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
Best investigation of planning radiotherapy for carcinoma of esophagus? 
Select and explain. 
A. PET, B. CT Scan, C. USG, D. MRI
A: PET
Answer: A: PET 
Explanation: Ans. is'a'i.e., PETPrior to radiotherapy, the extent of tumor and its spread is assessed to target t}re area for radiotherapy.CT scan, endoscopic USG and FDG-PET are used for esophageal carcinoma, bt for accurate radiotherapy planning PET scan is far superior to CT or endoscopic USG.