A Pilot Trial of Adjuvant Hypofractionated Stereotactic Radiosurgery for Intermediate-risk Meningioma (SRS-AIM)

Inclusion Criteria: * Age \>+ 18 years at time of study entry * Ability to understand and the willingness to sign a written informed consent document. * Histologic diagnosis of newly diagnosed World Health Organization (WHO) grade 2 or recurrent WHO grade 1 meningioma. With regard to recurrent WHO grade 1 meningioma, participants must present with radiographic evidence of recurrence, and have a histologic diagnosis of WHO grade 1 meningioma at the most recent resection. \* Note: For participants diagnosed outside of University of California San Francisco (UCSF), re-review of pathology at UCSF is strongly encouraged. Hematoxylin and eosin (H\&E) slides will be reviewed by UCSF pathologists. * Participants must have undergone a gross-total surgical resection as deemed by their neurosurgeon (Simpson grade I-III resection), using all available information which can include post-operative MRI, of a meningioma within 180 days of enrollment. * Participants must have a pre-operative MRI. * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 (Karnofsky score of 70 or higher) * Participants must have post-operative MRI indicating anatomy suitable for hypofractionated radiosurgery, as reviewed by the Radiation Oncology co-principal investigators (PIs). Exclusion Criteria: * Concurrent participation in another clinical study with an investigational product unless it is an observational (non-interventional) study or the follow-up period of an interventional study. * Extensive multifocal (3 or more meningiomas) or metastatic disease. * Participants with tumors within 2mm of the optic apparatus or brainstem will be excluded. * Participants with another active primary malignancy or history of previous malignancy (except non-melanoma skin cancers, low and favourable-intermediate risk prostate cancers, and in situ cancers such as bladder, gastric, colon, cervical/dysplasia, or breast) are excluded unless a complete remission was achieved at least 2 years prior to study entry and no additional therapy is required or anticipated to be required during the study period. * Female participants who are pregnant. * Any underlying medical or psychiatric condition that, in the opinion of the investigator, would interfere with evaluation of study treatment or interpretation of participant safety or study results. * Participants with uncontrolled seizures, defined as greater than 3 disabling seizures per day while on anti-epileptic drugs. * Participants who have had previous intracranial radiotherapy overlapping with the area that would be targeted for stereotactic radiosurgery by this study.