DISEASE CHARACTERISTICS:

• Histologically confirmed* low-grade glioma, including 1 of the following subtypes:

  • Astrocytoma variants

    • Fibrillary, protoplasmic, or mixed
  • Pilocytic astrocytoma, including pilomyxoid variants
  • Pleomorphic xanthoastrocytoma
  • Infantile desmoplastic astrocytoma
  • Ganglioglioma
  • Oligodendroglial tumors
  • Mixed glioma, including oligoastrocytoma NOTE: *Biopsy not required for patients who have visual pathway tumors involving the optic nerves and/or optic radiations (i.e., not isolated to the hypothalamus/chiasm)

• Biopsy proven focal low-grade gliomas of the brainstem with measurable disease allowed

  • No diffuse, intrinsic brainstem tumors
• Residual tumor visible on MRI

• Patients without NF-1 must meet the following criteria:

  • Progressive disease after surgery/biopsy based on clear radiographic or clinical evidence of progression OR gross residual tumor (> 1.5 cm²) after surgery/biopsy that is felt to be a high risk to the patient for neurologic and/or visual impairment if the tumor progresses
  • Visual pathway tumors that are not isolated to the hypothalamus/chiasm and are not biopsied must be a high risk to the patient for neurologic and/or visual impairment
• Patients with NF-1 must have evidence of radiographic progression on MRI and/or clinical worsening (e.g., worsening of ophthalmologic exam for visual pathway tumors)

• Meets 1 of the following criteria:

  • Newly diagnosed disease
  • Recurrent disease
• No ventriculoperitoneal shunt-related ascites

PATIENT CHARACTERISTICS:

• Karnofsky performance status (PS) 50-100% (for patients > 10 years of age) OR Lansky PS 50-100% (for patients ≤ 10 years of age)
• Absolute neutrophil count ≥ 1,000/mm³
• Platelet count ≥ 100,000/mm³ (transfusion independent)
• Hemoglobin ≥ 8.0 g/dL (RBC transfusions allowed)

• Creatinine clearance or radioisotope glomerular filtration rate ≥ 70 mL/min OR creatinine based on age, as follows:

  • No greater than 0.8 mg/dL (for patients ≤ 5 years of age)
  • No greater than 1.0 mg/dL (for patients 6-10 years of age)
  • No greater than 1.2 mg/dL (for patients 11-15 years of age)
  • No greater than 1.5 mg/dL (for patients > 15 years of age)
• Bilirubin ≤ 1.5 times upper limit of normal
• ALT ≤ 110 U/L
• Albumin ≥ 2 g/dL
• No history of allergy to carboplatin
• No hyponatremia requiring treatment
• No uncontrolled infection
• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

• See Disease Characteristics
• No prior therapy except for corticosteroids and surgery (for patients with newly diagnosed disease)
• Prior chemotherapy and/or radiotherapy in addition to surgery and corticosteroids allowed (for patients with recurrent disease)
• Prior carboplatin and/or vinblastine allowed if there was no evidence of progressive disease while on therapy and there were no dose reductions due to toxicity (for patients with recurrent disease)
• At least 3 weeks since prior myelosuppressive chemotherapy (6 weeks for nitrosoureas) and recovered (for patients with recurrent disease)
• At least 7 days since prior hematopoietic growth factors (for patients with recurrent disease)
• At least 7 days since prior biological agents (for patients with recurrent disease)
• At least 9 months since prior external beam radiotherapy or gamma knife therapy that included all target lesions (i.e., there is no restriction if a new lesion arises outside the radiation field or a nonirradiated lesion progresses) and recovered (for patients with recurrent disease)
• No other concurrent investigational drugs
• No other concurrent anticancer agents
• No other concurrent chemotherapy, radiotherapy, immunotherapy, or biological therapy
• No concurrent corticosteroids for antiemesis
• Concurrent steroids allowed for tumor edema/increased intracranial pressure provided dose of dexamethasone is stable or decreasing for the past 7 days
• Concurrent physiologic or stress doses of steroids allowed for endocrine deficiencies