1 Department of Radiation Oncology, RWTH Aachen University, Aachen, Germany.
2 Department of Radiation Oncology, RWTH Aachen University, Aachen, Germany; Department of Radiation Oncology, MediClin Robert Janker Klinik, Bonn, Germany.
3 Department of Radiation Oncology, RWTH Aachen University, Aachen, Germany; Department of Radiation Oncology, MediClin Robert Janker Klinik, Bonn, Germany. Electronic address: michael.pinkawa@post.rwth-aachen.de.