A new method of measuring lean body mass accounts for changes in body composition, enabling improved staging of disease and monitoring of therapy. Fluctuations in lean body mass and body weight in cancer patients can affect the precision of data from molecular imaging when clinicians do not account for these fluctuations. These results were presented at the 2016 Society of Nuclear Medicine and Molecular Imaging Annual Meeting.1
Positron emission tomography (PET) can be used with fluorine-18 fluorodeoxyglucose (F-18 FDG), a radiotracer that mimics the metabolic activity of glucose, to show abnormally high metabolic activity. Abnormally high metabolic activity characterizes tumors, and can be quantified by standardized uptake values (SUVs).
Accurate SUVs of tumors allow assessment of disease progression. An increase in SUVs indicates progression, no significant change indicates stable disease, and a decrease indicates response to therapy.
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SUVs are quantified using patient weight, although F-18 FDG is distributed almost totally in lean body mass rather than adipose tissue. Most methods for the normalization of SUVs only account for overall weight and could incorrectly estimate lean body mass in patients with cancer.
In this study, researchers developed a computed tomography (CT) technique to determine patient-specific lean body mass. This approach to SUV normalization is called SULps.
Analysis of CT scans in 3-month intervals allowed researchers to determine changes in body composition of patients with advanced cancer. Researchers assessed 1080 intervals of CT. Slightly more than 50% of intervals (n = 546) reflected stable lean body mass.
Within the group of intervals with stable lean body mass, 40% of those intervals had decreased adipose tissue, 35% had no change in adipose tissue, and 25% had increased adipose tissue. These changes affect SUV with all calculations except for SULps. SULps accurately reflected metabolic activity with F-18 FDG PET/CT.
“Patients with advanced cancer tend to lose muscle and may gain fat, and these changes in body composition can significantly modify PET results, independent of the actual metabolic activity of the tumor,” said Alexander McEwan, MD, from the University of Alberta, Edmonton, Alberta, Canada, and first author of this study.
“Our study shows that CT-derived SULps is a more robust measurement for patients with advanced cancer undergoing PET imaging. If adopted, this simple change in imaging protocol could lead to significantly more effective care for cancer patients.”
Reference
1. McEwan A, Wieler M, Baracos V, Riauka T. The utility of CT-derived lean body mass correction of weight-based standardized uptake values. 2016 Society of Nuclear Medicine and Molecular Imaging Annual Meeting; June 11-15, 2016; San Diego, California. Scientific paper 1897.
