Document is current

Article History

Received: 27 October 2017

Accepted: 7 August 2018

First Online: 13 August 2018

Ethics approval and consent to participate

: This study has been granted an exemption from Dankook university ethics approval because of the retrospective nature of the study and the analysis used anonymous clinical data. A written informed consent was waived by the ethics committee for chart review. The parental consent was not obtained for participants under 16.

: 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.