Received: 11 July 2019
Accepted: 28 February 2020
First Online: 12 March 2020
Ethics approval and consent to participate
: The protocol received Institutional Review Board approval of the Yonsei University College of Medicine and was performed in accordance with the ethical standards described in the Declaration of Helsinki. The requirement to obtain a written informed consent was waived by the Institutional Review Board of the Yonsei University College of Medicine because our study was retrospective research based on medical records, and this research presented no more than minimal risk of harm to subjects.
: The authors declare that they have no competing interests.