Use of [18F]FDG PET/CT for Target Volume Definition in Radiotherapy

Addition of spatial biological information, provided by 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography ([18F]FDG PET/CT) imaging, is recommended for target volume delineation in solid tumours originating in, e.g., the head-and-neck region, lung, oesophagus, uterus, cervix, and lymphoma. Standardised patient preparation, as well as standardised acquisition and reconstruction of the PET-images are mandatory. Patient positioning and alignment should be performed using lasers and immobilising devices, and images are preferable acquired in radiotherapy position. Correction for respiratory motion should be considered and performed by motion-encompassing, controlled breathing, respiratory gating or data-driven gating. These motion-corrections should match the mitigation methods used for radiotherapy planning and treatment delivery. The success of PET-guided target volume delineation depends mainly on the performed segmentation technique, in which we distinguish manual, semi-automatic or automatic segmentation methods. Manual segmentation has the largest interobserver variability and automatic segmentation can be optimised by consensus algorithms. Despite promising results of automatic segmentation methods, none are currently applicable in all clinical settings. Therefore, results should always be verified by an expert. Despite feasibility and advantages observed in planning studies, the clinical level of evidence for [18F]FDG PET/CT-guided treatment planning and dose delivery is still limited to a few indications.