[1] Department of Physics, SUPA and University of Strathclyde, Glasgow, United Kingdom
[2] Physikalisch-Technische Bundesanstalt (PTB), Dosimetry for Radiation Therapy and Diagnostic Radiology, Braunschweig, Germany
[3] National Physical Laboratory, Medical Radiation Science, Teddington, United Kingdom
[4] Physikalisch-Technische Werkstätten (PTW), Freiburg,RD, Germany
[5] University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University Oldenburg, Oldenburg, Germany