1. Technical Chemistry I and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, 45141 Essen, Germany
2. West German Cancer Centre (WTZ), University Hospital Essen, 45147 Essen, Germany
3. Department of Physics, TU Dortmund University, 44227 Dortmund, Germany
4. West German Proton Therapy Centre Essen (WPE), 45147 Essen, Germany
5. German Cancer Consortium (DKTK), 69120 Heidelberg, Germany
6. Department of Particle Therapy, University Hospital Essen, 45147 Essen, Germany
7. Faculty of Medicine, University Hospital Essen, 45147 Essen, Germany