Received: 12 September 2019
Accepted: 31 March 2020
First Online: 15 April 2020
Ethics approval and consent to participate
: The protocol for this study was reviewed and approved by our Institutional Review Board of Tokyo Medical University Ibaraki Medical Center (No.14–5). This was a retrospective study. The IRB waived the requirement to obtain a signed consent form.
: Not applicable.
: None of the authors has any conflict of interest to disclose.