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': 'Stereotactic radiosurgery uses all except – \nSelect and explain. \nA. Proton, B. Electron, C. Linear accelerator, D. Gamma knife', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Stereotactic radiosurgery uses :- (i) Ca - 60 (Gamma knife); (it) X-ray knife (Linear accelerator); (iii) Cyclotron (Proton beam).', 'role': 'assistant'}]