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: B i.e. Iodine -131