DISEASE CHARACTERISTICS: Histologically confirmed stage IIIA non-small cell lung cancer that has been completely resected by lobectomy, bilobectomy, pneumonectomy, or sleeve lobectomy through any incision (thoracoscopic or video assisted resection is acceptable) No known residual disease present Involvement in N2 nodes must have been determined only at the time of surgical exploration or by postoperative pathologic diagnosis All grossly involved nodes must be removed at surgery No positive mediastinoscopy (if lymph nodes on CT scan are greater than 1.5 cm in diameter, mediastinoscopy is required)