Chao Cai1, Guohua Zeng2. 1. Department of Urology, Minimally Invasive Surgery Center, The First Affiliated Hospital of Guangzhou Medical University and Guangdong Key Laboratory of Urology, Guangzhou, China. 2. Department of Urology, Minimally Invasive Surgery Center, The First Affiliated Hospital of Guangzhou Medical University and Guangdong Key Laboratory of Urology, Guangzhou, China. Electronic address: gzgyzgh@vip.sina.com.