Can pet scan always diagnose /confirm presence of lung cancer or can only give indication and later biopsy is vital to confirm cancer if a nodule seen?

Bx definitive. A positron emission tomography (pet) scan is an imaging test that uses a radioactive substance called a tracer to look for disease in the body. It is often used to determine the treatment of cancer, if it is spreading, or improving, etc. Used in combination with tests such as ct or mri, it can provide a very high index of suspicion for cancer, but a bx is always definitive and used for tx.