The risk factors of biliary fistula after radical resection of perihilar cholangiocarcinoma in elderly patients and its influence on prognosis: a retrospective cohort study - Yin, Rong; Xu, Shasha; Gong, Yin; Zhu, Jing; Zhu, Haiou; Tao, Yan; Li, Xiangcheng (Journal of Gastrointestinal Oncology, 2023)