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
Brachytherapy is the internal radiation therapy procedure for treating tumors. All are used in brachytherapy, EXCEPT: 
Select and explain. 
A. I 125, B. I 131, C. Cs 137, D. Iridium 192
B: I 131
Answer: B: I 131 
Explanation: Clinically used isotopes in brachytherapy include iridium 192 (192 Ir), iodine 125 (125 I), cobalt 60 (60 Co), cesium 137 (137 Cs), gold 198 (198 Au), and palladium 103 (103 Pd). Iodine 131 is not used in brachytherapy. Ref: Nuclear Development Beneficial Uses and Production of Isotopes 2004 Update ... By OECD, Nuclear Energy Agency, 2005, Page 23; Brachytherapy: Applications and Techniques By Phillip M. Devlin, M.D., 2007, Page 52.