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': 'Sterotactic radiotherapy uses all except: \nSelect and explain. \nA. Linear accelerator, B. Proton beam, C. Gamma knife, D. Electron beam', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Electron beam is not used in Stereotactic radiosurgery.', 'role': 'assistant'}]