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
Sterotactic radiotherapy uses all except: 
Select and explain. 
A. Linear accelerator, B. Proton beam, C. Gamma knife, D. Electron beam
D: Electron beam
Answer: D: Electron beam 
Explanation: Electron beam is not used in Stereotactic radiosurgery.