Non-Hodgkin's lymphoma (NHL) is categorized according to the cell of origin and clinically indolent or aggressive behavior. 90% are of B cell origin and 10% are of T cell origin. Multifocal, hematogenously disseminated disease with abdominal lymph node and bone marrow involvement is common. Systemic symptoms, fever and weight loss, are seen in less than 20% and are associated with more aggressive subtypes.
In Hodgkin's disease (HD) the cell of origin is unclear. The presence of Reed-Sternberg cells is required for diagnosis. Four histologic subtypes, nodular sclerosing (most common), lymphocyte predominant, mixed cellularity and lymphocyte depleted are recognized. Localized nodal disease characterized by contiguous spread to lymphoid tissues is common. Mediastinal lymph node involvement and systemic symptoms are also common.
Lymphoma is one of the most curable forms of cancer. Approximately 80% of Hodgkin's and 35% non-Hodgkin's lymphoma are curable. Treatment and prognosis depends on histologic subtype / grade and stage.
Essential components of the staging evaluation are physical and laboratory evaluation, chest radiography, computed tomography and bone marrow biopsy. Computed tomography is the conventional imaging modality to determine the extent of disease. Pathologic lymphadenopathy is determined by size criteria.
FDG uptake is seen in Hodgkin's and in non-Hodgkin's lymphoma. Tracer uptake declines with therapy. Areas in which the utility of FDG PET imaging is being evaluated include the initial staging of disease, treatment monitoring, and detection of recurrence (2).
In the few studies to date that have compared CT and FDG PET staging of lymphoma, the sensitivities of the two modalities have been comparable. However, FDG-PET appears superior in treatment monitoring, particularly in distinguishing between residual viable tumor and fibrosis (3). Identification of patients with viable tumor post-treatment allows early intensification of treatment (salvage chemotherapy or bone marrow transplantation) in order to induce complete remission.
Hoh et al (4) compared whole body FDG PET and conventional staging in 7 patients with Hodgkin's disease and 11 patients with NHL. Acknowledging the limitations of a small patient population, the accuracy of PET was comparable to conventional staging. 17/18 patients were accurately staged with FDG PET compared with 15/18 with conventional methods as determined by follow up and biopsy.
In a recent study, Jerusalem et al (5) compared FDG PET to CT in the post-treatment evaluation of 54 patients with Hodgkin's disease or intermediate/high grade non-Hodgkin's lymphoma. Residual masses were seen in 24 subjects on post-treatment CT. Six patients (5/24 with a residual mass on CT and 1/30 without a residual post-treatment mass) had a positive post-treatment FDG-PET study. Disease relapse was seen in all six patients with a positive FDG-PET study, 5/19 patients (26%) with residual masses on CT but negative FDG-PET and 3/29 patients (10%) with both a negative CT and FDG-PET. Evidence of active tumor on FDG-PET post-treatment was shown to have a higher predictive value for relapse than the presence of a residual mass on CT imaging with a positive predictive value of 100% versus 42%.
FDG in studies to date appears to be more sensitive than gallium in detecting viable tumor as illustrated in the index case (7). Pre-treatment scans required in all patients to determine if the tumor is gallium avid may not be necessary with FDG PET.
Positron tomography has inherently greater sensitivity and resolution than conventional gamma camera SPECT, allowing more accurate lesion detection. Less patient preparation and time are necessary for FDG PET than for gallium scans. With PET imaging the patient is required to fast for 6 hours before administration of tracer and is imaged at approximately one hour after injection. In gallium scanning tracer administration and patient imaging are separated by several days in order to allow background clearance of tracer.
2 Maisey, M. M., Wahl, R. L., Barrington S. F., (1999). Atlas of clinical positron emission tomography. (Pp. 51-74). London: Arnold.
3 Delbeke, K. Oncological applications of FDG PET Imaging: brain tumors, colorectal cancer, lymphoma and melanoma. J Nucl Med 1999; 40:591-603.
4 Hoh CK, Glaspy J, Rosen P, Dahlbom M, Lee S J, Kunkel L, Hawkin R A, Maddahi J, Phelps M E. Whole-body FDG-PET imaging for staging of Hodgkin's disease and lymphoma. J. Nucl Med 1997;38(3):343-8.
5 Jerusalem G, Beguin Y, Fassotte, M F, Najjar F, Paulus P, Rigo P, Fillet G. Whole -body positron emission tomography using 18F-fluorodeoxyglucose for posttreatment evaluation in Hodgkin's disease and non-Hodgkin's lymphoma has higher diagnostic and prognostic value than classical computed tomography scan imaging. Blood 1999 Jul 15;94(2):429-33.
6 Front D, Israel O. The role of Ga-67 scintigraphy in evaluating the results of therapy of lymphoma patients. Seminars in Nuc Med 1995 Jan;25:60-71.
7 Paul, R. Comparison of Fluorine-18-2-fluorodeoxyglucose and gallium-67 citrate imaging for detection of lymphoma. J Nucl Med 28: 288-292, 1987.
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