Developments in medical imaging over the past 2 decades are providing significant improvement in tumor definition. Improvements in soft tissue visualization with tumor specific contrast combined with direct 3D data acquisition and millimetre spatial resolution set new standards in tumor definition. Such precision in tumor imaging provides a new level of challenge for precision radiation treatment. Significant further improvement over the next decade in geographic definition is unlikely. The challenge for imaging research is that of extracting tissue specific information about tumors such as perfusion and response to therapy rather than simply anatomical clarity.