This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Radiotherapy Pa 1, Subject name: Radiology
All among the following radioisotope are used as permanent implant except: 
Select and explain. 
A. Iodine-125, B. Palladium-103, C. Gold-198, D. Caesium-137
D: Caesium-137
Answer: D: Caesium-137 
Explanation: Caesium-137 is not used as permanent implant for Brachytherapy Permanent implants for brachytherapy Iodine-125 Palladium-103 Gold-198 Caesium-131