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
[{'content': 'Best investigation of planning radiotherapy for carcinoma of esophagus? \nSelect and explain. \nA. PET, B. CT Scan, C. USG, D. MRI', 'role': 'user'}, {'content': "Answer: A \nExplanation: 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.", 'role': 'assistant'}]