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': 'Gamma knife – a) Steel knifeb) Used for cutting tumours in difficult locationc) Cobalt is usedd) Recovery delayed \nSelect and explain. \nA. a, B. c, C. ac, D. bc', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Gamma knife is used for stereotactic radiosurgery for tumors in difficult locations e.g. deep seated brain tumors. It contains Cobalt - 60 sources.', 'role': 'assistant'}]