Received: 7 October 2018
Accepted: 31 January 2019
First Online: 8 February 2019
Ethics approval and consent to participate
: This retrospective study was approved by the Institutional Review Board of Kangbuk Samsung Hospital (No. 2016–10–030-004). The waiver of individual patient informed consent was obtained due to minimal risk nature of this study.
: Not applicable.
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.