PRIOR CONCURRENT THERAPY: Biologic therapy: At least 4 weeks since prior biologic therapy and recovered Chemotherapy: At least 4 weeks since prior chemotherapy and recovered No prior mitomycin, irinotecan, or nitrosoureas No more than 6 courses of chemotherapy containing an alkylating agent No more than 4 courses of carboplatin Endocrine therapy: At least 4 weeks since prior endocrine therapy and recovered Radiotherapy: At least 4 weeks since prior radiotherapy and recovered No prior radiotherapy to more than 20% of bone marrow No prior whole pelvis radiotherapy Surgery: Not specified Other: No concurrent phenytoin, phenobarbital, valproic acid, or other antiepileptic prophylaxis No concurrent warfarin