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
All of the following are used in Interstitial brachytherapy except: 
Select and explain. 
A. CO6deg, B. 4192, C. Au198, D. C5137
A: CO6deg
Answer: A: CO6deg 
Explanation: Ans. CO6deg