Traditional imaging techniques, such as computed tomography (CT), have high spatial resolution for changes in the anatomy or structure of organs, but are not very useful for detecting early biochemical changes. Conversely, positron emission tomography (PET) relies on changes in molecular biology to identify the earliest stages of disease but, if used alone, has sub-optimal spatial delineation. However, computer-assisted fused-image and/or single-machine integrated PET-CT can show early biochemical changes with improved anatomic resolution, often before there is any structural change. This approach enables the clinician to view and assess the patient?s body from a biochemical perspective. In an era of rapidly evolving 3D conformal radiation treatment, accurate target delineation is a crucial factor in optimization of clinical results. This paper reviews some of the basic-science underpinnings of PET-CT, and highlights some important findings in the early clinical work thus far performed.

Key words: PET-CT; 3D radiation therapy.