Radiotherapy is one of the main treatment methods for patients with lung cancer, especially for patients with locally advanced lung cancer. Local advanced lung cancer is often accompanied by atelectasis, so it brings great difficulty and uncertainty to the delineation of radiotherapy target, and then affects the curative effect of patients. The latest research shows that functional imaging has a unique imaging principle, which can truly reflect biological information such as tumor proliferation and metabolism, and has an application prospect in distinguishing the target area of lung cancer from atelectasis.