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Journal of Radiological Protection

Calculations of S values and effective dose for the radioiodine carrier and surrounding individuals based on Chinese hybrid reference phantoms using the Monte Carlo technique

Changran Geng1,2,3, Xiaobin Tang1,2, Wei Qian1, Fada Guan4, Jesse Johns5, Haiyan Yu1,2, Chunhui Gong1,2, Diyun Shu1,2 and Da Chen1,2

1 Department of Nuclear Science and Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 211106, People’s Republic of China2 Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions, Suzhou 215123, People’s Republic of China3 Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, 02114, USA4 Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA5 Nimbus Innovations, LLC, Temple, TX 76501, USA

E-mail: tangxiaobin@nuaa.edu.cn

Received 3 May 2015, revised 22 July 2015Accepted for publication 24 July 2015Published 7 September 2015

AbstractThe S values for the thyroid as the radioiodine source organ to other target organs were investigated using Chinese hybrid reference phantoms and the Monte Carlo code MCNP5. Two radioiodine isotopes 125I and 131I uniformly distributed in the thyroid were investigated separately. We compared our S values for 131I in Chinese phantoms with previous studies using other types of phantoms: Oak Ridge National Laboratory (ORNL) stylized phantoms, International Commission on Radiological Protection (ICRP) voxel phantoms, and University of Florida (UF) phantoms. Our results are much closer to the UF phantoms. For each specific target organ, the S value for 131I is larger than for 125I in both male and female phantoms. In addition, the S values and effective dose to surrounding face-to-face exposed individuals, including different genders and ages (10- and 15-year-old juniors, and adults) from an adult male radioiodine carrier were also investigated. The target organ S values and effective dose for surrounding individuals obey the inverse square law with the distance between source and target phantoms. The obtained

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effective dose data in Chinese phantoms are comparable to the results in a previous study using the UF phantoms. The data generated in this study can serve as the reference to make recommendations for radiation protection of the Chinese patients or nuclear workers.

Keywords: Monte Carlo, computational phantoms, radioiodine, S values, effective dose

(Some figures may appear in colour only in the online journal)

1. Introduction

The internal and external dosimetry problems for radioactive isotopes of iodine usually focus on three main populations: patients accepting radioiodine diagnostics or therapy and their sur-rounding individuals (Josefsson and Forssell-Aronsson, 2014), radiopharmaceutical produc-tion workers (Cranley and Bell 1979, Sumerling et al 1983), and people exposed to nuclear power plants accidents (Bouville et al 2014). For the purpose of radiation protection, it is necessary to investigate the dose effects for the radioiodine carriers themselves as well as surrounding individuals, and generate a database for different exposure scenarios for different populations.

The radiation risks of radioiodine isotopes, especially 131I, have been investigated previ-ously. Due to the difficulty in performing in vivo measurements of the absorbed dose for internal organs following the intake of radionuclides, the internal dose is usually assessed by computational methods, such as point source methods. However, these techniques have many limitations, one of which is the neglect of the attenuation and scattering within the car-rier and the exposed individual (Siegel et al 2002, Han et al 2006). This consequently could result in the overestimation of the dose equivalent per decay by more than a factor of 2 (Shore 1992, Han et al 2013). With the development of technology in medical imaging and computer science, the combined application of computational phantoms of human bodies and Monte Carlo dose calculation methods has become a more accurate alternative to derive quantities of interest for internal dosimetry, such as the absorbed fraction (AF) and the S values of radio-nuclides, defined in the medical internal radiation dose (MIRD) schema (Bolch et al 2009).

Computational phantoms are models of human bodies used in computerized analyses (Xu and Eckerman 2010). A large number of computational phantoms have been developed over recent decades (Xu and Eckerman 2010). The first computational phantoms of hetero-geneity were the ORNL (Oak Ridge National Laboratory) stylized phantoms developed for internal dosimetry study (Snyder et al 1969). More advanced voxel phantoms were developed thereafter utilizing computed tomography or magnetic resonance imaging of human bodies and cross-sectional photograph images of cadavers (Xu et al 2000). Recently, benefiting from the flexibility of the surface modeling technique, hybrid phantoms, e.g. UF models (Geyer et al 2014), RPI models (Zhang et al 2009), and Chinese models (Geng et al 2014), were developed with the desirable features of anatomic realism and deformability. To date, not only are the computational phantoms applied in internal dosimetry, but also have been extended to medical imaging, radiation therapy, and even radiation protection problems in space radiations (Xu and Eckerman 2010).

