Role of FDG-PET/CT Staging in FL
FL staging is based primarily on the Cotswold modified Ann Arbor staging system,which categorizes stage based on the number and location of nodal groups involved.3 The FL International Prognostic Index (FLIPI) is additionally used for risk stratification, and also includes the number of nodal groups involved. Therefore, accurate determination of nodal and extranodal disease is important for classifying disease stage and stratifying risk.
Historically,staging was conducted by CT. More recently, whole-body 18F-FDG PET/CT has emerged as a more accurate method for FL staging, particularly for early-stage disease.3 It was demonstrated to have a sensitivity and specificity of 98% and 94%, respectively, with a positive predictive value of 95% and a negative predictive value of 98%, which was significantly more accurate than conventional radiologic studies (P =.023).4 Furthermore, several studies have shown that 18F-FDGPET/CT upstages or down stages approximately 24% of patients with FL.3 This effect is even greater for patients with suspected early-stage disease — approximately 31% to 62% of patients thought to have stage I or stage II disease were upstaged to stage III or stage IV disease by 18F-FDG PET/CT.
The support for the use of 18F-FDG PET/CTfor FL staging is increasing, and now the NCCN recommends either whole-body 18F-FDG PET/CT or chest/abdominal/pelvic CT with contrast as part of a standard FL workup.2 An expert consensus of the International Conference on Malignant Lymphoma Imaging Working Group recommends 18F-FDG PET/CT staging as the preferred method for all FDG-avid lymphomas, including FL.5
It is thought that this more sensitive imaging modality leads to more accurate staging, thereby resulting in better patient selection for treatment. “PET staging really provides greater confidence in using RT as the primary management because you can be much more confident that the patient is truly only stage I or II as opposed to stage III or IV,” Dr Hoppe said.
Furthermore,18F-FDG PET/CT enables an accurate determination of which nodal sites are involved, thereby aiding in better RT planning. Dr Hoppe said that with a CT scan, lymph node size determines whether it is involved. “With a PET scan,” Dr Hoppe noted, “FDG uptake can show us lymph nodes that are normal in size but that are infected by lymphoma.” He said that this is taken into account when designing radiation fields, to ensure all involved lymph nodes are treated. For example, one study showed that 18F-FDG PET/CT resulted in a change in the radiation field for 14% of patients with early-stage FL.3