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': 'Commonly used type of radiation in radiotherapy is: \nSelect and explain. \nA. Alpha rays, B. Beta rays, C. Gamma rays, D. X-rays', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. Gamma rays', 'role': 'assistant'}]