This phase I trial studies the best dose of radiation therapy in treating patients with locally advanced non-small cell lung cancer that cannot be removed by surgery. Radiation therapy uses high energy x rays to kill tumor cells. Specialized radiation therapy, such as stereotactic body radiation therapy (SBRT), that delivers a high dose of radiation directly to the tumor may kill more tumor cells and cause less damage to normal tissue. SBRT has been shown to provide excellent results when used in early stage lung cancer, but has not yet been applied to patients with more advanced disease.