ESTRO 2025 - Abstract Book

S3683

Physics - Quality assurance and auditing

ESTRO 2025

Conclusion: This study underscores the critical role of quality assurance (QA) in ensuring compliance with contouring and dosimetric protocols for spinal SBRT. Future spine SBRT trials should emphasize RT-QA on contouring target volumes and critical OARs, correlating deviations with outcomes.

Keywords: Quality Assurance, Spinal metastasis, SBRT

References: Guckenberger M, Billiet C, Schnell D, Franzese C , Spałek M, Rogers S, Stelmes JJ, Aebersold DM, Hemmatazad H, Zimmermann F , Zimmer J, Zilli T, Bruni A, Baumert BG, Nägler F, Gut P, Förster R, Madani I. Dose-intensified stereotactic body radiotherapy for painful vertebral metastases: A randomized phase 3 trial .Cancer. 2024 Aug 1;130(15):2713-2722. doi: 10.1002/cncr.35310.

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Mini-Oral First validation/commissioning of the novel RapidArc Dynamic technique for breast radiotherapy Truus Reynders 1 , Wout Piot 1 , Karel Aerts 1 , Bianca Vanstraelen 1 , Laurence Delombaerde 1,2 , Tom Depuydt 1,2 , Wouter Crijns 1,2 1 Radiation Oncology, University Hospitals Leuven, Leuven, Belgium. 2 Laboratory of Experimental Radiotherapy, KU Leuven, Leuven, Belgium Purpose/Objective: A new hybrid intensity modulated treatment delivery technique has been presented by Varian Medical Systems: RapidArc Dynamic (RAD) where the VMAT gantry rotation can be paused to deliver static IMRT fields. During treatment delivery collimator rotation is allowed. These hybrid treatments are optimized in a single step allowing for a reduction of OAR doses. We report the first clinical commissioning of these complex RAD plans – combining motion of gantry, leaf and collimator, with an increased gantry speed. Material/Methods: 10 left-sided breast cancer patients were retrospectively planned with RAD in Eclipse 18.1 with dose prescription 15x2.67Gy (whole breast) and 3.2Gy (SIB to the tumor bed) with energy 6X-FFF. Dose calculation algorithm ACUROS 18.1 and photon optimizer algorithm 18.1 were used. Plans consisted of a dynamic VMAT arc with two static IMRT angles (called ports) at tangential angles (and an avoidance sector to avoid dose to the lungs) (figure 1). A second VMAT arc with fixed collimator was added to deliver the boost dose. Plans were recalculated on the “Cheese” phantom (Standard Imaging Inc.) and delivered on a TrueBeam linac (v4.1). Two phantom orientations (0° and 90°) were applied to expose EBT3 films (Ashland Inc.) in the coronal and sagittal plane (figure 2). Ionization chamber measurements (A1SL, Standard Imaging Inc.) were acquired at two positions in the phantom per orientation. At least 48-hours post-irradiation, films were converted to dose using a triple-channel algorithm 1,2 and compared to the TPS dose in MyQA (IBA) with gamma criterion 3%/2mm(local) and 2%/2mm(local) with 10% low-dose threshold. No scaling of the film dose was performed. The beam-on time was measured during treatment plan delivery.