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: Ans. Iodine-131