This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Radiotherapy, Subject name: Radiology
[{'content': 'Radioisotope used for thyroid treatment of metastasis / ablation \nSelect and explain. \nA. 1-123, B. 1-131, C. Jan-83, D. Jan-90', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. (b) 1-131Ref: Sutton 7th/1504* Iodine-131 has a radioactive decay half-life of about eight days.* Iodine-131 exhibits a beta mode of decay, and leads to death in cells that it penetrates up to several millimeters and hence is useful for thyroid ablation.* 1-123 has a half-life of 13.22 hours and is a radioactive isotope of iodine used in nuclear medicine imaging, including single photon emission computed tomography.', 'role': 'assistant'}]