THE ROLE OF FDG - PET IMAGING IN LYMPHOMA TAALAB, K.M.(1), SALEH, A.(1), NASHED, A.(1), IMAN, W.(1) AND MOUSTAFA, H.(2) Nuclear Medicine Department, International Medical Center (IMC) and Cairo University, Egypt.

Positron Emission Tomography (PET) imaging using (F-18) fluorodeoxy glucose (FDG), has been introduced for the first time in Egypt in October 2004, and since that time, this technique has created a new trend in the diagnosis and management of the lymphomas, providing unique metabolic information. FDG uptake in lymphoma is a function of increased anaerobic metabolism as well as longer residence time of FDG in malignant cells relative to most normal tissues. Over several decades computed tomography (CT) has been the principal imaging modality for the staging and restaging of Lymphoma, although it can have shortcomings originating from its sized-based criteria, particularly, in the post-therapy status. Purpose: To evaluate the impact of FDG-PET on management of patients with lymphoma and compare its findings with the conventional investigational methods, mainly the contrast enhanced CT and to evaluate the common causes of discrepant findings between the two modalities.
Patients and Methods: A group of 460 consecutive patients with diagnosis of lymphoma (Males: 228, Females: 172, Age range:6-73 years, median age:29 years), were included. They comprised 118 newly diagnosed cases, 182 cases for therapy monitoring and 160 cases with suspicious relapsed disease. The group consisted of a mixture of NHL (n=311 patients) and HL (n=149).
All patients underwent FDG PET and contrast enhanced CT within a maximum of 4 weeks time window.
A final diagnosis was established at 1850 sites for comparison between PET and CT.
Concordant PET and CT findings were regarded as positive or negative for disease. Discordant findings were defined as positive for disease, if it was confirmed by the histological examination, by the clinical progressive course or by the follow up CT.s.
Results: Accuracy, Positive Predictive Value and Negative Predictive Values of FDG-PET and contrast enhanced CT were 95.8%, 96.4% and 91.1% vs. 85%, 85% and 55% respectively. Agreement of both methods was excellent (k = 0.89). A difference with p<0.05 was considered significant regarding the exclusion of disease with FDG PET, compared with contrast enhanced CT.
Conclusion: FDG PET is more accurate than the conventional investigational methods; including contrast enhanced CT in evaluation of Lymphoma and can yield findings that lead to change in treatment strategy.