ESTRO 2025 - Abstract Book

S3533

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTRO 2025

robust IMPT for head-and-neck cancer: A probabilistic uncertainty analysis of clinical plan evaluation with the Dutch model-based selection. Radiotherapy and Oncology , 186 , 109729. [2] Protonentherapie, L. P. (2021). Landelijk Platform Radiotherapie Gastroenterologische Tumoren (LPRGE). Addendum Slokdarmcarcinoom bij Landelijk Indicatie Protocol Protonentherapie Longcarcinoom .

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Digital Poster Evaluation of the proton range accuracy using Single and Dual Energy Computed Tomography Davide Alio 1 , Floriana Pansini 1 , Giuseppe Castiglione Minischetti 1 , Stefania Comi 1 , Marco Liotta 1 , Juan Antonio Vera Sanchez 2 , Daniela Alterio 3 , Barbara Alicja Jereczek-Fossa 3,4 , Federica Cattani 1 1 Division of Medical Physics, IEO European Institute of Oncology IRCCS, Milan, Italy. 2 Division of Medical Physics, Centro de Protonterapia Quironsalud, Madrid, Spain. 3 Division of Radiation Oncology, IEO European Institute of Oncology IRCCS, Milan, Italy. 4 Department of Oncology and Hemato-oncology, University of Milan, Milan, Italy Purpose/Objective: X-ray CT images are the standard for proton beam planning, but CT noise and the non-unique conversion of HU values to stopping power ratio (SPR) result in imperfect dose calculations and introduce density uncertainties[1]. Dual-Energy CT (DECT) scanners[2] offer new possibilities for improving SPR conversion accuracy compared to Single-Energy CT (SECT)[3]. Siemens Syngo.via software (version-VA40) provides a commercial solution for processing DE raw images, generating Monoenergetic Plus (Mono+) images and DirectSPR maps. This study evaluates the impact of HU-to-SPR conversion methods on the accuracy of proton range estimation in treatment planning system (TPS). Proton ranges derived from TPS dose calculations using SECT, Mono+75keV, and DirectSPR images were compared with experimental measurements. Material/Methods: Animal organ samples were irradiated using box-shaped dose distributions and the proton range was probed using a Zebra multi-layer ion chamber (IBA Dosimetry). SECT (120kVp) and DECT (80 and 140kVp) images were acquired for each sample, with DirectSPR and Mono+ images reconstructed using Syngo.via software. All images were imported into the Raystation TPS (version-12A) , and HU-to-SPR conversion curves for SECT and Mono+ images were obtained through CT Stoichiometric Calibration[4-5]. A Python script derived the integrated depth dose (IDD) from dose calculations, and measured and TPS-derived IDDs were analysed to extract the 90% distal depth (D 90% R), taken as the proton range estimator. Differences between measured and TPS-derived D 90% R values were calculated across image sets, and the average and standard deviation for three different measurement points determined. Density uncertainty for each sample was assessed as the ratio of the absolute difference from the measured range to sample thickness. Results: The results of the animal organ sample irradiations are summarized in Tab.1. TPS proton range values varied slightly across image sets, with Mono+75keV showing the best agreement for liver, heart, and bone measurements; DirectSPR performing best for kidney; and SECT for muscle. Overall, TPS proton ranges differed from direct measurements by less than 2.2mm. Tab.2 summarises the results of the density uncertainty evaluation. The density uncertainty value associated with the use of Mono+75keV, SECT and DirectSPR images was respectively 2%, 3.5% and 2.8%.