Received: 23 April 2018
Accepted: 12 September 2018
First Online: 21 September 2018
Ethics approval and consent to participate
: This study was approved by the Institutional Review Board of Yonsei University Hospital (No. 4–2018-0110). The need for patient consent was waived by the Review Board as the study involved minimal risk and its retrospective nature meant that no identifiable information was used.
: Not applicable.
: The authors declare that they have no competing interests.
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