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
Radioisotope used for thyroid treatment of metastasis/ ablation: 
Select and explain. 
A. I-123, B. I-131, C. I-83, D. I-90
B: I-131
Answer: B: I-131 
Explanation: Ans. B. I-131* 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.* I-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.