DISEASE CHARACTERISTICS:

• Histologically confirmed recurrent supratentorial glioblastoma multiforme, anaplastic astrocytoma, or gliosarcoma
• Must be able to undergo surgical resection
• At least 1 bidimensionally measurable lesion documented on Gd-MRI within 72 hours after surgical implantation of Gliadel wafers
• Not requiring immediate radiotherapy

PATIENT CHARACTERISTICS:

Age:

• 18 and over

Performance status:

• Karnofsky 70-100%

Life expectancy:

• Greater than 12 weeks

Hematopoietic:

• Absolute neutrophil count at least 1,500/mm^3
• Platelet count at least 125,000/mm^3
• Hematocrit at least 29%

Hepatic:

• Bilirubin less than 1.5 times upper limit of normal (ULN)
• SGOT or SGPT less than 2.5 times ULN
• Alkaline phosphatase less than 2 times ULN

Renal:

• BUN less than 1.5 times ULN
• Creatinine less than 1.5 times ULN

Neurological:

• Must be neurologically stable

Other:

• HIV negative

  • No AIDS-related illness
• No nonmalignant systemic disease that would make patient a poor medical risk
• No acute infection requiring intravenous antibiotics

• Not pregnant or nursing

  • Negative pregnancy test 24 hours prior to study
• Effective contraception required of all fertile patients

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• Not specified

Chemotherapy:

• No prior irinotecan
• At least 6 weeks since chemotherapy unless there is unequivocal evidence of tumor progression after chemotherapy

Endocrine therapy:

• At least 1 week of nonincreasing dose of steroids prior to study

Radiotherapy:

• At least 6 weeks since radiotherapy unless there is unequivocal evidence of tumor progression after radiotherapy
• No concurrent radiotherapy

Surgery:

• Not specified