Positron emission tomography in lymphoma: Fine tuning of international harmonization project

Lymphoproliferative diseases include a wide range of malignant diseases with various histological characteristics, clinical presentation and therapeutic possibilities. Reliable assessment of the spread of the disease and the knowledge of the biological characteristics of the tumor are the prerequisites of a successful patient treatment. In most patients with lymphoma, positron emission tomography (PET) with fluorodeoxyglucose ( 18 F-FDG) proved to be a useful imaging method which contributes to the assessment of the spread of the disease by identifying increased glycolysis in tumor cells. In the initial phases of the clinical implementation of FDG PET, the method was mostly used to determine the stage of the disease. At present, FDG PET is being increasingly used to assess the effects of therapy and to determine prognostic factor. Today, the treatment of lymphoma patients implies an individualized approach aiming at maximum disease control with the smallest possible risk of late side effects. Numerous prospective studies in patients with lymphoma have contributed to a better understanding of the metabolic changes. FDG PET performed after only 1 or 2 cycles of chemotherapy can assess tumor sensitivity to the therapy. Thus, the long-term response to therapy can be predicted at the very early stage of treatment. Many studies are being conducted in order to assess the potential usefulness of this prognostic information so that the therapy protocols can be altered and the long term administration of drugs that will not result in a sustained response be stopped. It is expected that this approach might result in avoiding late side effects and toxicity. The degree of metabolic activity assessed by interim FDG PET at the very beginning of chemotherapy administration serves as a biomarker of tumor responsiveness to chemotherapy. Because of that, more precise criteria are needed to answer the question “what is a positive interim FDG PET finding”. Our understanding of lymphoproliferative diseases and the effects which some therapeutic procedures have on the metabolism of tissue contribute significantly to the accurate interpretation of FDG-PET/CT findings. For successful utilization of FDG PET/CT, a multidisciplinary team which includes hematology, radiation oncology, diagnostic radiology and nuclear medicine specialists is necessary.