This is an exploratory Phase 1, prospective study assessing the biodistribution and radiation dosimetry of the Positron Emission Tomography [18F]FAraG (VisAcT) in cancer patients selected for immunotherapy. Each patient may have up to two [ 18F]FAraG PET imaging sessions, a baseline image and a post start of immunotherapy image. For each imaging session, patients will receive a single injection of [ 18F]FAraG and undergo up to four whole-body PET scans in the same day. Blood samples may be collected at up to 9 time points post-injection to analyze whole-blood/plasma time activity of [18F]FAraG. Following each imaging session, we will also assess safety in each subject. Blood pressure, heart rate, pulse oximetry, temperature, and respiratory count measurements as well as an electrocardiogram (ECG) recording will be taken prior to imaging, and after whole-body PET scans are completed.