase III Randomized Controlled Trial Comparing SBRT vs. Conventionally Fractionated or Moderately Hypo Fractionated External Beam Radiotherapy for Localized Prostate Cancer. Int J Radiat Oncol Biol Phys. 2023;117(4):e2- e3. 2. Jackson W. Silva J. Hartman H et al. Stereotactic Body Radiation Therapy for Localized Prostate Cancer: A Systematic Review and Meta-Analysis of Over 6,000 Patients Treated On Prospective Studies. Int J Radiat Oncol Biol Phys. 2019;104(4):778-789. 3. di Franco F. BaudierT. PialatP. et al. Ultra-hypofractionated monitoring. References: prostate cancer radiotherapy: Dosimetric impact of real-time intrafraction prostate motion. Physicia Medica. 2024;118:103207. Keywords: Prostate, SABR, Intrafraction Digital Poster 4563 Establishing a QA program for 4D CT in lung SBRT using a dynamic thorax phantom Rita Nunes 1 , Joana Teixeira 2 , Carla Alves 2 , Sofia Silva 2 , Tiago Ventura 2 , Maria Carmo Lopes 2 1 Physics Department, University of Coimbra, Coimbra, Portugal. 2 Medical Physics Department, IPO Coimbra, Coimbra, Portugal Purpose/Objective: To establish a comprehensive QA framework to evaluate 4DCT acquisitions for lung SBRT treatments. Material/Methods: 4DCT acquisitions were performed on a Siemens Somatomgo.Sim scanner, with respiratory monitoring provided by SimRTsystemv7.2 (from VisionRT). QA tests were conducted using the CIRS Dynamic Thorax Phantom. Phantom motion, simulating both simple thoracic and tumor movement, was controlled via the Motion Control module.More complex and realistic motion patterns were imported from an external source. The QA programincluded functional and imaging- based tests(Table 1): respiratory monitoring, 4DCT Reconstruction and export to TPS, SimRTsynchronization (amplitude and period deviation analysis performed in MATLAB
Table14DCT quality assurance tests, grouped by type (functional and imaging-based), including tolerances for amplitude, period, volume, diameter, and HU values. Results: SimRT synchronization tests showed excellent agreement (correlation coefficient > 0.998) between programmed and recorded motions.For regular respiratory curves (emptycircles - Figure 1), all assessed parameters remained within the established tolerances defined for regular motion patterns, confirming the system’s reliability. In pseudo- irregular (full circles) and irregular curves (triangles), SimRT synchronization performed correctly, but increased deviations,were observed, particularly in volume(maximum of 105.7% for the 100Exp phase of irregular breathing pattern)but also inHU values (Figure 1).
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