Intensity of bone involvement: a quantitative 18F-FDG PET/CT evaluation for monitoring outcome of multiple myeloma

Purpose The parameter intensity of bone involvement (IBI) was recently proposed to quantitatively assess patients with multiple myeloma using F-18-fluorodeoxyglucose-PET combined with computed tomography (F-18-FDG PET/CT) images. Here, we aimed to calculate IBI variation (Delta IBI) between two consecutive PET/CT of the same patient and verified its relationship with a subjective visual analysis of the images and with clinical outcome. Methods Consecutive whole-body F-18-FDG PET/CT performed to assess the outcomes of 29 patients diagnosed with multiple myeloma were retrospectively evaluated. Delta IBI was calculated after bone segmentation, using liver standardized uptake value as a threshold to determine metabolically active volumes in the skeleton. For each pair of consecutive PET/CTs, two nuclear medicine physicians classified visually the most recent image as PET-remission, PET-progression or PET-stable when compared to the previous examination. Results The lowest Delta IBI was -1.27 and the highest was 0.29. PET-remission was related to Delta IBI <0 (median = -0.10; -1.27 to +0.03), while PET-progression was related to Delta IBI >0 (median = 0.02; -0.07 to +0.29). Delta IBI around zero was found in images classified as PET-stable (median = 0.00; -0.08 to +0.06). Significant difference in Delta IBI was found between the three groups. Multivariate stepwise analysis showed that IBI value at diagnostic PET/CT, serum calcium and percentage of plasma cells in the bone marrow are independent prognostic factors. Conclusion Delta IBI provides quantitative data for variations of F-18-FDG uptake in the bone marrow during the follow-up of the patients. In addition, higher IBI values at diagnosis are associated with a higher risk of patient's death.