Received: 25 May 2020
Accepted: 22 December 2020
First Online: 6 January 2021
Ethics approval and consent to participate
: This project was approved by the Institutional Review Board of the Korea University (IRB: KUIRB-2019-349-1). Informed consent was waived because the data were de-identified before the analysis.
: Not applicable.
: The author(s) declare no conflicts of interest.