As the number of patients opting for Gamma Knife treatment increases, some patients continue to experience tumor growth after irradiation. In some patients, the tumor enlargement is small and temporary, most likely related to the irradiation effect of the tumor and its replacement by granulation tissue. Some patients will have a small enlargement of tumor size and then no further change later. These patients do not require further treatment, but need to be monitored continuously. For other patients with persistent tumor growth, a second gamma knife treatment may be required. However, this treatment is still being validated and there is little experience regarding long-term outcomes.