Received: 10 June 2020
Accepted: 31 January 2021
First Online: 12 February 2021
Ethics approval and consent to participate
: 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.This study was approved by Peking university third hospital ethics committee. “For this type of study (retrospective study), formal consent is not required”.No additional administrative permissions were needed.
: Not applicable.
: Ang Gao, Yongqiang Wang, Miao Yu, Xiaoguang Liu declare that they have no conflict of interest.