DISEASE CHARACTERISTICS:

• Histologically proven glioblastoma or gliosarcoma

  • Diagnosis must be made by open biopsy or tumor resection

    • Diagnosis by stereotactic biopsy not allowed
  • Tumor must have supratentorial component

  • Contrast-enhanced MRI or CT scan (if MRI is not available) of the brain must be performed preoperatively and postoperatively prior to initiation of radiotherapy, within 28 days prior to study entry

    • If pre- and postoperative contrast-enhanced CT scans are obtained, must be of sufficient quality

• Meets 1 of the following recursive positioning analysis classifications:

  • Class III

    • Age < 50 years and Karnofsky performance status (KPS) 90-100%

  • Class IV, meeting 1 of the following criteria:

    • Age < 50 years and KPS < 90%
    • Age ≥ 50 years and KPS 70-100% and underwent prior partial or total tumor resection with no worse than minor neurofunction impairment

  • Class V, meeting 1 of the following criteria:

    • Age ≥ 50 years and KPS 70-100% and underwent prior partial or total tumor resection with worse than minor neurofunction impairment
    • Age ≥ 50 years and KPS 70-100% and underwent prior tumor biopsy only
    • Age ≥ 50 years and KPS < 70%
• Underwent most recent brain tumor surgery within the past 5 weeks
• No recurrent or multifocal malignant gliomas
• At least 1 block of tissue available for analysis of MGMT gene methylation status
• No metastases detected below the tentorium or beyond the cranial vault

PATIENT CHARACTERISTICS:

• KPS 60-100%
• Absolute neutrophil count ≥ 1,500 cells/mm^3
• Platelet count ≥ 100,000 cells/mm^3
• Hemoglobin ≥ 10 g/dL (transfusion or other intervention allowed)
• BUN ≤ 25 mg/dL
• Creatinine ≤ 1.7 mg/dL
• Bilirubin ≤ 2.0 mg/dL
• AST and ALT ≤ 3 times normal
• Negative pregnancy test
• Not pregnant or nursing
• Fertile patients must use effective contraception
• No prior invasive malignancy (except for nonmelanomatous skin cancer) unless patient is disease free for ≥ 3 years (e.g., carcinoma in situ of the breast, oral cavity, or cervix allowed)

• No severe, active comorbidity, including any of the following:

  • Unstable angina and/or congestive heart failure requiring hospitalization
  • Transmural myocardial infarction within the last 6 months
  • Acute bacterial or fungal infection requiring intravenous antibiotics at the time of registration
  • Chronic obstructive pulmonary disease exacerbation or other respiratory illness requiring hospitalization or precluding study therapy at the time of registration
  • Known hepatic insufficiency resulting in clinical jaundice and/or coagulation defects
  • Known AIDS based upon current CDC definition
  • Major medical illnesses or psychiatric impairments that, in the investigator's opinion, will prevent administration or completion of protocol therapy
  • Active connective tissue disorders, such as lupus or scleredema that, in the opinion of the treating physician, may put the patient at high risk for radiation toxicity
• No prior allergic reaction to temozolomide

PRIOR CONCURRENT THERAPY:

• See Disease Characteristics
• Recovered from the effects of surgery, postoperative infection, and other complications prior to study entry

• No prior chemotherapy or radiosensitizers (including polifeprosan 20 with carmustine implant [Gliadel wafers] or any other intratumoral or intracavitary treatment) for cancers of the head and neck region

  • Prior chemotherapy for a different cancer is allowed
• No prior radiotherapy to the head or neck (except for T1 glottic cancer) that would result in an overlap of radiation fields
• No treatment on other therapeutic clinical protocols within 30 days prior to study entry or during participation in the study
• No concurrent prophylactic growth factors
• No other concurrent investigational drugs
• No concurrent surgical procedures for tumor debulking
• No other concurrent chemotherapy, immunotherapy, or biologic therapy
• No additional concurrent stereotactic boost radiotherapy
• No concurrent intensity-modulated radiotherapy
• Concurrent steroids allowed provided dose is stable or decreasing in the past 5 days