DISEASE CHARACTERISTICS: Histologically or cytologically confirmed non-small cell lung cancer (NSCLC) Stage IIIB or bulky stage IIIA not amenable to surgical resection Medically inoperable stage II or non-bulky stage IIIA Locally recurrent disease following surgery that is not amenable to further surgical resection No small cell carcinoma or mixed cytology No disease beyond radiation portal (T4 tumors with documented multifocal malignant pleural involvement or extension of supraclavicular nodal disease to cervical chain) No pleural effusion Pleural effusions visible on CT scan but not on chest x-ray that are inaccessible to thoracentesis or are cytologically negative are allowed Ineligible for enrollment on protocol RTOG 93-09

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-2 Karnofsky 50-100% Life expectancy: Not specified Hematopoietic: Absolute neutrophil count at least 2,000/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than 1.5 mg/dL No known Gilbert's disease Renal: Creatinine no greater than 1.5 mg/dL Calcium less than 12.0 mg/dL Cardiovascular: No symptomatic cardiovascular disease No active angina No congestive heart failure requiring active therapy No uncontrolled arrhythmias No myocardial infarction within the past 6 months Pulmonary: FEV1 at least 1.0 L unless cleared by radiation oncologist Other: Not pregnant Negative pregnancy test Fertile patients must use effective contraception for 3 months before study, during study, and for 3 months after study HIV negative No other concurrent active or invasive malignancy except nonmelanoma skin cancer Less than 10% unintended weight loss within 3 months of diagnosis No other concurrent medical condition that would preclude study No social situation or psychiatric disorder that would preclude study No active or uncontrolled infection No history of seizures No uncontrolled diabetes mellitus (random blood sugar at least 250 mg/dL)

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No prior chemotherapy for NSCLC No prior irinotecan or topotecan Endocrine therapy: Not specified Radiotherapy: No prior radiotherapy for NSCLC No prior radiotherapy to the chest Surgery: See Disease Characteristics Other: No concurrent phenytoin, phenobarbital, or other antiepileptic prophylaxis