DISEASE CHARACTERISTICS:

Histologically confirmed brain tumor including but not limited to the following: Anaplastic astrocytoma, Glioblastoma multiforme, Low-grade glioma, Ependymoma, Medulloblastoma, Pineal tumors, Chiasmal glioma, Craniopharyngioma, Brain stem glioma (requirement for histologic diagnosis may be waived).

Disease refractory to standard therapy or no standard chemotherapy exists and ineligible for potential curative surgery or radiotherapy.

Measurable or evaluable disease on radiographic studies with evidence of progression on prior chemotherapy or radiotherapy or persistent disease after surgery.

PRIOR/CURRENT THERAPY:

See Disease Characteristics

At least 6 months since carboplatin.

At least 3 weeks since myelosuppressive therapy.

Patients who received stem cell or bone marrow rescue after nitrosourea therapy are eligible after 3 weeks if they have recovered from hematologic toxicities of their prior therapy.

Concurrent steroids allowed if dose stable for at least 2 weeks prior to entry.

Recovered from toxic effects of any prior therapy.

PATIENT CHARACTERISTICS:

Age: 21 and under.

Performance status: ECOG 0-2.

Life expectancy: At least 8 weeks.

HEMATOLOGIC:

Absolute granulocyte count greater than 1,500/mm(3).

Platelet count greater than 100,000/mm(3) (at least 75,000/mm(3) in patients with prior bone marrow transplantation or craniospinal irradiation).

Hemoglobin greater than 8.0 g/dL.

HEPATIC:

Bilirubin no greater than 2 times normal.

ALT no greater than 2 times normal.

RENAL:

Creatinine within normal limits for age as follows:

Age (in years) -- Creatinine (in mg/dL):

Younger than 5 -- no greater than 1.2;

5-10 -- no greater than 1.5;

10-15 -- no greater than 1.8;

Older than 15 -- no greater than 2.4.

OTHER:

No significant systemic illness.

No pregnant or nursing women.

Negative pregnancy test required of fertile women.

Effective contraception required of fertile patients.

Durable power of attorney required of all patients 18-21 years of age.