18-FDG-PET as a prognostic indicator in the treatment of aggressive non-Hodgkin's lymphoma-comparison with CT

Less than 50% of newly diagnosed patients with aggressive histology Non-Hod gkin's Lymphoma (NHL) are cured with standard treatment. The ability to acc urately monitor response to treatment is crucial in order to select out pat ients who need more intensive or salvage treatment. This study assesses the accuracy of FDG-PET as compared to CT in remission assessment following tr eatment of aggressive NHL, and its value in estimating relapse-free surviva l. It also evaluates the prognostic value of early interim PET scan in pred iction of treatment outcome. Forty-nine adult patients with biopsy-proven a ggressive NHL between September 1993 and December 1997 were included. All p atients had pre-treatment FDG-PET demonstrating increased uptake in sites o f disease. Forty-five patients had a post-treatment PET to assess remission status and 4 had an interim but not a post-treatment PET. Thirty-three of these patients also had a pre- and a post-treatment CT scan. Twenty-three o f the 49 patients had an interim PET during chemotherapy to assess early re sponse. PET and CT scan results were correlated with relapse data to examin e their accuracy in remission assessment and prediction of prognosis. The m edian follow-up duration is 30 months. Overall the result of post-treatment PET scan appears to predict disease ou tcome, with relapse rates of 100% (9/9) and 17% (6/36) for positive and neg ative PET respectively (p<0.001). In a subgroup of 33 patients, direct comp arison of post-treatment PET and CT shows that PET was more accurate than C T in assessing remission status following treatment. Relapse rate was 100% for positive PET and only 18% for negative PET (p<0.001), compared to 41% a nd 25% for patients with positive and negative CT respectively (p>0.1). PET was particularly useful in assessment of residual masses seen on CT scan. The interim PET provided valuable information regarding early assessment of response and long-term prognosis, with no relapses in patients with no or minimal residual uptake compared to 87.5% relapse rate in patients with per sistent PET activity (p<0.001). FDG-PET is an accurate method of assessing remission and estimating prognosis following treatment of aggressive NHL, w ith positive and negative predictive accuracies of 100% and 82% respectivel y. PET is more accurate than CT in assessing remission and prediction of re lapse-free survival. An interim PET scan after 2-3 cycles of chemotherapy p redicts the long-term outcome early-on and has a high negative predictive v alue (100%). This may assist to separate at an early stage good-prognosis p atients who are likely to be cured with standard chemotherapy from those pa tients with poorer prognosis who require alternative treatment.