DISEASE CHARACTERISTICS:

• Histologically confirmed* low-grade glioma, including any of the following:

  • Juvenile pilocytic astrocytoma (JPA) or pleomorphic JPA

  • Diffuse astrocytoma, including any of the following subtypes:

    • Fibrillary astrocytoma
    • Gemistocytic astrocytoma
    • Subependymal giant cell astrocytoma
    • Pleomorphic xanthoastrocytoma
  • Low-grade oligoastrocytoma
  • Low-grade oligodendroglioma
  • Low-grade glioma not otherwise specified NOTE: *Patients with chiasmatic lesions who have contiguous extension of tumor into other regions of the visual pathway by CT scan or MRI are eligible without histopathologic confirmation; repeat biopsy required for patients with recurrent tumors that enhance but whose initial tumor did not
• Measurable disease by radiography

• Meets any of the following criteria:

  • Progressive nonresectable disease

    • Any location in the brain
  • Patients with a less than gross total resection are eligible provided they are symptomatic from their tumor OR the risk from neurologic impairment with progression is high enough to warrant immediate treatment
  • Has undergone biopsy only

• Must have received ≥ 1 course of prior chemotherapy (for patients < 10 years of age)

  • Prior chemotherapy optional (for patients ≥ 10 years of age)
• No type-1 neurofibromatosis
• No evidence of leptomeningeal dissemination

PATIENT CHARACTERISTICS:

Age

• 3 to 20

Performance status

• ECOG 0-2 OR
• Karnofsky 50-100% (for patients > 16 years of age) OR
• Lansky 50-100% (for patients ≤ 16 years of age)

Life expectancy

• At least 1 year

Hematopoietic

• Absolute neutrophil count ≥ 1,000/mm^3
• Platelet count ≥ 100,000/mm^3 (transfusion independent)
• Hemoglobin ≥ 10.0 g/dL (transfusions allowed)

Hepatic

• Not specified

Renal

• Not specified

Other

• Not pregnant
• Negative pregnancy test
• Fertile patients must use effective contraception
• Not in status epilepticus, coma, or requiring assisted ventilation prior to study entry
• Patients with a seizure disorder are eligible provided they are on anticonvulsants AND disease is well controlled

PRIOR CONCURRENT THERAPY:

Biologic therapy

• Not specified

Chemotherapy

• See Disease Characteristics
• Recovered from prior chemotherapy
• No concurrent chemotherapy

Endocrine therapy

• Concurrent dexamethasone allowed provided patient has been on a stable dose for ≥ 2 weeks prior to study entry
• Concurrent dexamethasone allowed for symptoms of increased intracranial pressure

Radiotherapy

• No prior radiotherapy

Surgery

• See Disease Characteristics

Other

• No other concurrent anticancer therapy