Abstract

Modern radiotherapy techniques heavily rely on high quality medical imaging. Increased accuracy to deliver the dose to tumors while sparing normal tissues demands more precise delineation of the tumors. When considering to deliver a boost to more aggressive parts of tumors, intratumoral heterogeneity needs to be assessed accurately. Adaptive radiotherapy demands evaluation of response during the course of radiotherapy, interms of both volumetric and functional changes.Besides depicting anatomy, the role of functional and molecular imaging is therefore becoming increasingly important. Besides functional MRI , molecular imaging with positron emission tomography (PET) is rapidly evolving. PET provides biological information about the tumor, complementary to anatomical imaging. Integrated PET -CT has already found its way into the practice of radiation oncology. For this purpose, F-18-fluorodeoxyglucose (FDG) is the most important radiopharmaceutical, e.g. in radiotherapy planning and follow-up. The PET -derived information augments accurate delineation of radiotherapy target volumes and treatment of the tumor and its extensions, while reducing the dose to surrounding healthy tissues. In addition to FDG , other PET tracers are available for imaging more specific biological tumor characteristics, that play a pivotal role in radiation resistance. Using tracers that depict proliferation such as F-18 fluorthymidine or hypoxia such as F-18 fluorinated imidazoles, the role of PET beyond FDG for patient selection, treatment modification and adaptation and early response monitoring are explored.