To validate a new 4D Cone Beam CT (4DCBCT) reconstruction algorithm that was developed in our research group recently in terms of its geometry and intensity accuracy through real patient studies. Dose calculation found out in this study will not be used on the subject

Before patient studies, we will have conducted experimental studies on a lung phantom.

The purpose of this step is to comprehensively evaluate the system performance and gain confidence prior to its applications to real patient cases. We will operate the phantom to simulate motion patterns with different motion amplitude/frequency. 4DCBCT images will be reconstructed using our method and the conventional FDK algorithm. The validation will focus on two aspects: HU value accuracy and anatomy location accuracy.

Imaging dose in these scans will be also measured in phantom studies to make sure the radiation dose level is acceptable for patient studies. adiation dose level is acceptable for patient studies.

After testing the reconstruction algorithm on phantoms, we will move on to real patient cases. We will conduct patient studies on lung cancer patients treated under Image Guided Radiation Therapy (IGRT) at Department of Radiation Oncology, UT Southwestern Medical Center. CBCT projection data will be collected (4 gantry rotations, each within 1 minute) in only one treatment fraction. 4DCBCT images will be reconstructed from the current standard FDK algorithm using all the projection data, and from our system using data only in the first gantry rotation. Patient 4DCT image will also be used, which have been acquired during treatment planning stage per standard treatment protocol at UTSW.

The image quality of our 4DCBCT will be assessed in two aspects:

1) geometry accuracy, by comparing selected anatomical landmark locations with those in 4DCBCT reconstructed by the FDK algorithm. 2) HU accuracy, by comparing HU values in selected regions of interest (ROIs) with those in 4DCT.

The 4DCT images will be extracted from radiation therapy information system MOSAIQ.

The CBCT projection data will be exported from a computer that controls the image acquisition system

Inclusion Criteria:

1. Patients that have been diagnosed with lung cancer, and are treated at Department of Radiation Oncology, UTSW.
2. Patients are greater than 18 years of age.
3. Patients understand a written informed consent document and are willing to sign the consent form.

Exclusion Criteria:

1. Women who are pregnant or trying to get pregnant
2. Children (under age of 18)

Patients will be identified by physician co-investigator during CT-simulation stage. One of the investigators or research coordinators will verbally explain the study to the patient.

It will be clearly explained that patient's treatment will not be modified based on the data collected in this study. If the patient agrees to participate, an informed consent form will be signed by both the patient and the investigator/research coordinator and a copy of the signed form will be given to the patient. All of the key investigators and research coordinators in this project are experienced in clinical studies and clinical trials and have undergone appropriate protection of human research subjects training and HIPAA training.