The Use of PET for Radiotherapy

The rapidly growing field of PET imaging is providing new opportunities to define target volumes for radiotherapy. For multiple disease sites, PET has become a tool to provide a way to locate the most rapidly metabolizing portions of the lesion mass and to detect unsuspected metastases over conventional CT imaging. This made PET a desirable imaging modality for radiotherapy treatment planning. In addition to improved staging and target definition, radiotherapy has benefitted from the use of PET as a therapy response tool. Introduction of combined PET/CT units has accelerated the proliferation of PET into treatment planning. Today there are many radiation therapy departments either has a PET scanner of their own or access to PET images. We are, now, in the era of solving problems of PET imaging for smooth integration into radiotherapy. However, in the future we will be beyond hyper-metabolic tissue characterization and incorporation of this information into functional treatment planning. New lesion markers under development in animal models today will inevitably be translated into clinical studies. With advances in computer and biotechnology, in the near future, it may be possible to give a cocktail of tracers to patients so as to generate multi-dimensional information, to further improve the radiobiological characterization of the target volume for consideration in the radiation treatment planning. This review provides an introduction to the subject of the use of PET for radiotherapy for clinicians. It also outlines today's and tomorrows challenges for successful integration of PET imaging into radiotherapy.