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
Out of the following which is not a radiotherapy equipment? 
Select and explain. 
A. Betatron, B. Telecurie-cobalt unit, C. Linear accelerator, D. Thimble chamber
D: Thimble chamber
Answer: D: Thimble chamber 
Explanation: Ans. Thimble chamber