The purpose of this study is to use cone-beam CT scans to more accurately position the tumor during radiation and to see whether this method is more effective than the standard method of using 2D images (portal images), which is a type of X-ray. Cone-beam CT is a type of CT scanner attached to the treatment accelerator that produces 3D images of the patient.

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.

Inclusion Criteria:

• Patients must have histologic proof of a thoracic malignancy, confirmed at MSKCC and suitable for radiation therapy, in order to be eligible for this study.
• Patients must be older than 18 years of age
• At least part of the tumor must be visible as observed in a diagnostic or planning CT. Patients must have Karnofsky Performance Status ≥ 70%

Exclusion Criteria:

• Pregnant Women