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': 'All may be used in interstitial brachytherapy except \nSelect and explain. \nA. Cs137, B. Au192, C. Ir192, D. Co60', 'role': 'user'}, {'content': 'Answer: D \nExplanation: D i.e. C060', 'role': 'assistant'}]