1 Department of Pediatrics and Pediatric Hematology/Oncology, University Children's Hospital, Carl von Ossietzky University of Oldenburg, Klinikum Oldenburg AöR, 26133, Oldenburg, Germany.
2 Division of Epidemiology and Biometry, Carl von Ossietzky University of Oldenburg, 26129, Oldenburg, Germany.
3 Department of Pediatrics and Pediatric Hematology/Oncology, University Children's Hospital, Carl von Ossietzky University of Oldenburg, Klinikum Oldenburg AöR, 26133, Oldenburg, Germany. mueller.hermann@klinikum-oldenburg.de.