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': 'In radiation therapy, it is desirable to use linear accelerators in treating cancers. Which rays are produced by linear accelerators? \nSelect and explain. \nA. X rays, B. Beta rays, C. Gamma rays, D. Neutrons', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A linear accelerator or "linac" produces high-energy x-rays. The linear accelerator is a device that uses high-frequency electromagnetic waves to accelerate charged paicles such as electrons to high energies through a linear tube. The high-energy electron beam itself can be used for treating superficial tumors, or it can be made to strike a target to produce x-rays for treating deep seated tumors. Ref: The Physics of Radiation Therapy By Faiz M. Khan, 2012, Page 38; Oxford oncology 2nd edition, Page 398', 'role': 'assistant'}]