S1677
Physics - Detectors, dose measurement and phantoms
ESTRO 2026
10×10 cm² static fields were calculated at multiple gantry angles using AAA/AXB (Eclipse) and CC/MC (Monaco), with two dose grid resolutions per detector (Evolution: 0.1/0.762 cm; Resolution: 0.1/0.65 cm). Five 6 MV VMAT plans were also recalculated using AXB and MC. All distributions were measured with and without angular correction and evaluated using 2%/2 mm – 5% threshold gamma analysis, enabling assessment of the effects of HU correction, angular dependence, grid resolution, and algorithm selection on PSQA performance. Results: For both static fields and VMAT plans, applying HU correction improved gamma agreement across all algorithms. When all corrections were disabled, AAA showed the least sensitivity, whereas CC and MC were more affected by detector response and angular variations. Increasing the TPS dose grid resolution reduced the magnitude and variability of correction- related changes, indicating that finer spatial resolution stabilizes PSQA outcomes. In static fields, the gantry angle correction had minimal effect for AAA/AXB, but reduced agreement for CC/MC. In contrast, during VMAT delivery, these angular dependencies reversed, with AXB and MC showing recovery in agreement across gantry rotation. Additionally, for VMAT, higher spatial resolution reduced the standard deviation between repeated measurements, while lower resolution increased the contribution of the DTA component in gamma evaluation. Conclusion: Reliable gamma evaluation requires accurate modeling of the detector’s high-density materials, though the impact of HU correction decreases with finer TPS dose grid resolution. AAA was least, and MC most, sensitive to the absence of HU correction, reflecting differences in heterogeneity handling. Gantry angle effects were algorithm-dependent; MC showed a negative angular correction impact in static fields, which reversed to a positive effect in VMAT. Higher dose resolution stabilized measurements by reducing variability, while lower resolution increased the influence of the DTA component in gamma evaluation. Keywords: Electron density, Gamma index, Angular Correction Digital Poster Highlight 4059 Towards harmonized clinical practice in radiochromic film dosimetry – EBT-4 calibration analysis and error estimation within an open- source platform Nicola Zancopè 1 , Samuele Cavinato 2 , Riccardo Lombardi 1 , Angelo Giannone 2 , Marta Paiusco 2 , Alessandro Scaggion 2
Conclusion: In the 2D patient specific alert systems, it is important to apply various metrics in the analysis rather than to be limited to a single metric, such as the Gamma Passing Rate. In this contribution, we will show that using a combination of metrics, and not merely the widely applied gamma-index analysis, is important to detect serious treatment errors and to estimate the error source, thereby enhancing patient safety. References: [1] Dogan N., Mijnheer B.J., Padgett K., et al., AAPM Task Group Report 307: Use of EPIDs for Patient- Specific IMRT and VMAT QA, Medical Physics. 50, e865– e903 (2023)[2] Miften, M, et al. Tolerance limits and methodologies for IMRT measurement ‑ based verification QA: recommendations of AAPM Task Group No. 218. Medical Physics, 45.4: e53-e83 (2018). Keywords: Transit dosimetry, Deep Learning, Analysis metrics Effect of Detector Electron-Density and Angular- Response Corrections in 2D Arrays on Gamma Evaluation of Plans with Varying Voxel Sizes and Algorithms Oğuzhan Ayrancı 1 , Cemile Ceylan 2,3 1 Radiation Oncology, Tinaztepe university, Izmir, Turkey. 2 Radiation Oncology, Istanbul Oncology Hospital, Istanbul, Turkey. 3 Faculty of Health Sciences, Yeditepe University, Istanbul, Turkey Purpose/Objective: This study evaluates the effects of HU correction, angular dependence correction, and dose grid resolution on gamma results for two 2D detector systems, and compares these effects across multiple TPS dose calculation algorithms. The goal is to determine how these factors influence PSQA accuracy and to clarify the conditions that improve reliability in clinical practice Material/Methods: Two 2D ion-chamber arrays (IBA MatriXX Evolution and Resolution) were scanned with their miniPhantom adapters using 1-mm CT and imported into Eclipse (v16.1) and Monaco. Couch settings were applied, detector regions were contoured, and HU-corrected and uncorrected CT datasets were created. 6 MV, Digital Poster 3999
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