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': 'Latest source of neutrons for radiotherapy is: \nSelect and explain. \nA. Strontium-90, B. Iodine-131, C. Calcifornium-256, D. Radium-226', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. Calcifornium-256', 'role': 'assistant'}]