Received: 16 August 2018
Accepted: 18 April 2019
First Online: 14 May 2019
Ethics approval and consent to participate
: The study was approved by the Institutional Review Board of Severance Hospital, Yonsei University College of Medicine (approval number: 4–2017-0454). The consent to participate was not required due to the retrospective nature of this study.
: Not applicable.
: The authors declare that they have no competing interests.
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