The Utility of 18F-FDG PET for Malignant Lymphoma; Single Cancer Center Survey.
Authors: Tamai Yotaro , Imataki Osamu , Kawakami Kimihiro , Tanaka Terukazu 
Published: October 2019

Purpose It is widely known that positron emission tomography (PET) with 18F-fluorodeoxyglucose (FDG) is useful for the staging of disease and prediction of clinical prognosis for malignant lymphoma patients. Although the sensitivity of evaluation by positron emission tomography with fluorodeoxyglucose is higher than conventional computed tomography (CT) scanning in detecting lymphoma lesions, inevitably false positive occurred in some subtype of lymphoma and specificity would decrease in FDG PET evaluation. We assessed how the sensitivity and specificity increase in the combined use of FDG PET and CT in the clinical evaluation of malignant lymphoma of single cancer center survey and ability to evaluate bone marrow involvement of lymphoma cells by FDG PET.

Methods We retrospectively reviewed consecutive patients diagnosed as malignant lymphoma in our hospital between October 2002 and March 2006. Diagnosis was confirmed histologicaly and non malignant disease was excluded. We abstracted 33 cases of staging and 62 cases of efficacy evaluation after treatment, those received FDG PET and CT concomitantly or within 1 month. We calculated the sensitivity and specificity in each modality and combined modality according to standard reference, which was defined by the pathology and clinical course followed more than 3 months. Radiological diagnosis was referred by more than 1 radiologist and findings were reviewed by 1 hematologist. Accuracy of a diagnostic modality was evaluated by using receiver operating characteristic (ROC) analysis.

Results Subtype of lymphoma in 95 patients contained 21 cases of Hodgkin lymphoma, 28 of low grade lymphoma, 37 of high grade lymphoma and 9 of T cell lymphoma. Accordance of initial staging (Ann Arbor classification) by CT with FDG PET was 75.8% (25/33) and 8 discordance cases included 5 up-staged cases and 3 down-staged cases. In other hand, accordance of re-staging after chemotherapy was 74.2% (46/62) and 16 discordance cases included 5 up-staged cases and 11 down-staged cases (5 Hodgkin and 3 low grade lymphomas). Sensitivity and specificity in initial staging were 87% and 100% in CT evaluation and 87% and 100% in FDG PET, respectively. Sensitivity and specificity in re-staging were 81% and 78% in CT evaluation and 78% and 98% in FDG-PET, respectively. In all among 7 patients diagnosed as bone marrow infiltration of lymphoma cells by FDG PET, no histological confirmation of involvement was obtained.

Conclusion Diagnostic accuracy of FDG PET was as same as CT in initial staging. While mentioned to the diagnostic performances of FDG PET in re-staging, CT showed relatively low specificity and FDG PET showed low sensitivity, respectively, however diagnostic accuracy of both modalities was exploit evaluated as same value. Diagnosis of bone marrow involvement by FDG PET was not reliable. Taken together, these results suggested that selected patients were examined and selected radiologists reviewed images with highly biased viewpoints that resulted in over diagnosis. This circumstance was characterized in cancer center, and in which CT imaging might exert enough diagnostic value compared to FDG PET in initial diagnosis.