Brief Summary: Little is known about the safety of body radiation therapy (SBRT), especially the impact on pulmonary function, quality of life, and on functional changes within the lung itself. Radiation dose constraints and capturing functional changes on imaging are not well studied in this setting. The current study aims to evaluate the utility of advanced imaging to measure lung function prior to and after treatment and to assess the feasibility of using this data to adapt SBRT planning.

Detailed Description: Stereotactic body radiation therapy (SBRT) is becoming a new standard for unresectable lung metastases and primary lung cancers. However, it is becoming increasingly common for patients to undergo multiple courses of lung SBRT to synchronous and/or metachronous lung lesions. Further, the indications for SBRT are being expanded to patients who have very poor pulmonary function such as FEV1 \< 0.5 L or DLCO \< 35% predicted, who have large tumors (\>3 cm), or who have centrally located lesions that abut great vessels and mainstem bronchi. Little is known about the safety of such treatments, especially the impact on pulmonary function, quality of life, and on functional changes within the lung itself. Radiation dose constraints and capturing functional changes on imaging are not well studied in this setting. The current study aims to evaluate the utility of advanced imaging to measure lung function prior to and after treatment and to assess the feasibility of using this data to adapt SBRT planning. SPECT/CT will be used to measure ventilation and perfusion changes while. CT ventilation scans will be used to correlate functional changes observed on diagnostic SPECT/CT. Dynamic contrast enhanced MRI (DCE-MRI) will also be used to explore local vascular changes in the treated tumor. In patients whose tumors lie close to the heart, cardiac MRI will be used to investigate whether high doses of radiation per fraction are associated with changes in cardiac function. These imaging modalities may be used to potentially predict toxicity and patient response with the ultimate goal of prospectively adapt dose to individual patient and tumor characteristics. Lung function prior to and post-treatment will also be measured as a correlate of functional imaging changes. Identifying areas of the lung that are sub-functional or low-functioning may offer an opportunity to adapt stereotactic ablations that spare functional lung thereby making SBRT treatments to higher risk patients safer.