Received: 20 November 2019
Accepted: 23 January 2020
First Online: 31 January 2020
Ethics approval and consent to participate
: The need for ethics approval and consent was waived by the Institutional Review Board of the RWTH Aachen University due to the retrospective nature of the study (EK 312/19).
: Not applicable.
: The authors declare that they have no competing interests.