Emerging role of FDG-PET/CT for global assessment of bone marrow involvement in chronic lymphocytic leukemia

Objectives: Chronic lymphocytic leukemia (CLL) is the most common adult leukemia in the United States. The CLL cells mostly proliferate in the secondary lymphoid tissues, but can also undergo mitosis in the proliferation centers in the bone marrow, which are named “pseudofollicles” areas. PET imaging has been used to detect Richter syndrome, a disease which involves the transformation of CLL to a more aggressive lymphoma. This application relies on measurement of tracer uptake in focal lesions. However, the global assessment of bone marrow involvement has yet to be investigated. This study evaluates a global quantification method to assess bone marrow involvement using FDG-PET/CT based on CT segmentation in CLL patients.

Methods: Eighteen patients with CLL (15 Males, 3 Females, aged 41-80 years) were enrolled in a retrospective study. PET/CT scans were performed 60 minutes after intravenous injection of ¹⁸F-fluorodeoxyglucose (FDG) at the Hospital of the University of Pennsylvania. The patients were matched to 17 healthy controls by sex and age (± 5 year) from the CAMONA study. An iterative thresholding algorithm (OsiriX, Pixmeo SARL, Bernex, Switzerland) was applied to quantify FDG uptake limited to the skeleton, with lower and upper boundaries set at 150-1500 Hounsfield units on the fused PET/CT scans. The global mean standardized uptake value (global SUVmean) was reported for each patient and control subject,. FDG uptake was compared between healthy controls and CLL patients. Statistical analysis was performed using SPSS 24. Results: The average (± SD) of the global bone SUVmean in CLL patients was significantly higher than in healthy control subjects: 1.09 ± 0.13 vs. 0.82 ± 0.21, p = 0.014. Conclusion: The results of this study show that global SUVmean can be used as an indicator for bone marrow metabolic activity in patients with CLL. The increased bone marrow activity may reflect an increased proliferation of CLL cells. Further studies are needed to investigate the correlation of global SUVmean with disease burden and response to treatment.