Imaging Cell Proliferation With FLT PET: A Pilot Study in Paediatric Lymphoma Patients With Equivocal FDG PET Findings

Background: Residual masses on follow-up surveillance imaging are frequently detected in paediatric patients with Hodgkin's lymphoma and non-Hodgkin's lymphoma. The residual mass may consist of inflammatory, fibrous or necrotic tissue, or it could represent residual tumor. In most cases, positron emission tomography (PET) with 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (FDG) is useful for distinguishing tumor from fibrosis. However, FDG is not tumor-specific, and increased accumulation of the tracer may be seen in a variety of benign entities which can give rise to false-positive or equivocal FDG PET findings. Alternatively, the uptake of 3'-deoxy-3'-[fluorine-18]-fluorothymidine (FLT) reflects cellular proliferation, and may prove to be a reliable method in resolving equivocal FDG PET findings. Indeed, several studies have demonstrated that FLT can be safely administered to children, and in some cases be more useful than FDG PET in differentiating between infection or inflammation and malignancy. This study hypothesizes that FLT PET can be used as an adjunct imaging modality in paediatric lymphoma patients with equivocal interim or post-therapy FDG PET findings, and that this technique can provide additional diagnostic information which will be useful in distinguishing fibrotic or necrotic residual mass lesions from those that may be harbouring malignancy.