ESTRO 2025 - Abstract Book

S3651

Physics - Quality assurance and auditing

ESTRO 2025

Conclusion: DirectDensity TM (RED

HU ) overall performs well for lung, fat, soft tissues and bones over the entire range (70-140 kV). Further evaluation is required for dense bone at 70 kV to assess the clinical impact of the higher deviations for some scanners. A scanner model dependency seems apparent for DirectDensity TM . Inter-centre variations in DirectDensity TM HLUT generation were minimal, showing variations only for CT numbers higher than for most human tissues. Future reported scanner-type-specific HLUTs seem possible.

Keywords: DirectDensity algorithm, multicenter study

References: [1] Van der Heyden B, Öllers M, Ritter A, et al. Clinical evaluation of a novel CT image reconstruction algorithm for direct dose calculations. Phys Imaging Radiat Oncol 2017;2:11-16. http://dx.doi.org/10.1016/j.phro.2017.03.001. [2] Peters N, Taasti VT, Ackermann B, et al. Consensus guide on CT-based prediction of stopping-power ratio using a Hounsfield look-up table for proton therapy. Radiother Oncol 2023;184:109675. https://doi.org/10.1016/j.radonc.2023.109675. We thank all participating centres for facilitating the site visits, for their time and effort and for sharing the data. We thank Kenneth Ruchala (Sun Nuclear Corporation) for kindly providing the phantom.

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Digital Poster Different methods of quality assurance for dose accumulation in the reirradiation scenario Luisa Sabrina Stark 1 , Nicolaus Andratschke 1 , Madalyne Day 1 , Matthias Guckenberger 1 , Izabela Pytko 1 , Jonas Willmann 1,2 , Stephanie Tanadini-Lang 1 1 Radiation Oncology, University Hospital Zürich, Zürich, Switzerland. 2 Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, USA

Purpose/Objective: Due to the lack of ground truth in image registration, a safe handling of uncertainties is crucial. The risk of toxicity