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
Which of the following isotope is commonly used in teletherapy: September 2010 
Select and explain. 
A. Cesium, B. Iridium, C. Technetium, D. Iodine
A: Cesium
Answer: A: Cesium 
Explanation: Ans. A: Cesium Cobalt-60 and Cesium-137 sources are the most common ones used in radiotherapy.