SUVmax cut-off between aggressive and indolent non-Hodgkin lymphoma in non-time of flight FDG PET/CT and time of flight FDG PET/CT

Objectives: Non-Hodgkin lymphoma (NHL) cases with inconclusive biopsy findings are not infrequently referred for FDG PET/CT. Maximum standardized uptake value (SUVmax) more than 10 was suggestive of aggressive nature of NHL in previous studies. Now we are checking whether this cut-off differs in the modern time of flight (TOF) PET/CT and its accuracy in comparison with that in conventional non-TOF PET/CT.

Methods: : Retrospectively, 328 patients were selected by the following inclusion criteria: biopsy-proven NHL with no more than one histopathological type; new cases with less than 90 days between obtaining biopsy and FDG PET/CT scanning; recurrent cases with time interval more than six months since the last therapy with no history of transformation; and blood glucose less than 150mg/dL. Two hundred forty-six (246) selected patients were scanned with non-TOF PET/CT, and 82 patients were scanned with TOF ¹⁸F-FDG PET/CT. Results: New aggressive NHL had significantly higher SUVmax than new indolent NHL in both, non-TOF FDG PET/CT (13.6 ±7.7 vs.5.3±3.4, P<0.0001) and TOF FDG PET/CT (20.5 ± 9.8 vs. 6.6±4.7, P<0.0001).A receiver operating characteristic curve analysis for new cases in non-TOF PET/CT (n=204), demonstrated that SUVmax of 10 as the most balanced cut-off between aggressive and indolent NHL, with the area under the curve (AUC) of 86%, specificity of 94%, and sensitivity of 71%. While 13 was the most balanced cut-off for new cases scanned by TOF PET/CT (n=57) with AUC of 91%, a specificity of 95.5%, and a sensitivity of 77%. Conclusion: SUVmax>10 in non-TOF PET/CT and >13 in TOF PET/CT were highly suggestive of an aggressive nature of NHL, while there was an overlap between indolent and aggressive NHL in the lower SUVmax levels. The accuracy of the SUVmax cut-off was higher in TOF than non-TOF PET/CT; 91% vs. 86%.