Text and Data Mining valid from 2018-05-31
Received: 8 March 2018
Accepted: 28 May 2018
First Online: 31 May 2018
Compliance with ethical standards
: Ryo Yamamoto, Masaru Suzuki, Rakuhei Nakama, Kenichi Kase, Kazuhiko Sekine, Tomohiro Kurihara, and Junichi Sasaki declare that they have no conflict of interest.
: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
: For this type of retrospective study, formal consent is not required.