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 is used for permanent interstitial implant brachytherapy – 
Select and explain. 
A. Boron, B. Cesium – 131, C. Phosphorus, D. Iridium
B: Cesium – 131
Answer: B: Cesium – 131 
Explanation: Permanent implants of interstitial brachytherapy :- Cesium -131, Yttrium, Gold - 198 (Au - 198), 125I, Radon - 222 (Rn - 222), Pallidum -103 (Pd -103).
Temporary implants of Interstitial brachytherapy :- Iridium -  192 (Ir - 192), Cesium - 137 (Cs - 137), Cobalt - 60 (Co - 60),

           Californium, Radium - 226 (Ra - 226), Tantolum.