Received: 13 January 2021
Accepted: 14 July 2021
First Online: 20 July 2021
: Conduct of the study was approved by the Institutional Review Board of The University of Tokyo, which waived the requirement for informed consent owing to the anonymity of the data. This study was performed in accordance with the Declaration of Helsinki.
: Not applicable.
: The authors declare that they have no competing interests.