When edema occurs after radiotherapy for brain metastasis of lung cancer, the main treatment is to reduce the intracranial pressure by using mannitol for dehydration, which is a very good way. After lung cancer patients develop brain metastasis, they are prone to brain edema, which can increase intracranial pressure and cause headache, dizziness, nausea and vomiting. At this time, patients should be given mannitol immediately to lower the cranial pressure first, so as to relieve the symptoms and the formation of brain herniation. In addition, the use of hormones can have the effect of reducing cerebral edema and relieving intracranial pressure. Depending on the severity of cerebral edema, it can be given once a day or once every 12 hours, once every 8 hours, and even when the cerebral edema is severe, some patients need to lower the cranial pressure once every 6 hours. If the treatment has been finished, the tumor cannot shrink and the cranial pressure cannot be lowered, i.e. there is a lesion present, but the amount of radiotherapy has been enough, the patient is dependent on mannitol, there will be cerebral edema once it is stopped, and the cerebral edema will be reduced once it is used, it is necessary to ask neurosurgery to help remove the lesion and completely solve the problem of high cranial pressure.