Defining the Role of FDG PET in Head and Neck Cancer.
The purpose of this article is to elucidate the role of 2-[18F] Fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) in evaluating patients with head and neck cancer. This will include background information on patient preparation and image acquisition. Normal patterns of uptake will be described in reference to computerized tomography (CT)/magnetic resonance imaging (MRI) to illustrate the relationship of physiology to the anatomic landmarks. Common clinical scenarios will be discussed, including staging, identifying recurrence, monitoring therapy, and secondary cancers.The fundamental basis of this imaging modality is the altered metabolism of tumor tissue, which includes an increase in glycolysis. FDG is a glucose analog, which is essentially trapped within tumor cells with increased glycolysis, and allows these malignant cells to be localized. Conventional methods, such as CT and MRI, are dependent on distortion of the normal anatomy in identifying the presence or absence of tumor. CT scanning for example is essentially dependent on nodal enlargement criteria for localizing lymph node metastasis and is less specific in identifying tumor in normal sized lymph nodes or in enlarged nodes not involved by tumor. Following surgery, radiation, and/or chemotherapy, the normal anatomy is distorted and these conventional methods become less specific in distinguishing recurrence from post treatment changes. FDG PET can provide more accurate information in identifying tumor before and after treatment. This improvement in specificity augments our current ability to stage the extent of disease at presentation and monitor response to therapy.(1) However, the anatomic resolution of these conventional methods are superior to FDG PET, and this advantage should be used to accurately localize both the normal and abnormal findings on FDG PET.