Received: 5 May 2018
Accepted: 1 October 2018
First Online: 15 October 2018
Ethics approval and consent to participate
: This retrospective study was approved by the Institutional Review Board of Asahikawa Medical University with reference number AMU 800, and informed consent was waived by the IRB due to the retrospective nature of the study.
: Not applicable.
: The authors declare that they have no competing interests.
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