Study of the Counting Efficiency of a WBC Setup by Using a Computational 3D Human Body Library in Sitting Position Based on Polygonal Mesh Surfaces

Abstract

A realistic computational 3D human body library, called MaMP and FeMP (Male and Female Mesh Phantoms), based on polygonal mesh surface geometry, has been created to be used for numerical calibration of the whole body counter (WBC) system of the nuclear power plant (NPP) in Doel, Belgium. The main objective was to create flexible computational models varying in gender, body height, and mass for studying the morphology-induced variation of the detector counting efficiency (CE) and reducing the measurement uncertainties. First, the counting room and an HPGe detector were modeled using MCNPX (Monte Carlo radiation transport code). The validation of the model was carried out for different sample-detector geometries with point sources and a physical phantom. Second, CE values were calculated for a total of 36 different mesh phantoms in a seated position using the validated Monte Carlo model. This paper reports on the validation process of the in vivo whole body system and the CE calculated for different body heights and weights. The results reveal that the CE is strongly dependent on the individual body shape, size, and gender and may vary by a factor of 1.5 to 3 depending on the morphology aspects of the individual to be measured.

MaMP and FeMP: computational mesh phantoms applied for studying the variation of WBC efficiency using a NaI(Tl) detector

“…The CE results obtained for the MaMP and FeMP of 1.80 m in height and 81 kg and 83 kg in weight for the male and female phantoms, respectively shown that the CE values for MaMP are systematically smaller than those for FeMP over the whole energy range, with differences of the order of 5-7%, and this was observed also for female and male phantoms of different heights. The same results were observed in our previous work using the HPGe detector, when comparing the MaMP and FeMP phantoms with 1.80 m in height and ∼85 kg [8]. This is due to the anatomical characteristics of the two phantoms.…”

“…This trend result is not systematic for all FeMP phantoms of different heights and approximate same weights. A different trend was found in a previous study [8] while simulating the CE for a HPGe detector and FeMP phantoms of ∼80 kg and ∼100 kg in a different counting geometry.…”

“…In a previous study [8], the HPGe detector and the MaMP and FeMP phantoms of different heights and weights of ∼80 kg and ∼100 kg sitting on chair were simulated and the results showed that CE increases as the body height increases. In the geometry used with the HPGe detector, the detector is fixed at an angle of 24° on the wall in front of a sitting chair, while in the other set-up the phantom is lying on a reclining chair and the detector is hanging vertically, pointing to the reference point of the phantom.…”

“…Thus, some anatomical parameters were used to find a possible trend curve which could explain the CE simulation results found for different human body shapes and sizes and for this specific counting geometry. In a previous study [8] the CE, as a function of BBI, was calculated for different phantom sizes and genders. A linear correlation was revealed for 121.80 keV to 778.90 keV gammaray energies, but this linearity was not systematic for all data sets the 3D human body library developed.…”

“…Computational 3D human body simulations using Monte Carlo codes represent a less expensive noninvasive technology, which has been applied for in vivo measurement calibration over several years [5][6][7]. In our previous work a 3D human body library called MaMP and FeMP (Male and Female Mesh Phantoms), which spans variations in height, weight and gender, was developed and successfully applied to a whole body calibration using a HPGe detector [8]. Here we report the extension of this study to the investigation of the influence of body size, shape and gender on the detector efficiency of a NaI(Tl) detector counting system.…”