Theragnostic imaging for radiation oncology : dose - painting

112 http://oncology.thelancet.com Vol 6 February 2005 Diagnostic imaging, from radiographs to CT, has been used throughout the history of radiotherapy to define the site to which the radiation should be delivered for patients with cancer. Theragnostic imaging is a method by which the radiation dose can be delivered in the four dimensions of space and time to achieve the optimum outcome after radiotherapy. What does theragnostic imaging mean? From the Greek words therapeia (to treat medically) and gnosis (knowledge) theragnostic imaging refers to the use of information from medical images to determine how to treat individual patients. Rapid technological and scientific progress in molecular and functional imaging, in radiotherapy planning and delivery, and in clinical radiation biology is making radiotherapy guided by theragnostic imaging a realistic goal. Molecular imaging is providing new research opportunities in the preclinical and clinical development of new therapies and in the study of small-animal models of human disease. To take full advantage of the curative potential of modern, high-precision radiotherapy, high-quality imaging is needed for identification of target volumes. Conversely, optimum use of the spatial information provided by molecular imaging requires radiotherapy; radiation is a therapeutic agent that can be modulated in the four dimensions of space and time, and the dose can be precisely defined to produce a specified local effect of a given magnitude. This review explores the latter perspective.