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': 'Which of the following drugs requires a dose adjustment in patient during radiotherapy in order to prevent radiation toxicity ? \nSelect and explain. \nA. Vincristine, B. Dactinomycin, C. Cyclophosphamide, D. 6-Mercaptopurine', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]