ARS | Publication request: Monte carlo efficiency calibration of a neutron generator-based total-body irradiator

Submitted to: American Nuclear Society
Publication Type: Abstract Only
Publication Acceptance Date: January 1, 2009
Publication Date: April 5, 2009
Citation: Shypailo, R.J., Ellis, K.J. 2009. Monte carlo efficiency calibration of a neutron generator-based total-body irradiator [abstract]. American Nuclear Society. Log: 134.

Technical Abstract: The increasing prevalence of obesity world-wide has focused attention on the need for accurate body composition assessments, especially of large subjects. However, many body composition measurement systems are calibrated against a single-sized phantom, often based on the standard Reference Man model [ICRP-23]. Prompt-gamma neutron activation (PGNA) provides the only direct measure of total body nitrogen (TBN), an index of the body’s lean tissue mass. The performance of PGNA analysis systems is affected by body habitus – differences in body size will influence neutron flux attenuation, induced gamma signal distribution, and counting efficiency. Thus calibration based on a single phantom could result in inaccurate TBN values. We have used Monte Carlo stimulations (MCNP-5; Los Alamos National Laboratory) in order to more efficiently investigate system response to the range of body weights (100-250 kg) and body fat distributions (25%-65%) in obese humans. MCNP codes were constructed to map the system’s response to a range of body proportions. Calibration curves were then constructed to derive body-size correction factors relative to a reference anthropomorphic phantom. These correction factors provide, for the first time, the customized adjustments needed to account for differences in body weight and size of obese adults. MCNP stimulations allowed for the evaluation of a greater range of body dimensions than would be practical via standard phantom construction and measurement. Additonally, the use of MCNP-generated calibration curves will allow for a better estimate of the true changes in lean tissue mass during intervention programs focused only on weight loss.