Lung cancer is advanced once metastasis occurs, both of which are more serious cases. If it must be clear which is the most serious organ, it should be the brain, especially the brain stem. If lung cancer has brain metastasis it will be more difficult to treat because most drugs are difficult to enter brain tissue, caused by the presence of blood-brain barrier in the body. This is when radiotherapy is given, which is only a local treatment. After local control, there is a possibility that new tumors may reappear in other places outside the shooting field, leading to the failure of subsequent treatment. In addition, among brain tissues, metastasis of lung cancer to the brainstem and medulla oblongata is the top priority. Why? Because the brainstem and medulla oblongata are the life centers of the body, and they are also very tricky to treat. Even small lesions may lead to compression of the brainstem and medulla oblongata, resulting in the termination of heartbeat and respiration and death of the patient.