ESTRO 2025 - Abstract Book

S2638

Physics - Detectors, dose measurement and phantoms

ESTRO 2025

Keywords: beam quality, particle therapy ,dosimetry

References: [1] Weyrather, W. K., & Debus, J. (2003). Particle beams for cancer therapy., doi:10.1053/clon.2002.0185. [2] INTERNATIONAL ATOMIC ENERGY AGENCY (2024). Absorbed Dose Determination in External Beam Radiotherapy, Technical Reports Series No.398 (Rev. 1), Vienna. [3] Urago, Y. et al. (2023). Monte Carlo-calculated beam quality and perturbation correction factors validated against experiments for Farmer and Markus type ionization chambers in therapeutic carbon-ion beams. Physics in Medicine and Biology, doi:10.1088/1361-6560/acf024. [4] Holm, K. et al. (2022). Direct determination of kQ for Farmer-type ionization chambers in a clinical scanned carbon-ion beam using water calorimetry. Physics in Medicine & Biology, doi:10.1088/1361-6560/ac4fa0.

3588

Proffered Paper Large multicentre intercomparison of small field dosimetry using a new plastic scintillator detector Serenella Russo 1 , Francesca Romana Giglioli 2 , Antonella Bianculli 3 , Marta Casati 4 , Stefania Cora 5 , David Fedele 6 , Marco Fusella 7 , Stefano Giancaterino 8 , Maria Antonietta Gilio 9 , Anna Ianiro 10 , Stefania Linsalata 11 , Emilio Mezzenga 12 , Eugenia Moretti 13 , Veronica Richetto 2 , Stefano Riga 14 , Michela Sabetti 15 , Anna Sardo 16 , Gianluca Segata 17 , Cinzia Talamonti 4,18 , Pietro Mancosu 19 1 Medical Physics Unit Florence, AUSL Toscana Centro, Florence, Italy. 2 Medical Physics Unit, A.O.U. Città della Salute e della Scienza di Torino, Turin, Italy. 3 Medical Physics Dept., IRCCS-CROB, Rionero in Vulture (PZ), Italy. 4 Medical Physics Unit, Azienda Ospedaliero Universitaria Careggi, Florence, Italy. 5 Medical Physics Unit, Ospedale San Bortolo, AULSS8 Berica, Vicenza, Italy. 6 Medical Physics Unit Pistoia Prato, AUSL Toscana Centro, Pistoia, Italy. 7 Radiation Oncology Department, Policlinico Abano Terme, Abano Terme (PD), Italy. 8 Dipartimento di Radioterapia, Università di Chieti, Chieti, Italy. 9 Medical Physics Unit, Azienda Toscana Nord Ovest, Lucca, Italy. 10 Medical Physics Department, IRCCS Regina Elena National Cancer Institute - IFO, Rome, Italy. 11 Medical Physics Unit, Pisa University Hospital, Pisa, Italy. 12 Medical Physics Unit, IRCCS IRST Dino Amadori, Meldola (FC), Italy. 13 Medical Physics Unit, ASUFC, Udine, Italy. 14 Medical Physics Unit, ASST Spedali Civili, Brescia, Italy. 15 Medical Physics Unit, AULSS2 Marca Trevigiana, Treviso, Italy. 16 Medical Physics Unit, ASLCN2, Verduno (CN), Italy. 17 Tecnosan S.r.l., Società Benefit, Trento, Italy. 18 DSBSC, University of Florence, Florence, Italy. 19 Medical Physics Unit, IRCCS Humanitas Research Hospital, Rozzano (MI), Italy Purpose/Objective: Small field dosimetry remains challenging, even in the era of “golden data” for linac commissioning. This study aimed to provide benchmark data for small field measurements within a national context, utilizing a standardized protocol and state-of-the-art detector, adopting a crowd-knowledge-based approach. Material/Methods: Thirty-five centers with modern linacs from various vendors participated in this study. Field output factors (FOFs) were measured for square fields (0.5–5 cm) and equivalent field sizes (EFS) for "very small" fields (0.5–3 cm) using the Exradin W2 plastic scintillator detector (Standard Imaging SI) in parallel configuration. The W2 dosimeter was paired with a MAX SD electrometer to correct Cerenkov Light Ratio values, enabling both point and scan measurements in a 3D water phantom. Fields were created using jaws aligned with MLC apertures and normalized to 10×10 cm². Measurements were conducted at 10 cm depth in water with an SSD of 90 cm. The experimental point errors were estimated accounting for the statistical dispersion of the repeated measurements and the positioning uncertainty.