18-FDG-PET for the assessment of residual masses on CT following treatmentof lymphomas

Background: The problem of residual masses on post-treatment CT scans is a continuing dilemma for the oncologist treating malignant lymphomas. These m asses may contain active disease or represent only necrotic tumour which co ntinues to shrink without further treatment or post-treatment fibrosis whic h remains stable on continued follow-up. 18-FDG-PET offers a novel metaboli c imaging modality, which can differentiate malignant from benign tissue on the basis of increased glycolytic activity. Patients and methods: Thirty-two patients (15 with Hodgkin's disease (HD) a nd 17 with aggressive histology non-Hodgkin's lymphoma (NHL)) who had resid ual masses on their posttreatment CT scans underwent 18-FDG-PET. The post-t reatment CT and PET scans were compared and the accuracy of the 18-FDG-PET in assessing residual masses was evaluated using clinical and pathological follow-up data. Results: Nine patients had positive post-treatment 18-FDG-PET, eight (89%) of whom have relapsed. Twenty-three patients had negative post-treatment PE T with only two relapses in this group. The 2 patients who relapsed had agg ressive NHL while none of the 11 HD patients with negative PET relapsed. Th e median follow-up of patients in continued complete remission is 38 months . Conclusions: 18-FDG-PET can differentiate between residual masses containin g viable lymphoma where further treatment will be required to achieve cure and those representing ablated disease, where unnecessary treatment and add itional morbidity may be avoided.