The applications of the latest computation phantoms in internal dosimetry have been inves-tigated in previous studies. Lamart et al have reported comparisons of internal dose esti-mates for three different types of phantoms, and they concluded that the organ S values were

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underestimated in the stylized phantoms (Lamart et al 2011). Han et al calculated the organ S values and effective doses to family members exposed to adult patients treated with 131I (Han et al 2013, Han et al 2014). Other studies, such as investigating the effect of respiratory motion on internal radiation dosimetry have also been performed (Xie and Zaidi 2014).

Due to the differences of the anatomic structures between races and ages, even for the same type of organ, the dose results can be different. A few studies have been performed to investi-gate such differences (Cassola et al 2010, Kim et al 2011, Manabe et al 2014). However, the data for Chinese populations are lacking. In this study, we investigated the internal dosimetry problems using Chinese hybrid phantoms series and calculated the S values for different target organs. 125I and 131I were selected as the representative sources because they are radioiodine isotopes commonly used in both diagnostics and therapy (Robbins and Schneider 2000). Due to the high accumulation of iodine, the thyroid was selected as the source target in all of our calculations. The radiation protection to the surrounding individuals of the source carriers is also very important. Therefore, the S values and effective dose to the surrounding individuals were also investigated. In addition, we performed a thorough comparison between our results for Chinese phantoms with previous studies using other phantoms.

2. Materials and methods

2.1. Computational phantoms

A series of Chinese hybrid phantoms including three ages (10 year-old, 15 year-old, and adult) for both female and male were developed and used in this study for the Monte Carlo dose calculations. All of the phantoms were developed on the basis of the Chinese hybrid reference adult phantom (CHRAP). Details of the construction procedure for the phantom geometry and materials have been described in a previous publication (Geng et al 2014). Considering the geometry construction precision and the calculation speed in the Monte Carlo code used in this study, the phantoms were voxelized with a resolution of 0.56 × 0.56 × 0.56 cm3. The voxel-ization procedure for each organ was performed using the software binvox (Patrick 2015), and an in-house C++ code was used for the integration of the whole phantom. For each specific organ or tissue, the chemical composition is the same for the different phantoms at different ages. Tissue or organ compositions were from the data in ICRU Report No. 46 and ICRP Report No. 89 (ICRU 1992, ICRP 2002). In total six phantoms were modeled in this study. Selected female phantoms at different ages are illustrated in figure 1.

2.2. Monte Carlo configurations

The general purpose Monte Carlo particle transport code MCNP5 was used to perform the dose calculations in this study (Brown 2008). For calculating the S values in a radioiodine carrier, the male and female adult phantoms were modeled separately in each simulation. For calculating the S values and effective dose to surrounding individuals, only an adult male phantom was constructed as the radioiodine carrier but all six of the phantoms (three ages and two genders) were used as target individuals separately. The selection of only male phantom as the source carrier is arbitrary based on the fact that the thyroid is a relatively superficial organ, and thus the external exposure does not significantly rely on the structure of the surrounding anatomy. A standing face-to-face exposure scenario was constructed between the source car-rier phantom and the target phantom, shown in figure 2. The distance between them was set to 30, 60, 90, 120, and 150 cm respectively. Air is filled in the free space between phantoms.

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The universe/lattice card, which is a way to simplify the geometry input of repeated structures in MCNP5, was employed in the construction of the human voxel phantom. Considering both the energies of photons and secondary electrons and the size of the scoring geometry (tis-sues or organs), the heating number tally F6 was used as a good approximation to score the absorbed dose in different organs instead of the full transport of photons and electrons (Brown 2008). 131I and 125I radioactive isotopes were selected as sources in the simulations, and the

Figure 1. Female Chinese hybrid reference phantoms. (a) Adult, (b) 15 year-old, and (c) 10 year-old.

Figure 2. Face-to-face position between the radioiodine carrier and the exposed person.

