Stereotactic Body Radiation Therapy in Treating Patients With Inoperable Stage I or Stage II Non-Small Cell Lung Cancer

RATIONALE: Radiation therapy uses high-energy x-rays to damage tumor cells. Stereotactic body radiation therapy may be able to deliver x-rays directly to the tumor and cause less damage to normal tissue. PURPOSE: This phase II trial is studying how well stereotactic body radiation therapy works in treating patients with inoperable stage I or stage II non-small cell lung cancer.