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
[{'content': 'Which of the following isotope is commonly used in teletherapy: September 2010 \nSelect and explain. \nA. Cesium, B. Iridium, C. Technetium, D. Iodine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. A: Cesium Cobalt-60 and Cesium-137 sources are the most common ones used in radiotherapy.', 'role': 'assistant'}]