Characterization of myeloma bone lesions - before and during anti-tumor therapy - using ^sup 18^F-FDG- and ^sup 18^F-fluoride PET/CT

Objectives: The objective of this study is the assessment of the tumor activity and mineralization status using [18F]FDG PET/CT and [18F]Fluoride PET/CTin newly detected multiple myeloma (MM) bone lesions before and after anti-tumor treatment. Methods: In this prospective study, 8 patients with histologically verified MM were included (4 women, 4 men; mean age=62 years; age range=43-78 years). [18F]FDG PET/CT and [18F]Fluoride PET/CT was performed both at baseline and after treatment. All patients showed positive scans. Volumes-of-interest (VOIs) were drawn over all [18F]FDG PET/CT positive bone lesions as well as the corresponding regions in [18F]Fluoride PET/CT. For characterization of bone lesions semi-quantitative parameters (SUVmean, SUVmax) were measured. Textural parameters (Histogram, Heterogenity, higher order calculations) were calculated and were correlated with SUVmax. Results: [18F]FDG PET/CT in 8 patients found 44 metabolically active lesions that were correlated with the corresponding lesions in [18F]Fluoride PET/CT. Overall the lesions showed a response to therapy with a median SUVmax decrease of 46,1% in [18F]FDG PET/CT and a median SUVmax decrease of 49% in [18F]Fluoride PET/CT. Using Spearman correlation SUVmax showed significant correlation between [18F]FDG and [18F]Fluoride scans (p=0,009) in the baseline scan as well as in the post-therapy scan (p=0,003) thus showing no difference in the therapy response between [18F]FDG and [18F]Fluoride scans. None of the calculated textural parameters showed significant correlation with SUVmax either in baseline [18F]FDG or [18F]Fluoride scans. Conclusion: Based on our data, anti-tumor therapy in MM causes not only a decrease in tumor activity but also a decrease in the mineralization status of bone lesions.