Conflict of Interest

Joon Ho Choi and Jin-Sook Ryu declare that they have no conflict of interest.

Ethics Approval

All procedures performed in study involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Consent to Participate

The institutional review board of our institute approved this retrospective study, and the requirement to obtain informed consent was waived.

Consent for Publication

The institutional review board at our institution approved this retrospective study, and the requirement to obtain informed consent was waived.