Hi! I understand your fear. PET scans are extremely sensitive. Infection or scarring from something previous can show up on scan in the lungs. I've seen it happen as I work for a dermatoligist. So this may or may not be related to his melanoma. Know that your dad has done everything he is supposed to do to beat this so I would say it is now in God's hands. I hope the best result for him. Pray as I will.