S1697
Physics - Detectors, dose measurement and phantoms
ESTRO 2026
Physics Unit, ASLCN2, Verduno (CN), Italy. 21 Medical Physics Unit, AO San Giovanni Addolorata, Rome, Italy. 22 Medical Physics Unit, A.O.U. Maggiore della Carità, Novara, Italy. 23 DSBSC, University of Florence, Florence, Italy. 24 Dept. of Biomedical Sciences, Humanitas University, Pieve Emanuele, Milan, Italy Purpose/Objective: Accurate dosimetry and modelling of small radiation fields are essential for advanced radiotherapy techniques. The AIFM SBRT Working Group conducted a multicentre study to establish a consistent dataset for small field measurements using a standardized protocol and a new-generation detector. Each centre’s measurements were compared with commissioning data and treatment planning system (TPS) calculations. Material/Methods: Field output factors (FOFs) for square fields (0.5–5 cm) and equivalent field sizes (EFS, 0.5–3 cm) were measured in 27 Italian radiotherapy centres using the Standard Imaging Exradin W2 plastic scintillator detector with a MAX SD electrometer to correct for Cerenkov light. Measurements were performed in a 3D water phantom with an isocentric setup (SSD=90 cm, depth=10 cm) and an “SBRT-style” configuration, with jaws and MLCs matched to the selected field size [1]. Data were normalized to the 10 cm reference field. Uncertainty budgets included statistical dispersion and setup reproducibility. TPS calculations were performed under identical conditions (grid size 1mm3 for EFS≤1 cm) and compared with W2 results. Additional comparisons were made between W2 and routine clinical detectors. Results: Twenty centres used 6 MV-FFF and fourteen used 6 MV-FF beams. W2 data were highly consistent across centres, with deviations within 1.5% for EFS ≥ 1 cm and about 5% for 0.5 cm (Fig.1). Larger discrepancies (>5% for 1 cm EFS) were observed for one specific LINAC model. Fig1: Relative deviations among all involved centers for EFS and FOF W2 measurements Combined uncertainties ranged from 0.7–1.7% (1–5 cm) and remained below 3% for 0.5 cm fields. TPS results agreed well with W2 measurements (median ratio 0.99 ± 0.02). For 1cm EFS the maximum difference was 2.7%. The largest deviation (22%) occurred for 0.5 cm EFS, a field size not included in any centre’s TPS beam commissioning. Similar trends were found for both beam energies. Routine detectors also yielded slightly lower FOFs than W2 for very small fields (median ratio 0.99 ± 0.02), with no data available for 0.5 cm fields.
[1] L. H.G. van der Pol et al. Analyzing Cardiorespiratory Motion and Its Dosimetric Effect on Stereotactic Arrhythmia Radio-Ablation: A STOPSTORM.eu Consortium Study. International Journal of Radiation Oncology, Biology, Physics. 2025. doi: 10.1016/j.ijrobp.2025.09.039[2] P. Dvorak.Clinical Radiotherapy Physics with MATLAB: A Problem-Solving Approach. Chapter 7: Dose Calculation. CRC Press, 2018doi: 10.1201/9780429508097[3] T. Bortfeld et al. Effects of motion on the total dose distribution.Seminars in Radiation Oncology, Vol. 14 (1), pages 41-51, 2004. doi: 10.1053/j.semradonc.2003.10.011. Keywords: radioablation, arrhythmia, CyberKnife Digital Poster 4814 Multicentre Assessment of Small Field Dosimetry Using a Plastic Scintillator Detector in SBRT Application Serenella Russo 1 , Francesca Romana Giglioli 2 , Antonietta Bartoli 3 , Marta Casati 4 , Stefania Cora 5 , David Fedele 6 , Marco Fusella 7 , Alfredo Gambirasio 8 , Chiara Gasperi 9 , Maria Antonietta Gilio 10 , Stefania Linsalata 11 , Carmelo Marino 12 , Tiziana Malatesta 13 , Edoardo Mastella 14 , Emilio Mezzenga 15 , Eugenia Moretti 16 , Anna Radice 17 , Veronica Richetto 2 , Stefano Riga 18 , Michela Sabetti 19 , Anna Sardo 20 , Antonella Stravato 21 , Luca Vigna 22 , Cinzia Talamonti 23 , Pietro Mancosu 24 1 Medical Physics Unit Florence-Empoli, Department of Hospitals Network, Azienda USL Toscana Centro, Florence, Italy. 2 Medical Physics Unit, DA.O.U. Città della Salute e della Scienza di Torino, Turin, Italy. 3 Medical Physics Unit, Azienda USL Toscana Sud Est, Grosseto, Italy. 4 Medical Physics Unit, AOU Careggi, Florence, Italy. 5 Medical Physics Unit, Ospedale San Bortolo, AULSS8 Berica, Verona, Italy. 6 Medical Physics Unit Prato-Pistoia, Department of Hospitals Network, Azienda USL Toscana Centro, Pistoia, Italy. 7 Radiation Oncology Department, Policlinico Abano Terme, Abano Terme, Italy. 8 Medical Physics Unit, Humanitas Gavazzeni, Bergamo, Italy. 9 Medical Physics Unit, AUSL Toscana Sud Est, Arezzo, Italy. 10 Medical Physics Unit, Azienda Toscana Nord Ovest, Lucca, Italy. 11 Medical Physics Unit, Pisa University Hospital, Pisa, Italy. 12 Medical Physics Unit, ICC Humanitas, Catania, Italy. 13 Medical Physics Unit, Isola Tiberina - Gemelli Hospital, Rome, Italy. 14 Medical Physics Unit, , A. O. U. Ferrara, Ferrara, Italy. 15 Medical Physics Unit, IRCCS Istituto Romagnolo per lo Studio dei Tumori (IRST) “Dino Amadori”, Meldola (FC), Italy. 16 Medical Physics Unit, ASUFC, Udine, Italy. 17 Medical Physics Unit, ASST Cremona, Cremona, Italy. 18 Medical Physics Unit, ASST Spedali Civili, Brescia, Italy. 19 Medical Physics Unit, AULSS2 Marca Trevigiana, Treviso, Italy. 20 Medical
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