Utility of FDG-PET and Comparison of FDG-PET and Ga-67 Scintigraphy in Evaluation of B-Cell Indolent Lymphoma.

18Fluoro-2-deoxyglucose positron emission tomography (FDG-PET) has emerged as an important tool for the management of lymphoma patients, but little information has been reported about its usefulness in indolent lymphoma. The aim of this study was to retrospectively assess the usefulness of FDG-PET, and to compare the sensitivity of FDG-PET with gallium 67 citrated scintigraphy (Ga-67), in identifying disease involvement in patients with indolent lymphoma. We also investigated the relationship between FDG-PET and pathologic diagnosis according to the World Health Organization (WHO) classification system.

A total of 118 cases contemporaneously underwent FDG-PET and CT and/or MRI prior to treatment. The histological diagnoses included follicular lymphoma (FL; n=43), MALT-lymphoma (n=52), splenic marginal zone lymphoma (SMZL; n=10), small lymphocytic lymphoma (SLL; n=5) and mantle cell lymphoma (MCL; n=8). In 88 of these 118 cases, Ga-67 was also performed. The involved disease sites were divided into lymph node regions and extranodal regions. The former group was further divided into four lymph node regions:

1. head and neck,

2. chest,

3. abdomen and

4. pelvis.

Among the 118 patients, 401 disease sites were included in the analysis. FDG-PET identified disease sites in 171/189 (90%) FLs, 107/126 (86%) MALTs, 7/16 (44%) SMZLs, 10/19 (53%) SLLs and 51/51 (100%) MCLs. In addition, FDG-PET detected more involvement sites than Ga-67 for all disease sites, except for one region each in the MALTs and SMZLs, namely the eyelid and spleen. Ga-67 was able to detect disease sites assessed by FDG-PET in 48/127 (38%) FLs, 44/78 (56%) MALTs, 3/5 (60%) SMZLs, 1/2 (50%) SLLs and 8/27 (30%) MCLs. There were no anatomical differences in the not-detected disease sites between FDG-PET and Ga-67.

In imaging lymphomas before therapy, FDG-PET was informative for FL, MALT, and MCL, but less reliable for SMZL and SLL. Ga-67 was not suitable for indolent lymphoma, in particular FL and MCL. Given the high sensitivity of FDG-PET, this modality is highly recommended for indolent lymphoma. However, for SMZL and SLL, different anatomical imaging modalities such as CT and MRI should be used.