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Article History

Received: 18 December 2017

Accepted: 18 July 2018

First Online: 24 July 2018

Ethics approval and consent to participate

: This retrospective study was approved by the ethics committee of the Niigata University School of Medicine (approval number 2442) and was carried out in accordance with the 1975 Helsinki Declaration. Because of the anonymous nature of the data and the opt-out disclosed on our institution’s homepage (ExternalRef removed), the requirement for additional informed consent to participate in this study was deemed unnecessary according to the Japanese national regulation “Ethical Guidelines for Medical and Health Research Involving Human Subjects” (ExternalRef removed).

: Not applicable.

: The authors declare that they have no competing interests.

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