Recent years have witnessed rapid increase in positron emission tomography (PET) use for diagnosis, staging and restaging of different cancers types. A recent national review concluded that PET scans were associated with changing treatment plans in more than one third of the patients. For instance, FDG-PET, a glucose metabolism analog, is frequently used for radiotherapy target definition and monitoring of treatment response. However, its role in lung cancer, one of the most lethal diseases, is limited by respiratory motion artifacts. In this work, we summarize the latest developments to mitigate these effects and present potentials for future directions.