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effects from them were investigated separately. The radioactive isotopes were assumed to be uniformly distributed within the thyroid due to the fact that the uptake of iodine from blood for thyroid is considerably greater than for all other organs, especially for persons with hyperthy-roidism whose uptake can reach 80% or more (Lamart et al 2011). However, note that for dif-ferent situations, the iodine distribution in the body should be modeled appropriately. Hence, the results for thyroid source obtained in this study can only be directly applied in the cases with hyperthyroidism persons as radioiodine carriers. The decay energy information for 125I and 131I are listed in table 1 (ICRP 1983). The number of simulated source particles was set to 5 × 108 in all simulations to make the statistical uncertainty below 5% for the dose results in all the organs of interest, recommended by ICRP to use for the calculation of effective dose (ICRP 2007). All the simulation results were normalized by the time-integrated activity of the radioisotopes (Bq · s).

2.3. Organ S values and effective dose

The MIRD schema is the established methodology for internal dosimetry (Bolch et al 2009). In this schema, the absorbed dose in a tissue or an organ, DT, is calculated by,

= × ←D A S r r ,T T S( )! (1)

where A! is the time-integrated activity of the radionuclide in the source tissue, and the S value is defined as the mean absorbed dose in target tissue, r  T, from the source tissue, rS, containing the radioisotopes. Hence, the standard unit for S value is (Gy (Bq · s)−1). The S value can be calculated by,

∑ ϕ← =

←S r r

E Y r r

m,i i i

T ST S

T( ) ( )

(2)

where, i represents the ith kind of emitted gamma rays or x-rays from the radioisotope, mT represents the mass of the target organ, Yi and Ei represent the yield and energy of the cor-responding photon per nuclear transformation, ϕ ←r ri T S( ) represents the energy absorption fraction in the target tissue from the photon emitted from the source tissue.

The effective dose, E, (ICRP 2007) is determined as the gender averaged and tissue or organ weighted summation of the equivalent doses.

∑=E w H ,T

T T (3)

Table 1. The information of photons emitted from 125I and 131I, including radiation type, energy and yield per disintegration (ICRP 1983).

125I 131I

Radiation typeEnergy (keV) Yield(%) Radiation type

Energy (keV) Yield(%)

Gamma 35.5 7 Gamma 723 1.8Kα1 x-ray 27.5 74 Gamma 637 7.3Kα2 x-ray 27.2 40 Gamma 365 81.2Five Kβ x-rays 31 26 Gamma 284 6.1

Gamma 80 2.6

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where wT is the tissue weighting factor and HT represents the equivalent dose of one specified organ. H  T is calculated as:

∑=H w DTR

R T,R (4)

where wR is the radiation weighting factor, which is unity for photons, which is the case in the current study. The values of wT can be found in ICRP Report No. 103 (ICRP 2007).

Table 2. Organ S values (Gy (Bq · s)−1) from the thyroid source for 125I and 131I in Chinese hybrid adult phantoms.

Target organs

S value for 125I (Gy (Bq · s)−1)

S value for 131I (Gy (Bq · s)−1)

Male Female Male Female

Brain 1.07E − 18 1.55E − 18 2.68E − 16 3.10E − 16Breast 2.12E − 18 3.51E − 17 1.94E − 16 3.36E − 16Stomach 2.81E − 19 6.39E − 19 7.63E − 17 8.42E − 17Small intestine 6.47E − 21 1.64E − 19 9.86E − 18 1.37E − 17Colon 7.09E − 21 1.25E − 19 1.35E − 17 1.39E − 17Heart 1.02E − 17 1.35E − 17 3.85E − 16 3.89E − 16Pancreas 4.46E − 20 1.05E − 19 4.83E − 17 5.02E − 17Salivary glands 6.21E − 16 4.76E − 16 2.79E − 15 2.28E − 15Lungs 9.06E − 17 5.55E − 17 7.42E − 16 5.83E − 16Active marrow 1.38E − 16 1.96E − 16 4.71E − 16 5.29E − 16

Table 3. Organ S values (Gy (Bq · s)−1) from the thyroid source for 131I in adult female for different types of phantoms and the ratios of S values to the Chinese phantom.

