FDG PET in the evaluation of treatment for lymphoma: clinical usefulness and pitfalls.

Positron emission tomography (PET) with 2-[fluorine-18] fluoro-2-deoxy-d-glucose (FDG) may play an important role in the evaluation and management of malignant lymphoma. FDG uptake is predictive of therapeutic response during the course of treatment. After completion of chemotherapy, residual abnormalities representing either residual tumor or necrotic or fibrotic tissue are not uncommon, and FDG PET may be more accurate than computed tomography (CT) or magnetic resonance imaging in assessing residual disease and identifying patients who require more intense treatment. However, posttreatment FDG PET does not help exclude the presence of minimal residual disease, which may lead to disease relapse. Furthermore, FDG is not a tumor-specific substance, and increased accumulation may be seen in a variety of benign entities and scenarios (eg, infection, drug toxicity, granulocyte colony-stimulating factor therapy, radiation therapy, physiologic activity, postoperative or postbiopsy changes, fracture, degenerative change, injection leakage), which may yield false-positive findings. Nevertheless, recognition of these entities and correlation of FDG PET findings with clinical and other radiologic findings-especially those at combined PET and CT or PET-CT fusion imaging-allows improved diagnostic accuracy. If the interpretation of positive findings is exceptionally difficult, short-term follow-up may be helpful. (c) RSNA, 2005.