Received: 1 September 2019
Accepted: 3 March 2020
First Online: 11 March 2020
Ethics approval and consent to participate
: This study was approved by the Faculty of Medicine Research Ethics Committee, Kyorin University (approval No. H30–196). The review board waived the requirement for consent due to the retrospective nature of the study.
: Not applicable.
: The authors declare that they have no competing interests.