The trial aims to evaluate the utility of 18FDG-PET/CT in SBRT planning for NSCLC with particular emphasis on the definition of macroscopic and microscopic boundaries of malignant growth. Studies indicate that the definition of the gross tumor volume may gain in quality when CT and 18FDG-PET are combined. In about 30-60% of NSCLC patients considered for radiotherapy, alteration of CT-based treatment volumes is the consequence of a supplementary 18FDG-PET scan. Studies examining the effect of combined PET/CT scans on the delineation of the GTV generally show reduced intra- and inter-clinician variability. Whether this higher degree of consistency is an actual improvement remains to be proven. Pathological specimens from operated NSCLC patients may serve as a gold standard in this respect. To meet the need for tight margins, the clinical target volume in SBRT planning is generally presumed to correspond to the GTV. Whether this clinical practice rests on firm ground is also an issue that can be addressed in a PET-CT-pathology correlation study.