Radioprotection 2024 , 59 ( 4 ), 296 – 305 © A . Bouzouita et al ., Published by EDP Sciences , 2024 https :// doi . org / 10.1051 / radiopro / 2024030
Available online at : https :// www . radioprotection . org /
ARTICLE
Voxel-based Monte Carlo simulation of human external exposure to terrestrial gamma radiation
A . Bouzouita 1 , B . Askri 2 ,* , K . Manai 1 and A . Trabelsi 1 , 3 1 Faculty of Sciences of Tunis , University of Tunis El Manar , 2092 Tunis , Tunisia . 2 Research Laboratory on Energy and Matter for Nuclear Science Development ( LR16CNSTN02 ), National Center for Nuclear Science
and Technologies , Sidi Thabet Technopark 2020 , Tunis , Tunisia . 3 National Center for Nuclear Science and Technologies , Sidi Thabet Technopark 2020 , Tunis , Tunisia .
Received : 13 March 2024 / Accepted : 31 July 2024
Abstract – Organ absorbed doses are calculated for human exposure to terrestrial gamma radiation using a two-stage voxel-based Monte Carlo simulation in which the human body is represented by the voxel ICRP110 phantoms integrated in the Geant4 Monte Carlo code . The transport of photons in the soil-air medium is optimised by using a proven optimised geometry that allows tracking only those photons that have a high chance of reaching the standing reference phantom on the ground . For an optimal tracking within the voxel phantom , a nested parameterisation navigation technique implemented in Geant4 is applied . The organ-absorbed doses and the correspondent effective dose are calculated for the natural radioactive series of 238 U and 232 Th and for the 40 K and 137 Cs radionuclides . The results are compared to published studies that used the less precise mathematical based MIRD phantoms and to results derived from the ICRP144 report using the most advanced voxel phantom . The degree of agreement and the source of discrepancy between the realistic voxel model of the human body and the mathematical model used in the literature are analysed .
Keywords : voxel phantom / Monte Carlo / radioactive series / organ dose conversion factors
1 Introduction
Accurate dosimetry is essential for establishing protection standards for human exposure to radioactive pollutants . Access to radioactivity level in the soil is important to derive the effective dose received by the population . The effective dose , introduced in the International Commission on Radiological Protection publication 60 ( ICRP , 1991 , 2007 ), is the riskrelated quantity in radiation protection and is defined as the weighted average of the organ equivalent doses . Organ equivalent doses must be calculated using dose conversion factors , also called DCF and expressed in nSv h �1 per Bq Kg �1 , to provide a reference to the radioactivity concentration in the soil . Given the complexity of experimentally determining DCFs , Monte Carlo simulation is a powerful tool for calculating these DCFs .
Organ DCFs for external exposure to soil radioactivity are scarce . Most literature focuses on the calculation of the effective dose ( Jacob et al ., 1986 ; Saito , 1991 ; Eckerman and Ryman , 1993 ; Krstic and Nikezic , 2009 , Askri et al ., 2023 ) and very few works are dedicated to the detailed calculation of
* Corresponding author : boubaker . askri @ cnstn . rnrt . tn organ doses ( Zankl et al ., 1997 ; Sanusi et al ., 2021 ). Stylized mathematical phantoms were used in the Monte Carlo calculation of DCFs for external exposure to gamma radiation emitted from sources distributed in the ground . This includes the ORNL phantom proposed by Oak Ridge National Laboratory for modeling the human body based on analytical equations and the anthropomorphic phantom MIRD proposed by the Internal Radiation Dose Committee ( Snyder et al ., 1978 ; Kramer et al ., 1982 ), which is a Series of volumes and curves created to adjust the dimensions and weight of the ICRP reference man . Although mathematical phantoms provide a good approximation of the human body , they do not reflect the actual complexity of human anatomy , which is characterized by detailed structures at various scales . Recently the International Commission on Radiological Protection ( ICRP ) adopted the voxel models for their computational phantoms to represent the reference computational phantoms of the human body in adult male ( RCP-AM ) and adult female ( RCP-AF ) ( ICRP , 2009 ). The ICRP-110 reference phantoms are a set of voxel models of the human body created from patient computed tomography ( CT ) images and adjusted to match reference data from ICRP Publication 89 ( ICRP , 2002 ). When compared to previous stylized mathematical phantoms ( Johnson and Dunford , 1985 ; ICRP , 2009 ), these voxel
This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( https :// creativecommons . org / licenses / by / 4.0 ), which permits unrestricted use , distribution , and reproduction in any medium , provided the original work is properly cited .