I often have patients ask me, “Dr. Sai, what is the gamma knife?” In fact, the gamma knife is not really a “scalpel”, it actually belongs to the stereotactic radiotherapy system, is a kind of radiation therapy. Gamma knife is the use of modern imaging means to locate intracranial lesions, and then high-energy rays focused on the lesion, the lesion will be destroyed, similar to the use of a magnifying glass to focus the sunlight, can be ignited as a match head. Because of the focused energy of the gamma knife, less damage to the surrounding tissue, similar to the “knife cut”, hence the name. Gamma knife is widely used in neurosurgery, mostly for the volume of less than 3cm, deep in the location (such as the brainstem and skull base), the risk of surgery is large lesions. It is also used for the treatment of certain recurrent tumors (gliomas, meningiomas and pituitary tumors, etc.). Because of the relatively low risk and short treatment time without surgery, some doctors often refer patients for gamma knife treatment, and patients are often happy to accept it. However, gamma knife also has its disadvantages. First, some tumors, especially malignant tumors, cannot be eradicated by surgery or radiotherapy alone, and chemotherapy must be administered after clear pathology (e.g., intracranial germ cell tumors and primary central nervous system lymphomas). Gamma knife cannot cut lesions to clarify the pathology, and therefore cannot guide the next step of treatment, making it possible for some lesions to recur in the short term, making follow-up treatment more difficult. In addition, after gamma knife treatment, lesions will produce necrosis, and if necrosis occurs within a short period of time, it will lead to larger lesion size, which will aggravate the patient’s original symptoms, and in some cases, the occupancy effect will be more obvious, and further surgical resection will be necessary. Therefore, gamma knife treatment for brain tumor must be cautious and must be based on the possible nature, location and size of the lesion and the patient’s general condition, and should not be used lightly.