Comparison of London criteria and quantitative analysis in interpretation of interim F-18-FDG PET-CT in high grade non Hodgkin's lymphoma

Objectives London criteria (Meignan et al Leuk Lymphoma.2009)were proposed for standardization of reporting criteria for interim PET/CT in patients with lymphoma. This prospective study was carried to find out the utility of London criteria in interpretation of interim 18F-FDG PET-CT in patients with High grade Non Hodgkins Lymphoma(HG-NHL).

Methods 30patients with diagnosis of HG-NHL (18-DLBCL;8-ALCL;4T-Cell Lymphoma)who underwent F-18-FDG PET-CT at baseline (PET/CT1) and after 4 cycles of chemotherapy (PET/CT4) were included in this study.Interim PET-CT scans were independently interpreted by 2 nuclear medicine physicians according to London criteria and scores were given to the hottest lesion and consensus was reached after discussion.For quantitative analysis ROI was drawn over hottest lesion in each scan using a 40% threshold.

Results After a median period of 375 days,9 patients had an event and 21 did not have any event.Best predictive accuracy was achieved by taking scores of 1,2,3 as negative and scores of 4,5as positive.6 patients had a score of 4 and above whereas 24 had lesser score.During follow up period,5/6 patients with positive PET/CT4 had an event and mean EFS was 198days(range=158-239)whereas only 4/24 patients had an event in PET negative group and mean EFS was 320days(range= 213-511)days.The difference between two groups was statistically significant(p=0.004).Threshold predicting best possible accuracy to predict progression was 78.5% reduction in SUVmax between PET/CT1 and PET/CT4.Both quantitative analysis and qualitative analysis using London criteria had similar sensitivity,specificity,positive predictive value, negative predictive value,accuracy of 56%, 95%,83%,83% and 83% respectively to predict progression.

Conclusions Qualitative analysis using London Criteria appears to perform equally when compared to quantitative analysis in interpreting PET/CT4 to predict EFS in patients with HG-NHL