[Comparison of 18F-FDG coincidence SPECT imaging and computed tomography in the initial staging and therapeutic evaluation of lymphomas].

OBJECTIVE: To investigate the clinical value of 18F-fluorodeoxyglucose (18F-FDG) coincidence SPECT imaging versus computed tomography (CT) for malignant lymphoma in the initial staging, early response to therapy, evaluation after completion of therapy and long-term follow-up.

METHODS: 18F-FDG SPECT scans was performed on 61 patients with pathologically proven malignant lymphoma. The mean age of this series was 55 years ranged from 12 to 85 years. The data of these patients were retrospectively analyzed, and the result of 18F-FDG SPECT scan was compared with the CT imaging result performed within 2 weeks before or after FDG scan. 161 18F-FDG SPECT scans were performed for initial tumor staging (n=61), early response to therapy (n=42), evaluation after completion of therapy (n=26) and long-term follow-up (n=32). Each patient had a follow-up >6 months.

RESULTS: (1) Compared with CT scan, 18F-FDG SPECT imaging accurately upstaged the disease for 34.4% (21/61) of these patients at initial staging. It detected the lesions which were undetected by CT including bone marrow infiltration (n=17), foci of lymph node (n=3) and liver involvement (n=1). However, 3 patients were incorrectly staged, either downstaged or upstaged by 18F-FDG SPECT imaging. Of 212 lesions in 61 patients, 18-FDG SPECT imaging detected more lesions than CT (P < 0.01). The correspondence rate of '18-FDG SPECT imaging with marrow histology was 80.3% (49/61). (2) In early evaluation of the response to treatment, the accuracy, positive predictive value and negative predictive value of 18F-FDG SPECT imaging was 85.7%, 92.0% and 76.5% respectively, which is much higher than that of CT (64.3%, 75.0% and 50.0%), therefore, the therapeutic scheme in 21.4% (9/42) of these patients was changed by 18F-FDG SPECT imaging. Of 17 cases with negative 18F-FDG SPECT scan in early evaluation of therapy, clinical remission (13 complete remission and 3 partial remission) were achieved in 16 patients. Of the 25 patients with positive ones, 13 were considered as having progressive disease. (3) In the evaluation at the end of therapy or during follow-up, 58 18F-FDG SPECT imagings were performed in 26 patients. The specificity and positive predictive value were 85.7% and 68.4% versus 59.5% and 43.3%, respectively, by CT scan. Of 14 patients with residual masses detected by CT scan, 8 were diagnosed as complete remission (CR) by 18F-FDG SPECT imaging based on persistently negative FDG scans; The other 6 were interpreted as CR (n=1), partial remission (PR, n=2), non-remission (n=1) and progressive disease (n=2), thus there was only one false-positive FDG scan in these 14 patients.

CONCLUSION: 18F-FDG imaging is quite effective and superior to CT scan for malignant lymphoma in initial staging, evaluation of early response to therapy and after completion of therapy, and long-term follow-up, especially for evaluating the residual masse.