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
Which of the following radioactive isotopes is not used for brachytherapy – 
Select and explain. 
A. Iodine–125, B. Iodine–131, C. Cobalt–60, D. Iridium–192
B: Iodine–131
Answer: B: Iodine–131 
Explanation: None