Computed Tomography–Based Lean Body Mass Calculations May Improve Accuracy of PET for Patients With Cancer


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Patients with cancer often experience significant fluctuations in weight and lean body mass. Neglecting to account for these changes can prevent clinicians from obtaining precise data from molecular imaging, but a new method of measuring lean body mass takes changes in individual body composition into account for better staging of disease and therapeutic monitoring, said researchers at the 2016 Annual Meeting of the Society of Nuclear Medicine and Molecular Imaging (SNMMI).1

Improving the Accuracy of PET Imaging

  • Researchers analyzed CT scans in 3-month intervals to gauge changes in body composition of patients with advanced cancer.
  • A total of 1,080 intervals of CT were evaluated, and just over 50%, or 546 intervals, reflected stable lean body mass. Of this smaller group with stable lean body mass, 40% experienced a decrease in adipose tissue, 35% showed no change in adipose tissue, and 25% showed an increase in adipose tissue.
  • These changes affect standardized uptake values using all calculations except SULps, which accurately reflected metabolic activity via FDG–PET/CT.

Positron-emission tomography (PET) has become a standard of care in the management of many patients with cancer. The radiotracer fluorine-18 fluorodeoxyglucose (FDG), which closely resembles the metabolic activity of glucose in cells throughout the body, emits a signal that is detected by the PET scanner. Image reconstructions of these signals indicate where there are areas of abnormally increased metabolic activity, quantified by standardized uptake values. Accurate tumor standardized uptake values enable clinicians to assess disease progression, reflected by an increased value; stable disease, reflected by no significant changes in standardized uptake value; and successful response to therapy, reflected by a decrease in standardized uptake value.

Radiotracer tumor standardized uptake values are quantitatively measured using patient weight. However, FDG is distributed almost exclusively in lean body mass, not fatty tissue. Current methods of standardized uptake value normalization tend to focus on overall weight and may significantly over- or underestimate lean body mass in patients with cancer.

Study Details

For this study, researchers developed a computed tomography (CT) technique to determine patient-specific lean body mass. This method of standardized uptake value normalization, using patient-specific lean body mass, is termed SULps.


Our study shows that CT-derived SULps [standardized uptake value normalization, using patient-specific lean body mass] is a more robust measurement for patients with advanced cancer undergoing PET imaging.
— Alexander McEwan, MD

“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 principal study author Alexander McEwan, MD, Professor and Chair of the Department of Oncology at the University of Alberta. “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.”

More Precise PET Measurements

Researchers analyzed CT scans in 3-month intervals to gauge changes in body composition of patients with advanced cancer. A total of 1,080 intervals of CT were evaluated, and just over 50%, or 546 intervals, reflected stable lean body mass. Of this smaller group with stable lean body mass, 40% experienced a decrease in adipose tissue, 35% showed no change in adipose tissue, and 25% showed an increase in adipose tissue. These changes affect standardized uptake values using all calculations except SULps, which accurately reflected metabolic activity via FDG–PET/CT.

More precise PET measurements made with the use of CT data could increase the accuracy of PET imaging interpretation in groundbreaking clinical trials for new cancer therapies and for more personalized medicine in the clinic. ■

Disclosure: Dr. McEwan reported no potential conflicts of interest.

Reference

1. McEwan A, Riauka TA, Wieler M, et al: 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. Abstract 1897.


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