Daniel A. Pryma, MD of the University of Pennsylvania highlights one common question – when should a patient have his first PET Scan for lung cancer. He explains that if you scan an image of nodules less than 8mm, its very unlikely to have a PET CT result that can change what you can do for the patient. With that, the best thing to do is wait and then do a Chest CT for the patient. Lung cancer occurs in nodules over 8mm.