Observation or Radiation Therapy in Treating Patients With Newly Diagnosed Grade II Meningioma That Has Been Completely Removed by Surgery

Inclusion Criteria: * PRIOR TO STEP 1 REGISTRATION: * The patient must have a newly diagnosed unifocal intracranial meningioma, gross totally resected, and histologically confirmed as WHO grade II based upon pathology findings at the enrolling institution. WHO grade will be assigned according to WHO 2016 criteria * Gross total resection (GTR) will be interpreted as modified Simpson grade 1-3 without gross residual dural-based or extradural tumor. GTR must be confirmed both by modified Simpson grade and by post-operative magnetic resonance imaging (MRI) findings. The modified Simpson grade can be inferred from the operative report (surgeon does not need to explicitly describe the Simpson grade for the purposes of eligibility) * Step 1 registration must occur within 180 days of the initial surgery; this will provide sufficient time for post-operative imaging confirmation of resection extent after resolution of operative changes. Moreover, it will permit additional surgery if needed to achieve a GTR. Within this 180 day interval, a second surgery is permitted in order to achieve GTR, but even with a second surgery, Step 1 registration must occur within 180 days of the initial resection * GTR must be confirmed on post-operative imaging following the most recent surgery. For protocol enrollment, the assessment of GTR will be made at each site. However, submission of both pre-operative and post-operative MRIs is required for patients. If a second surgery is performed, submission o…