Experimental evaluation of functional imaging for radiotherapy

Functional imaging for radiotherapy is expected to provide diagnostic as well as prognostic information, to monitor treatment, to help stratification of patients for specific therapeutic interventions and to guide dose-painting. During the last years radiotracer-based functional imaging with positron emission tomography (PET), mainly using the glucose analogue [18F]2-fluoro-2-deoxy-D-glucose ([18F]FDG), has been widely implemented in radiotherapy for a more accurate staging and an improved target volume definition in a variety of tumor types. While the technology for integration of functional imaging into clinical radiotherapy is increasingly available, the biological implications for radiation response are poorly understood. Importantly, biomarker development needs to account for the specific parameters known to determine the results of curative radiotherapy. Clinical as well as preclinical studies are necessary to exploit the potential of functional imaging to improve outcome after radiotherapy. In the following sections recent findings from experimental studies using xenotransplanted tumors in nude mice carried out in our laboratories are briefly summarized. (orig.)