This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
Patient with carcinoma endometrium treated with pelvic external beam irradiation to whole pelvis. Which of the following organs is most radiosensitive in the pelvic region? 
Select and explain. 
A. Ovary, B. Vagina, C. Bladder, D. Rectum
A: Ovary
Answer: A: Ovary 
Explanation: Ans: A. Ovary(Ref Perez and Brady's Principles of Radiation Oncology 6/e p65)Among the given options, most radiosensitive organ is ovary >rectum >bladder >vagina.(Radiation tolerance dose: Ovary = 2-3 Gy; Rectum = 60 Gy; Bladder = 65 Gy; Vagina = 90 Gy).