DISEASE CHARACTERISTICS:

• Histologically confirmed metastatic brain tumor OR

• Histologically confirmed primary brain tumor

  • Glioblastoma multiforme
  • Anaplastic astrocytoma
  • Anaplastic oligodendroglioma
  • Anaplastic mixed oligoastrocytoma
  • Low-grade glioma
  • Meningioma
  • Ependymoma
• Planned external beam cranial radiotherapy (partial or whole brain) with a total dose of at least 25 Gy in at least 10 fractions of 180-300 cGy each

PATIENT CHARACTERISTICS:

Age:

• 18 and over

Performance status:

• Karnofsky 70-100%

Life expectancy:

• At least 3 months

Hematopoietic:

• WBC ≥ 1,500/mm^3
• Hemoglobin ≥ 10.0 g/dL
• Platelet count ≥ 75,000/mm^3

Hepatic:

• Not specified

Renal:

• Not specified

Cardiovascular:

• No hypertension or other cardiovascular disease requiring antihypertensives and/or other cardiovascular medications

Other:

• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception
• No other serious medical or psychiatric illness that would preclude study participation
• No hypersensitivity to study drug
• No history of steroid psychosis
• No family history of or active Tourette's Syndrome
• No prior or active glaucoma

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• Not specified

Chemotherapy:

• Prior or concurrent chemotherapy allowed

Endocrine therapy:

• Concurrent steroids allowed

Radiotherapy:

• See Disease Characteristics
• Prior radiotherapy allowed except to brain (including stereotactic radiosurgery)
• No concurrent craniospinal axis radiotherapy

Surgery:

• Not specified

Other:

• No prior or concurrent medications for attention deficit disorder, anxiety disorder, schizophrenia, or substance abuse
• No concurrent anti-depressants