Quang Van Le1,2, Duy Quoc Ngo3, Duong The Le1, Quy Xuan Ngo1. 1. Department of Head and Neck Surgery, Vietnam National Cancer Hospital, 30 Cau Buou Street, Thanh Tri District, Hanoi, Vietnam. 2. Hanoi Medical University, 01 Ton That Tung Street, Dong Da District, Hanoi, Vietnam. 3. Department of Head and Neck Surgery, Vietnam National Cancer Hospital, 30 Cau Buou Street, Thanh Tri District, Hanoi, Vietnam. duyyhn@gmail.com.