Received: 21 September 2017
Accepted: 8 March 2018
First Online: 13 March 2018
Ethics approval and consent to participate
: This retrospective study was approved with the ethical board of Shimane University Faculty of Medicine, and was conducted in accordance with the Declaration of Helsinki. Informed consent was obtained from all individual participants included in the study.
: Not applicable.
: The authors declare that they have no competing interests.
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