The use of positron emission tomography (PET) in determination of functional tumour volume may pose two major problems especially for the exact delineation of tumour contours:
* Respiratory movements, when the tumour is thoracic, may induce an overestimation
* The PET's low spatial resolution, linked to the emission of photons
The usual method to define tumour contours result of three types of delineation usually used: the visual contouring, the segmentation based on an activity threshold fixed, and the segmentation with adaptive thresholding.
