1Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany, 2Department of Radiology, German Cancer Research Center, Heidelberg, Germany, 3Department of Diagnostic and Interventional Radiology, University Medical Center Ulm, Ulm, Germany, 4Medical and Biological Informatics, German Cancer Research Center, Heidelberg, Germany, 5Institue of Physics, Johannes Gutenberg University Mainz, Mainz, Germany