Monte Carlo efficiency calibration of a neutron generator-based total-body irradiator |
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Authors: | Roman J Shypailo K J Ellis |
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Institution: | (1) USDA/ARS Children’s Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, 1100 Bates Street, Houston, TX 77030, USA |
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Abstract: | Many body composition measurement systems are calibrated against a single-sized reference phantom. Prompt-gamma neutron activation
(PGNA) provides the only direct measure of total body nitrogen (TBN), an index of the body’s lean tissue mass. In PGNA systems,
body size influences neutron flux attenuation, induced gamma signal distribution, and counting efficiency. Thus, calibration
based on a single-sized phantom could result in inaccurate TBN values. We used Monte Carlo simulations (MCNP-5; Los Alamos
National Laboratory) in order to map a system’s response to the range of body weights (65–160 kg) and body fat distributions
(25–60%) in obese humans. Calibration curves were constructed to derive body-size correction factors relative to a standard
reference phantom, providing customized adjustments to account for differences in body habitus of obese adults. The use of
MCNP-generated calibration curves should allow for a better estimate of the true changes in lean tissue mass that many occur
during intervention programs focused only on weight loss. |
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