DISEASE CHARACTERISTICS:

• Pathologically confirmed low grade residual astrocytomas or other eligible residual tumors of the brain interpreted as low grade (WHO grades I and II) such as the following:

  • Glial Tumors

    • Astrocytic tumors

      • Low grade astrocytoma (variants: fibrillary, protoplasmic, gemistocytic)
      • Pilocytic astrocytoma
      • Pleomorphic xanthoastrocytomas
      • Subependymal giant cell astrocytoma
      • Infantile desmoplastic astrocytoma

    • Low grade oligodendroglial tumors

      • Low grade oligodendroglioma

    • Low grade mixed gliomas

      • Oligo-astrocytoma

  • Neuronal Tumors

    • Ganglioglioma (excluding tumors with anaplastic astrocytic components)
    • Infantile desmoplastic ganglioglioma
  • Chiasmatic-hypothalamic tumor without histologic confirmation
• All of the following diagnostic tests (radiological or clinical evidence of progression, surgery, or confirmatory MRI) must be carried out within 6 weeks of enrollment into this study
• Progressive disease following surgical excision based on clear radiological or clinical evidence of progression, or an incomplete excision (less than 95% or greater than 1.5 cm2) with necessity to begin treatment because of a risk of neurologic impairment with progression
• Chiasmatic lesions that have contiguous extensions of tumor into other regions of the visual pathways demonstrated on contrast MRI will be eligible for study without histopathological confirmation
• Patients with neurofibromatosis who have radiographic diagnosis of chiasmatic-hypothalamic tumor are eligible for the study, without requiring a biopsy confirmation of tumor histology, but not unless tumor progression is documented radiographically
• No intrinsic brain stem tumors of the pons or isolated optic nerve tumors without definitive involvement of the optic chiasm

PATIENT CHARACTERISTICS:

Age:

• Under 10

Performance status:

• Not specified

Life expectancy:

• Not specified

Hematopoietic:

• Absolute neutrophil count greater than 1,000/mm^3 (arm II)
• Platelet count greater than 100,000/mm^3 (arm II)

Hepatic:

• Not specified

Renal:

• Creatinine less than 1.5 times upper limit of normal for age OR
• Creatinine clearance or radioisotope GFR greater than 70 mL/min or equivalent GFR as determined by the institutional normal range

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• Not specified

Chemotherapy:

• No prior chemotherapy for the tumor

Endocrine therapy:

• Prior corticosteroid therapy allowed

Radiotherapy:

• No prior radiotherapy for the tumor

Surgery:

• See Disease Characterisitcs

Other:

• Prior diuretic therapy allowed