S2377
Physics - Quality assurance and auditing
ESTRO 2026
model was iteratively developed to better reproduce the measured dose distributions. This new model featured a lower foam core RED of 0.01 and a higher carbon fiber RED of 1.2. Results: Measured profiles are shown in figure 2. It can be seen that for more posterior angles, the difference between both models is important.
Digital Poster 3236 Modelling of Elekta iBeam EVO couchtop using spatial dose distributions Pablo López Expósito, Andrea Rodríguez Álvarez, Breixo Carmelo Portas Ferradás, Daniel Diaz Martón, Artur Sampayo Muñoz Radiofísica y Protección Radiológica, Hospital Universitario Nuestra Señora De Candelaria, Santa Cruz de Tenerife, Spain Purpose/Objective: The accurate couch modelling within a TPS is crucial, because its impact is, as highlighted by [1] "a complex combination of increased skin dose, reduced tumor dose, and altered dose distribution." Given the rising use of VMAT, where the dose delivered through the couch may be significant, proper characterization of this component is increasingly essential.Elekta currently provides a two-structure couch model in Monaco TPS: a carbon fiber structure with relative electron density, RED = 0.2 and a foam core structure with RED = 0.04. The scheme of the table in Monaco library (and a PMMA phantom) can be seen in Figure 1. The primary purpose of this study is to validate whether this existing model can accurately reproduce the dose distributions for a set of posterior beams using 3D measurements. If the current model proves insufficient, we aim to propose a new model that better fits the measured dose distribution.
Conclusion: It was observed that a better modelling of iBeam EVO couch is possible. The original model in the TPS library predicts higher doses than measured. A better modelling of the tip of the couch is also achievable. While additional fine-tuning of the couch model is feasible, there is a risk that over-fitting could introduce errors in treatment delivery due to inaccuracies in the measurement setup or different patient position relative to the couch during treatment. References: [1] Olch AJ, Antone JD, Bezak E, Chen J, Kim K, Khan AJ, et al. Dosimetric effects caused by couch tops and immobilization devices: Report of AAPM Task Group 176. Med Phys 2014;41(6):061501. Keywords: Modelling, couch top, beam attenuation QA-based validation of synthetic CT (sCT) for clinical implementation in an MRI-only online adaptive MR-guided radiotherapy (oAMRgRT) workflow Simone Raggio 1 , Luca Vellini 2 , Davide Cusumano 2 , Luisa Altabella 3 , Luca Boldrini 1,4 , Giuditta Chiloiro 1 , Randa El Gawhary 5 , Marco Fusella 6 , Matteo Galetto 1 , Gianluca Gragnaniello 1 , Ina Isufi 1 , Matteo Nardini 1 , Giulia Panza 1 , Konstantinos Zormpas-Petridis 7,8 , Angela Romano 1 , Luca Russo 1 , Elena Huong Tran 1 , Claudio Votta 1 , Evis Sala 1,4 , Maria Antonietta Gambacorta 1,4 , Marco De Spirito 1,8 , Lorenzo Placidi 1 1 Diagnostic Imaging and Oncological Radiotherapy, Fondazione Policlinico Universitario A. Gemelli, IRCCS, Rome, Italy. 2 Medical Physics Unit, Mater Olbia Digital Poster Highlight 3257 Hospital, Olbia, Italy. 3 Medical Physics Unit, Azienda Ospedaliera Universitaria Integrata, Verona, Italy. 4 Radiological and Hematological Sciences, Catholic University of the Sacred Heart, Rome, Italy. 5 Radiation Oncology, San Pietro Fatebenefratelli Hospital, Rome, Italy. 6 Department of Radiation Oncology, Abano Terme Hospital, Abano Terme, Italy. 7 Computational
Material/Methods: A set of eight 6 and 10 MV 10x10 cm ² fields were measured on an Elekta Versa HD LINAC. Two fields, set at gantry angles of 45º and -45º, were used for absolute dose correction to account for daily output variations, and air mass corrections. The remaining six beams (at 160º, -160º,140º,-140,120º and -120º) were specifically aimed at assessing couch attenuation.All beams were measured using Delta4 phantom (ScandiDos), a 22 cm cylindrical PMMA phantom, equipped with two orthogonal 2D silicon p-diode arrays.The measured data was initially compared against the dose distributions calculated in Monaco TPS, with XVMC algorithm, 0.2 mm grid size and 0.5% dose uncertainty in the cylindrical phantom of Delta4.Following this initial comparison, a new couch
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