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Article History

Received: 9 August 2018

Accepted: 15 October 2018

First Online: 3 November 2018

Ethics approval and consent to participate

: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional research committee (Asan Medical Center) and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Our institutional review board (Asan Medical Center) approved this retrospective study, and the requirement for informed consent was waived.

: Our institutional review board approved this retrospective study, and the requirement for informed consent and publication was waived.

: The authors declare that they have no competing interests.

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