Funding for this research was provided by:
Japan Society for the Promotion of Science (17K17045)
Ministry of Health, Labour and Welfare (H28-Seisaku-Shitei-009)
Received: 10 October 2018
Accepted: 21 January 2019
First Online: 30 January 2019
Ethics approval and consent to participate
: The institutional review board of the Tokyo Medical and Dental University approved this study (#788). Informed consent from each patient was waived because of the retrospective design of the study and the use of anonymized patient and hospital data.
: Not applicable
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.