Monte Carlo calculations for efficiency calibration of a whole-body monitor using BOMAB phantoms of different sizes

Abstract

Internal contamination due to high-energy photon (HEP) emitters is assessed using a scanning bed whole-body monitor housed in a steel room at the Bhabha Atomic Research Centre (BARC). The monitor consists of a (203 mm diameter × 102 mm thickness) NaI(Tl) detector and is calibrated using a Reference BOMAB phantom representative of an average Indian radiation worker. However, a series of different size physical phantoms are required to account for size variability in workers, which is both expensive and time consuming. Therefore, a theoretical approach based on Monte Carlo techniques has been employed to calibrate the system in scanning geometry with BOMAB phantoms of different sizes characterised by their weight (W) and height (H) for several radionuclides of interest ((131)I, (137)Cs, (60)Co and (40)K). A computer program developed for this purpose generates the detector response and the detection efficiencies (DEs) for the BARC Reference phantom (63 kg/168 cm), ICRP Reference male phantom (70 kg/170 cm) and several of its scaled versions. The results obtained for different size phantoms indicated a decreasing trend of DEs with the increase in W/H values of the phantoms. The computed DEs for uniform distribution of (137)Cs in BOMAB phantom varied from 3.52 × 10(-3) to 2.88 × 10(-3) counts per photon as the W/H values increased from 0.26 to 0.50. The theoretical results obtained for the BARC Reference phantom have been verified with experimental measurements. The Monte Carlo results from this study will be useful for in vivo assessment of HEP emitters in radiation workers of different physiques.

Longitudinal monitoring of whole body counter NaI(Tl) detector efficiency

“…Modeling individual detectors and instituting regular efficiency evaluations provides an opportunity for tracking the performance of system components more thoroughly than overall system QC testing. The fairly large number of NaI(Tl) detectors in our WBC may necessitate this type of detailed testing, as many other WBC systems make use of fewer detectors (Krstic and Nikezic 2012, Paiva et al 2016, Bhati et al 2012. It may be easier to isolate and identify problems within these simpler systems, but it seems reasonable to assume that more detailed performance evaluations would benefit them as well.…”

“…Perhaps the most common approach to system calibration involves the use of Monte Carlo particle transport modeling coupled with phantom standards containing known amounts of radioisotopes. One can easily find many articles in the literature outlining such calibration efforts leading to improved precision and accuracy (Shypailo and Ellis 2011, Bhati et al 2012, Krstic and Nikezic 2012. Normally, the work presented involves initial system calibration, or recalibration on the heels of system reconfiguration; yet, there is very little in the literature focusing on longitudinal assessment of detector performance.…”

Estimation of protein requirements in Indian pregnant women using a whole-body potassium counter

“…The phantoms were also used to account for the different detector efficiencies associated with varying body geometries. Monte-Carlo calculations were then applied to the different geometries to simulate the phantoms and human bodies of different shapes and sizes (22–24). The accuracy error of the WBKC was 2.8%.…”

Monte Carlo simulation of a whole-body counter using IGOR phantoms

“…Various MC computer codes have been used so far: 'FLUktuierende KAskade' (FLUKA) (25) , 'Monte Carlo N-Particle' (MCNP) (26 -33) , 'Electron Gamma Shower' (EGS) (5,6,34,35) , 'PENetration and Energy LOss of Positrons and Electrons' (PENELOPE) (32) , 'GEometry ANd Tracking' (GEANT) (36) or local codes developed ad hoc (37) . MC calculation has been used to compare different mathematical phantoms used in WBCs (10,26,27,29,31,35,38) or to compare the measurements obtained with a physical phantom with the results obtained by a simulated version of this phantom (5,6,30,35,37) . MC calculations are also used to investigate how the counting efficiency of the WCB depends on various parameters of the system that may be sources of uncertainty, such as the difference between the shape and size of the person to be monitored and the phantom, the measuring geometry, notably the position of the detector, the phantomdetector distance, the distribution of the radionuclides in the body, etc.…”

“…MC calculations are also used to investigate how the counting efficiency of the WCB depends on various parameters of the system that may be sources of uncertainty, such as the difference between the shape and size of the person to be monitored and the phantom, the measuring geometry, notably the position of the detector, the phantomdetector distance, the distribution of the radionuclides in the body, etc. (5,29,33,37,39) The objects of the work presented in this paper are as follows: (a) validating a MC simulation used to investigate the response of a WBC with an IGOR phantom, by comparing the results of the simulation with experimental measurements, (b) performing a monoenergetic calibration of the WBC, with the possibility of extending the calibration to any other gamma emitter and (c) estimating the role of phantom positioning and explore its effect on the response of the WBC.…”