Brain Irradiation in Treating Patients With Limited-Stage Small Cell Lung Cancer

DISEASE CHARACTERISTICS: * Histologically or cytologically confirmed small cell lung cancer by fine needle aspiration, biopsy, or 2 positive sputa * Limited stage (I-IIIB) * Confined to 1 hemithorax * No T4 based on malignant pleural effusion, or N3 disease based on contralateral hilar or contralateral supraclavicular involvement * Complete response after induction chemotherapy (with or without thoracic radiotherapy) * Consolidative chest radiotherapy may be initiated before study * No radiographic evidence of any of the following: * Brain metastases * Normal brain CT scan or MRI less than 1 month before study * Ipsilateral lung metastases * Malignant pleural effusion * Minimal pleural effusion by chest CT scan allowed, but not by chest x-ray PATIENT CHARACTERISTICS: Age * Not specified Performance status * Zubrod 0-1 Life expectancy * Not specified Hematopoietic * Absolute granulocyte count at least 1,500/mm\^3 * Platelet count at least 75,000/mm\^3 * Hemoglobin at least 10.0 g/dL\^ Hepatic * Not specified Renal * Not specified Pulmonary * See Disease Characteristics Other * Not pregnant or nursing * Fertile patients must use effective contraception * Neurological function class 1 or 2 * No epilepsy requiring permanent oral medication * No other malignancy within the past 5 years except nonmelanoma skin cancer or carcinoma in situ of the cervix * No other serious medical or psychiatric condition that would preclude study participation PRIOR CONCURRENT THERAPY: Biologic therapy * Not specified Chemotherapy * See Disease Characteristics * At least 1 week since prior chemotherapy * No concurrent chemotherapy Endocrine therapy * Not specified Radiotherapy * See Disease Characteristics * No prior external beam radiotherapy to the head or neck, including stereotactic radiotherapy * Concurrent thoracic radiotherapy allowed Surgery * Not specified Other * No concurrent antitumor agents