For NSCLC, F-18 FDG-PET scans allow more thorough staging, thus avoiding unnecessary treatments. It reduces radiation treatment volumes because of the avoidance of mediastinal lymph nodes that are PET negative and hence reduces toxicity with the same radiation dose or enables radiation dose escalation with the same toxicity. Further research is needed to assess the effect of PET on survival. PET also reduces interobserver variability for delineating tumors and opens perspective for more automated delineation parts in radiation planning. F-18 FDG-PET-CT scans can already at present be used in routine clinical practice. It is of paramount importance that the necessary calibrations have been done and that strictly standardized protocols for every step in the treatment and planning chain are implemented. For the delineation of target volumes, a combination of PET-CT images, auto-delineation tools, and last not but least manual editing of the target volumes is necessary. The latter is needed because of resolution deficiencies of PET and any other imaging modality as well as the incorporation of other that image information (e.g., know patterns of tumor spread according to pathological studies, knowledge of endoscopic findings, and other tumor and patient factors) to come to target volume definitions that have proven their clinical efficacy.