The purpose of this study is to determine whether an imaging scan called a Sodium Fluoride Cardiac PET/MRI (18F-NaF PET/MRI) can detect early injury to heart blood vessels (coronary arteries) in patients with stage II-IV cancer who have increased risk of cardiovascular dysfunction after treatment with radiation therapy near the heart. Radiation therapy is an important part of treatment for many cancers, but it can cause some unwanted consequences such as cardiac dysfunction, coronary artery disease, and heart failure. 18F-NaF PET/MRI is a type of imaging scan that is injected to help take a detailed picture to potentially identify high-risk coronary artery plaques or areas of injury. Study procedures include a 18F-NaF cardiac PET/MRI scan and coronary computed tomography angiogram (CT with iodinated contrast to look at heart blood vessels). Researchers hope that by using 18F-NaF Cardiac PET/MRI imaging, they can sooner identify patients at risk of serious cardiac dysfunction earlier after radiation therapy, resulting in better outcomes. The use of 18F-NaF PET/MRI in this study is experimental.