ESTRO 37 Abstract book

S1149

ESTRO 37

motion is expected, an adaptive treatment strategy is necessary for radiotherapy in children. EP-2088 Quantification of image quality parameters of dual energy CT using software for quality control B. Pawalowski 1,2 , H. Szweda 1 , D. Radomiak 1 , K. Matuszewski 1 , U. Sobocka- Kurdyk 3 , A. Skrobala 1,4 , T. Piotrowski 1,4 1 Greater Poland Cancer Centre, Medical Physics Department, Poznan, Poland 2 Poznan University of Technology, Department of Technical Physics, Poznan, Poland 3 Greater Poland Cancer Centre, Medical Physics Department, Kalisz, Poland 4 Poznan University of Medical Science, Department of Electroradiology, Poznan, Poland Purpose or Objective The first aim of this study was to perform quantification analysis of low contrast resolution and corresponding parameters like signal to noise ratio (SNR) and noise of dual energy CT using CATPHAN phantom and ARTISCAN software. The second aim was to determine the optimal parameters for the best image quality of monoenergetic scans. Material and Methods The ability of dual-energy computed tomography (CT) to differentiate materials with similar CT number but different atomic composition makes this method very interesting for many clinically applications. Dual-energy CT could also improve quality of images like low contrast, signal to noise ratio and noise. To evaluate this image quality parameters two sets of CATPHAN phantom scans using dual-energy mode (80 and 140 keV) were acquired on CT Siemens Definition AS. This phantom has special modules for low contrast, SNR and noise evaluation. Low contrast module has three sets of discs with different contrast (1%, 0.5% and 0.3%). Furthermore each sets has 9 discs with different diameter (2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 15 mm). Then sixteen monoenergetic series were created using dedicated software from Siemens. Scans were created every 10 keV from 40 keV to 190 keV. Next the ARTISCAN software from Aquilab was used for analysis. This software using mathematical formulas provide quantitative information about detected and undetected disc, SNR and noise. For all scans low contrast resolution, signal to noise ratio and noise was computed and compared between each monoenergetic series. Results All monoenergetic series were analyzed using ARTISCAN software. This program provides quantitative and objective analysis of evaluated parameters. For every sets low contrast resolution, signal to noise ratio (SNR) and noise were computed and evaluated. The low contrast resolution is defined as the diameter of the smallest detected object. Therefore the number of detected disc was evaluated. The best low contrast resolution was obtained for 60 keV and 70 keV. Table 1 presents detected and undetected disc and low contrast resolution expressed as diameter of the smallest detected disc. Next evaluated parameter was signal to noise ratio. The highest and therefore the best value was obtained for 60 keV and was 315 a.u. For comparison median value for SNR was 107 a.u. for all energies. Also for the calculated noise the smallest value therefore the best was for 60 keV and was 0,42%. For comparison the biggest value was 2,19% for 40 keV. Table 2 presents results for SNR and noise. Conclusion In this study a significant difference between low contrast resolution, SNR and noise for different energies have been observed. For improve low contrast resolution, signal to noise ratio and noise dual energy CT can be used. The best results for every evaluated parameters

were obtained for 60 keV. In future reconstructed monoenergetic scans for 60 keV will be analyzed for potentially clinical use for delineation tumor. EP-2089 Dual-energy CT enables dose calculation on scans with iodinated contrast agent C. Möhler 1,2,3 , P. Wohlfahrt 4,5 , N.H. Nicolay 2,6,7 , C. Richter 4,5,8,9 , S. Greilich 1, 1 German Cancer Research Center DKFZ, Medical Physics in Radiation Oncology, Heidelberg, Germany 2 National Center for Radiation Research in Oncology NCRO, Heidelberg Institute for Radiation Oncology HIRO, Heidelberg, Germany 3 Heidelberg University, Department of Physics and Astronomy, Heidelberg, Germany 4 OncoRay – National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus- Technische Universität Dresden- Helmholtz-Zentrum Dresden - Rossendorf, Dresden, Germany 5 Helmholtz-Zentrum Dresden - Rossendorf, Institute of Radiooncology - OncoRay, Heidelberg, Germany 6 Heidelberg University Hospital, Department of Radiation Oncology, Heidelberg, Germany 7 German Cancer Research Center DKFZ, Clinical Cooperation Unit for Radiation Oncology, Heidelberg, Germany 8 Department of Radiotherapy and Radiation Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus- Technische Universität Dresden, Dresden, Germany 9 German Cancer Consortium DKTK, partner site Dresden, Dresden, Germany Purpose or Objective Radiotherapy planning commonly requires an additional, ‘native’ CT scan for dose calculation if a contrast agent is used for tumor diagnostics and contouring. Iodinated contrast agents increase CT numbers (Hounsfield units) due to the large atomic number of iodine (Z=53), while electron density remains almost unchanged owing to its low concentration (Figure 1). With dual-energy CT (DECT), the impact of atomic number on CT image contrast can be removed, enabling the direct calculation of relative electron density (RED) for photon therapy and stopping-power ratio (SPR) for ion therapy, respectively. In this study, we are investigating the magnitude of the remaining impact of an iodinated contrast agent on DECT-derived RED/SPR and subsequent clinical treatment planning for both photon and ion therapy.