Imaging of tumor physiology: impacts on clinical radiation oncology

As the metabolic microenvironment markedly influences the therapeutic response of malignant tumors, imaging of the microenvironment is one of the goals researcher have been aiming at for years. Several methods such as positron emission tomography, functional magnetic resonance imaging (MRI) or contrast enhanced MRI/CT are now available. For radiation oncology, tumor oxygenation and perfusion are the most important (patho-) physiological parameters that might be included in radiotherapy regimens and treatment planning. In order to overcome resistance of tumor cells resulting from hypoxia, positron emission tomography (PET) using nitroimidazole tracers is the most advanced technique at this time. Since reproducibility of the PET signal/tracer distribution, thresholding and exact quantification are not thoroughly understood and further investigation is needed before including it into radiotherapy regimens. To image tumor perfusion, dynamic contrast enhanced computed tomography (DCE-CT) or dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) are the most suitable techniques. Co-investigation of tumor oxygenation and perfusion should be performed in order to investigate their interaction and consequences for radiooncology.