Received: 31 March 2020
Accepted: 8 May 2020
First Online: 13 May 2020
Ethics approval and consent to participate
: We have obtained the approval of the institutional review board of the University of Tokyo (IRB (#2203-(6)). At our institution, informed consent was obtained from all surgery patients in advance for the use of data for scientific research and publication.
: Not applicable.
: The authors declare that they have no competing interests.