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': 'What is the principle behind radiotherapy in malignancy? \nSelect and explain. \nA. Ionisation of DNA, B. Dehydration of DNA, C. Charring the nucleus, D. Ultrasonic effect', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Radiotherapy is the treatment of cancer with ionizing radiation. It works by damaging the DNA within the tumor cells, making them unable to divide and grow. The goal of radiation therapy is to maximize the dose to tumor cells while minimizing exposure to normal, healthy cells. Ref: Emami B et al. 1991', 'role': 'assistant'}]