This pilot study aims to evaluate the test-retest variability of \[18F\]F-AraG-PET imaging in patients with advanced NSCLC tumors. The main objectives of the study are to quantify the uptake of \[18F\]F-AraG in tumors and lymphoid tissue in two consecutive scans spaced not longer than 7 days apart from each other to estimate the magnitude of physiologic and measurement variability. To explore these objectives, eligible subjects will undergo two \[18F\]F-AraG PET/CT scans within 7 days of each other prior to receiving treatment. This study is a single-site, open-label, non-randomized, single-arm pilot trial. Patients and care providers will not be blinded to any part of the study.