Received: 2 August 2018
Accepted: 5 December 2018
First Online: 6 January 2019
Ethics approval and consent to participate
: The study protocol was approved by the ethics committee of the Sapporo Medical University, Hokkaido, Japan. In addition, the clinical trial study protocol was also checked and approved by the institutional review board of Sapporo Medical University, Hokkaido, Japan.
: Since this was a retrospective study, patient consent was not considered necessary; however, all relevant research information was disclosed.
: The authors declare that they have no competing interests.
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