The steps of cranial gamma knife treatment mainly include: installation of the positioning head frame, localization of the lesion, development of the treatment plan, implementation of the treatment plan, and the end of the treatment. (1) Installation of the positioning frame (Figure 1-12): this is the first step of cranial gamma knife treatment. Except for children and psychiatric patients who cannot cooperate with intravenous compound anesthesia, all patients are installed the positioning frame under local anesthesia. The basic principle of installing the frame is to try to make the lesion located in the center of the positioning frame, choose four screws of suitable length, and fix the frame firmly on the patient’s head. This is the only part of the gamma knife treatment where some pain and swelling is felt, and the pain and swelling usually disappears after a few minutes. (2) Lesion localization (Figure 1-13): Generally only one image is needed to localize the lesion, and CT or MRI is chosen according to the location and nature of the lesion, and nowadays MRI is mostly chosen clinically for localization. Install the focal localization CT or MRI frame on the frame (ZunRi Gamma Knife only needs one frame, both are compatible and more convenient), through the CT or MRI adapter, the patient’s head is fixed horizontally on the CT or MRI examination bed, and then the flat scan and enhanced scan (the scanning mode will vary for different disease types), generally 3mm thin layer without interval continuous scan. The scanned image then has the marker points needed to establish 3D coordinates, and the lesion is precisely localized for use in gamma knife treatment planning. (3) Development of the treatment plan (Figure 1-14): This is done by the Gamma Knife dedicated computerized treatment plan design system. Gamma Knife treatment plan design systems produced by different companies vary in interface and function, but the general design steps are basically the same. The physician and physicist design, calculate the treatment target three-dimensional coordinate value, collimator size, gamma angle, each target irradiation time, etc., in order to make the size and shape of the gamma ray focus point with the size and shape of the lesion exactly conformal match. Print out the treatment plan and transmit the treatment plan to the Gamma Knife operation control system. (4) Implementation of the treatment plan (Figure 1-15): At this step, we really enter the substantial treatment phase of the Gamma Knife. The patient enters the treatment room, and the medical technician adjusts the three-dimensional coordinate values X, Y, Z of each target point (Leksell C-type gamma knife and the new gamma knife of Masip can automatically adjust the coordinate values) and the gamma angle in strict accordance with the treatment plan. Turn on the treatment control system start button, the bed will automatically send the patient into the treatment position. Its entire treatment process is automatically controlled by computer, and the doctor observes and monitors the patient’s treatment through the visual intercom system (Figure 1-16), and can immediately terminate the treatment if there is any unexpected situation. The patient is awake during the treatment and does not feel any discomfort. (5) End of treatment: After the treatment is implemented in strict accordance with the treatment plan, the control system automatically withdraws the patient and closes the protective door. The positioning frame is removed, the fixation point is disinfected and wrapped, and the treatment is finished.