S2086
Physics - Image acquisition and processing
ESTRO 2026
1 Centre of Radiotherapy, National Institute of Oncology, Budapest, Hungary. 2 Institute of Nuclear Techniques, Budapest University of Technology and Economics, Budapest, Hungary. 3 Department of Radiotherapy, Semmelweis University, Budapest, Hungary Purpose/Objective: The accurate mapping of mass density and material composition from CT images in radiation therapy treatment planning is critical for dose calculation with deterministic algorithms such as Varian Acuros XB. The purpose of this study was to investigate the differences between two kernels provided by Siemens Healthineers: a standard CT reconstruction kernel (Qr40) and the Direct Density mass-density reconstruction kernel (Sm40) in terms of the mass- density conversion and the resulting material map. Material/Methods: Single chest-abdomen-pelvis CT scan was acquired using a Siemens SOMATOM go.Sim scanner. The selected patient earlier underwent a lumbo-sacral spinal stabilization surgery with titanium implantation. Two image sets were reconstructed: Qr40 a standard convolution kernel with conventional Hounsfield-unit (HU) to mass density conversion and Sd40 Direct Density reconstruction kernel, which yields voxel values proportional to mass density independent of tube voltage. Derived material-assignment maps were generated based on the built-in physical material table for each reconstruction. Quantitative voxel-based comparison was performed between the two mass- density maps and the two material distributions. Results: The mass-density values provided by Direct Density reconstruction were lightly lower compared the values derived from the standard kernel, the differences appeared at the bone-soft tissue interfaces, as Figure1 shows.
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Conclusion: In this small exploratory study for patients with HNC, FDG was able to conservatively localize HVs as defined by FAZA, and FDG volumes were generally larger than FAZA HVs. Treatment plans with dose escalation to the FDG Clinical volume covered the FAZA HV. This study demonstrates that the spatial correlation of FDG PET and hypoxia PET warrants further investigation. References: 1. Nordsmark M, Overgaard J. Radiotherapy and oncology. 2000;57(1):39–43. 2. Welz S, Mönnich D, Pfannenberg C, et al. Radiotherapy and oncology. 2017;124(3):526–32. 3. Thorwarth D, Eschmann SM, Holzner F, et al. Radiotherapy and oncology. 2006;80(2):151–6. 4. Zegers CML, Hoebers FJP, van Elmpt W, et al. Eur J Nucl Med Mol Imaging. 2016;43(12):2139–46. Keywords: head and neck, hypoxia, PET Digital Poster 4090 Evaluation of Direct Density kernel conversion for mass-density mapping Tamás Pócza 1 , Ákos Sudár 1,2 , Csilla Pesznyák 1,2 , Tibor Major 1,3
Figure1.: Difference between mass density values calculated by Sm40 and and Qr40 kernelsThe ratio of the different materials was changed also depending on which to the material-assignment table was used. The ratios for different reconstructions are shown in Figure2.
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