Calibration of a prompt gamma in vivo neutron activation facility for direct measurement of total body protein in intensive care patients

The Auckland in vivo prompt gamma neutron activation analysis facility has been calibrated for direct measurement of protein and chlorine in intensive care patients without reliance on hydrogen as an internal standard. These patients often present with massive fluid overload and the technique using hydrogen as an internal standard may be invalidated. Eight variable anthropomorphic phantoms containing physiological amounts of the major body elements were constructed from commercially available flexible polythene tubes and used for calibration. These phantoms are easily disassembled and reassembled to a different size and shape. Accuracy and precision for protein and chlorine were assessed by repeated scanning of a 64 kg anthropomorphic minced-meat phantom followed by chemical analysis of the meat. Reproducibilities for protein and chlorine were 2.9% and 10.6%, respectively, for a mean dose equivalent to a subject of approximately 0.15 mSv. Chemical analysis for protein and chlorine did not differ significantly from the scanning results.