Real-time optical surface monitoring data will be acquired from 44 human patients with primary or metastatic lung lesions during and after their 4DCT scan (standard-of-care at our institution). A patient-specific 4D model will be developed using the raw 4DCT projections time-correlated with real-time surface monitoring. In addition, before delivering each dose fraction (3 - 5 for lung SBRT), we will acquire three 15s kV fluoroscopic image acquisitions, time-correlated with optical surface monitoring. The acquisitions will be distributed over three well-spaced beam angles, e.g., every 4th angle for a 12-field plan.