Figure 3. PET images in a patient with right hilar cancer illustrating problems with accurate delineation of target volumes based on thresholding of PET images. (A) PET threshold is set at 40% of maximum standard uptake value (SUV) of tumour. (B) PET threshold is set at 30% of maximum SUV. If delineating this tumour using PET alone, different threshold settings would result in different target volumes. Reprinted with permission of the Society of Nuclear Medicine from: Bradley JD, Perez CA, et al. Implementing biologic target volumes in radiation treatment planning for non-small cell lung cancer. J Nucl Med 2004;45:96S–101S.