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Article History

Received: 5 December 2017

Revised: 23 February 2018

Accepted: 16 March 2018

First Online: 30 April 2018

Compliance with ethical standards

:

: The scientific guarantor of this publication is Jin You Kim.

: The authors of this manuscript declare no relationships with any companies whose products or services may be related to the subject matter of the article.

: No complex statistical methods were necessary for this paper.

: Written informed consent was waived by the Institutional Review Board.

: Institutional Review Board approval was obtained.

: • retrospective• observational• performed at one institution