The ability to eliminate the tumor with radiation depends in part on the accuracy of delivering the radiation to the lung. The position of the tumor changes because of normal breathing. Therefore, we want to improve the accuracy of the way the radiation is delivered to the tumor. With cone-beam CT scans taken before and during your treatment, we will be able to determine the location of the tumor with 3D images, measure how much the tumor moves as you breathe, and then position you so that the tumor will get the best delivery of radiation.