18F-FDG uptake changes in liver and mediastinum during chemotherapy in patients with diffuse large B-cell lymphoma.

PURPOSE: The main objective of this study was to assess the intrasubject and intersubjects variability of 18F-FDG uptake in liver (LIV) and mediastinum (MBP) among patients with diffuse large B-cell lymphoma (DLBCL), treated with different chemotherapy regimens.

PATIENTS AND METHODS: Fifty patients with DLBCL who underwent 18F-FDG PET/CT scan at baseline, after a few cycles of therapy (interim PET) and on completion of therapy (final PET), were enrolled retrospectively. SUVmean and SUVmax values for LIV and MBP, their differences (LIV - MBP SUVmean and LIV - MBP SUVmax), and their changes were calculated, respectively.

RESULTS: Liver uptake significantly increased in the interim in comparison with baseline and final PET, respectively, whereas MBP activity remained stable during chemotherapy. The intersubject variability of 18F-FDG uptake in LIV and MBP ranged from 20.2% to 25.4%.

CONCLUSIONS: The variability of the LIV uptake during chemotherapy should be taken into account when this parameter is used to score the interim PET scan and to make decisions in defining response-adapted therapeutic strategies. Vice versa, the stability of MBP activity during therapy provides a more reliable benchmark for the response assessment.Finally, the intersubjects variability of both parameters should be considered when the visual evaluation of the interim PET is performed by point score models.