PRIOR CONCURRENT THERAPY: Biologic therapy: At least 3 weeks since prior biologic therapy and recovered No concurrent biologic therapy Chemotherapy: See Disease Characteristics No more than 1 prior chemotherapy regimen At least 3 weeks since prior chemotherapy (6 weeks for nitrosoureas) and recovered No prior interstitial chemotherapy such as Gliadel wafer implantation for present brain tumor No concurrent chemotherapy Endocrine therapy: At least 3 weeks since prior hormonal therapy and recovered No concurrent hormonal therapy Radiotherapy: See Disease Characteristics No prior brachytherapy for present brain tumor At least 3 months since other prior radiotherapy and recovered No concurrent radiotherapy Surgery: See Disease Characteristics No prior radiosurgery for present brain tumor At least 3 weeks since other prior oncologic surgery No other concurrent oncologic surgery Other: No other concurrent investigational drugs