Measuring tumor response to treatment based on computed tomography (CT) and/or magnetic resonance imaging (MRI) has been a widely debated issue (response criteria in solid tumors [RECIST] and World Health Organization criteria). Furthermore, early identification of nonresponding patients is of great importance because the rates of response of common malignant solid tumors to chemotherapy are in the range of only 20-30%. Therefore, quantitative imaging of tumor metabolism with 18F-FDG PET/CT may provide important advantages and thus reduce side effects and costs of ineffective therapy. However, the evidence to date for the use of 18F-FDG-PET/CT with this indication is limited.