DISEASE CHARACTERISTICS: Histologically confirmed recurrent or refractory glioblastoma multiforme, gliosarcoma, anaplastic astrocytoma, anaplastic oligodendroglioma, anaplastic oligoastrocytoma (mixed glioma), anaplastic pleomorphic xanthoastrocytoma, or malignant dedifferentiation from prior low grade glioma Tumor in first relapse Measurable disease by MRI scan Enhancing lesion amenable to gross total resection Postoperative resection cavity not communicating freely with ventricular system

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Karnofsky 60-100% Life expectancy: Greater than 8 weeks Hematopoietic: Absolute neutrophil count greater than 1,000/mm3 Hemoglobin greater than 10.0 g/dL Platelet count greater than 100,000/mm3 Hepatic: Bilirubin less than 1.5 times upper limit of normal (ULN) SGOT or SGPT less than 2.5 times ULN Renal: Not specified Other: Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception HIV negative No AIDS-related illness No other malignancy within past 5 years, except: Basal or squamous cell carcinoma of the skin Carcinoma in situ of the cervix No psychological, familial, sociological, or geographical conditions that would interfere with study compliance No active infection requiring systemic antibiotics No nonmalignant systemic disease considered to increase medical risk

PRIOR CONCURRENT THERAPY: Biologic therapy: No concurrent biologic therapy Chemotherapy: At least 4 weeks since prior chemotherapy (6 weeks since nitrosoureas or mitomycin) and recovered No prior polifeprosan 20 with carmustine implant (Gliadel wafers) Prior adjuvant chemotherapy allowed No other concurrent chemotherapy Endocrine therapy: Patient on stable steroid therapy for at least 2 weeks prior to study No concurrent hormonal agents Radiotherapy: Prior radiosensitization allowed and recovered Prior external beam radiotherapy required and recovered No concurrent radiotherapy (including palliative) Surgery: Prior surgery or biopsy required and recovered Other: No prior iodine I 125 seed implants Concurrent alternative therapy allowed No other concurrent antineoplastic therapy No other concurrent investigational drugs