[18F]-FDG positron imaging in clinical management of lymphoma patients

Abstract [18F]-FDG is a glucose analogue labelled with a short-lived positron emitter. During the past decade, it has been proposed to detect in vivo lymphoma lesions with PET, a new non-invasive imaging modality. We aimed at reviewing the current experience with FDG in several clinical settings of lymphoma. Due to the lack of specificity of FDG for lymphoma, histology remains compulsory to establish the diagnosis. Nevertheless, in the case of AIDS, FDG imaging has been proposed to differentiate lymphoma and opportunistic infections in brain lesions. To explore lymphoma extension, FDG-PET highlights more lesions than CT or the clinical examination and results in upstaging 13% of cases. It could also be used for selecting a site for biopsy when the location considered first clinically is difficult to access. Staging lymphoma with FDG-PET also provides baseline images for subsequent evaluation of therapy, which is one of the most promising indications: a negative scan predicts response to therapy and subsequent remission with a predictive value of 89%, and a positive scan either reflects resistance or predicts relapse with a predictive value of 83%. The current achievement of FDG imaging is the early detection of recurrence or of viable tissue in residual masses that remain several months after treatment. Both its sensitivity (84%) and its specificity (95%) overwhelm the values of conventional imaging, mainly CT and gallium-67 scintigraphy. When PET, as a new clinical imaging modality, is not yet widely demanded by clinicians and/or the number of FDG examinations is less than 500 per year, a ‘hybrid’ gamma-camera or CDET can be an alternative to dedicated PET. For 3 years, we have been using FDG-CDET in the 2D mode without attenuation correction, and obtained the following accuracy in a total of 40 examinations that could be evaluated: 85% for assessment of chemotherapy and 92% to detect recurrences and evaluate residual masses. Our preliminary results also stress the interest in FDG examination in childhood lymphoma, with the same indications as in adults.