ESTRO 2025 - Abstract Book

S3695

Physics - Quality assurance and auditing

ESTRO 2025

Conclusion: Implementing a 40% mAs reduction in pelvic CBCT protocols effectively decreases patient dose without compromising image quality or registration usability. While increased noise affects CBCT HU values and dose recalculation accuracy, the impact on sCT generation is minimal. These findings support the feasibility of dose optimization in prostate image-guided radiotherapy without sacrificing clinical efficacy.

Keywords: IGRT, optimisation, prostate

References: [1] Alaei, Parham et al. Imaging dose from cone beam computed tomography in radiation therapy. Physica Medica: European Journal of Medical Physics.

[2] Wood TJ, Moore CS, Horsfield CJ, Saunderson JR, Beavis AW. Accounting for patient size in the optimization of dose and image quality of pelvis cone beam CT protocols on the Varian OBI system. Br J Radiol.

[3] Agnew CE, McCallum C, Johnston G, Workman A, and Irvine DM. (2021) Optimisation of Varian TrueBeam head, thorax and pelvis CBCT based on patient size. Journal of Radiotherapy in Practice.

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Digital Poster Clinical Validation of a commercial Monte Carlo based platform for patient-specific quality assurance in proton therapy Giuseppe Castiglione Minischetti 1 , Davide Alio 1 , Federica Cattani 1 , Stefania Comi 1 , Marco Liotta 1 , Floriana Pansini 1 , Daniela Alterio 2 , Barbara Alicja Jereczek 2 1 Medical Physics Unit, European Institute of Oncology, MIlan, Italy. 2 Radiotherapy Department, European Institute of Oncology, Milan, Italy Purpose/Objective: This study aims to clinically validate a commercial independent dose calculation software ( myQA iON , IBA-Dosimetry) for PSQA in proton therapy. Material/Methods: The first part of this study involved box-shaped dose distribution planned on our TPS (RayStation version 12A SP1) using both a water phantom and a homemade heterogeneous phantom simulating a tissue-lung interface. These plans were recalculated in myQA iON. 2D transversal dose distributions and distal R 90 (range at 90% dose in the distal falloff) values were extracted from computed data (TPS and myQA iON) and measured using MatriXX and Zebra detectors, respectively (IBA-Dosimetry). Dose distributions from TPS and myQA iON were compared using the 3D Gamma Passing Rate (GPR) with a global gamma index ( 2%/2mm criteria). In the second part of this study, 25 clinical plans for various anatomical sites (breast, H&N, pelvis, brain, thorax) were analyzed. Beams from these plans were recalculated in myQA iON twice, with and without accounting for irradiation log-files. The resulting beam dose distributions were compared with the planned ones using a 3D GPR (global gamma index, 2%2mm ). Results: In the water phantom analysis, distal R 90 values from TPS and myQA iON computations differed from measured values by 0.5±0.4mm and 0.9±0.7mm , respectively. Dose profiles also showed good agreement, with differences in Full Width