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