This study is the first report, to our knowledge, on dynamic imaging and kinetic modeling of [18F]F-AraG, as well as being the first-in-human report on using [18F]F-AraG in a non–small cell lung cancer (NSCLC) patient undergoing anti–PD-1 immunotherapy, aiming to enhance our understanding of its potential quantitative utility in predicting immunotherapy response, as well as its wider application in other disease conditions. The gene discussed is PDCD1; the disease is lung cancer.