S values (Gy (Bq · s)−1)Ratio of S values to Chinese

phantom

ORNL stylized ICRP voxel UF hybrid

Chinese hybrid

ORNL/Chinese

ICRP/Chinese

UF/Chinese

Brain 4.40E − 16 2.50E − 16 3.00E − 16 3.10E − 16 1.42 0.81 0.97Breast 1.40E − 16 4.20E − 16 1.30E − 16 3.36E − 16 0.42 1.25 0.39Stomach 3.60E − 17 8.60E − 17 8.30E − 17 8.42E − 17 0.43 1.02 0.99Small intestine

6.40E − 18 2.00E − 17 2.00E − 17 1.37E − 17 0.47 1.46 1.46

Colon 7.20E − 18 1.10E − 17 1.60E − 17 1.39E − 17 0.52 0.79 1.15Heart 1.60E − 16 6.70E − 16 5.40E − 16 3.89E − 16 0.41 1.72 1.39Pancreas 4.10E − 17 5.40E − 17 5.40E − 17 5.02E − 17 0.82 1.08 1.08Salivary glandsa

3.70E − 15 1.70E − 15 2.40E − 15 2.28E − 15 1.63 0.75 1.05

Lungs 3.20E − 16 1.00E − 15 8.70E − 16 5.83E − 16 0.55 1.72 1.49Active marrow

2.70E − 16 6.80E − 16 4.90E − 16 5.29E − 16 0.51 1.29 0.93

Average ratio

NA NA NA NA 0.72 1.19 1.09

Bias NA NA NA NA 28% 19% 9%

a S values of salivary glands for ORNL stylized phantoms were calculated using the point kernel method with photon build-up factor.

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3. Results and discussion

3.1. Organ S values of the adult radioiodine carriers

The adult phantom was used to mimic a radioiodine carrier, i.e. a patient or an exposed radio-pharmaceutical production worker or a nuclear operation worker. The calculated S values (Gy (Bq · s)−1) for the organs of interest in female and male adult phantoms for both 125I and 131I are listed in table 2. For these two isotopes, the organ S value shows great dependence on the distance from the source organ (thyroid). Closer organs can receive greater dose. Most of the S values of corresponding organs in the female carrier are greater than male because of the shorter height of the female phantom with the shorter source-to-target distances. In the case of lung and salivary glands in Chinese hybrid phantoms, the S value for the male is greater than the female for both 131I and 125I. The organ S values for 125I are always lower than 131I because of the lower mean energy of photons, listed in table 1.

Lamart et al have compared S values for 131I using the UF hybrid phantoms, ICRP voxel phantoms and ORNL stylized phantoms (Lamart et al 2011). Although all these three types of phantoms are constructed based on the ICRP reference parameters, the calculation results show very large discrepancies. That can be attributed to the differences in the modeling methods. The comparisons between different types of phantoms for female and male adult phantoms are listed in tables 3 and 4. The average ratios of S values for different phantoms to Chinese phantom and the bias values show that the calculation results in this study using Chinese phan-toms are closer to those using UF phantoms. This can be explained due to the same modeling technique for these two phantom series. Nevertheless, differences still exist. For the male adult

Table 4. Organ S values (Gy (Bq · s)−1) from the thyroid source for 131I in adult male for different types of phantoms and the ratios of S values to the Chinese phantom.

S values (Gy (Bq · s)−1)Ratio of S values to Chinese

phantom

ORNL stylized ICRP voxel UF hybrid

Chinese hybrid

ORNL/Chinese

ICRP/Chinese

UF/Chinese

Brain 4.20E − 16 1.50E − 16 2.20E − 16 2.68E − 16 1.56 0.56 0.82Breast 1.00E − 16 1.40E − 16 1.30E − 16 1.94E − 16 0.52 0.72 0.67Stomach 2.20E − 17 1.20E − 16 6.50E − 17 7.63E − 17 0.29 1.57 0.85Small intestine

3.10E − 18 2.40E − 17 1.20E − 17 9.86E − 18 0.31 2.43 1.22

Colon 4.20E − 18 3.00E − 17 1.30E − 17 1.35E − 17 0.31 2.23 0.96Heart 1.30E − 16 6.40E − 16 3.80E − 16 3.85E − 16 0.34 1.66 0.99Pancreas 3.20E − 17 7.10E − 17 3.00E − 17 4.83E − 17 0.66 1.47 0.62Salivary glandsa

3.40E − 15 9.20E − 16 1.80E − 15 2.79E − 15 1.22 0.33 0.65

Lungs 2.50E − 16 9.10E − 16 6.20E − 16 7.42E − 16 0.34 1.23 0.84Active marrow

2.40E − 16 5.80E − 16 3.90E − 16 4.71E − 16 0.51 1.23 0.83

Average ratio

NA NA NA NA 0.61 1.34 0.85

Bias NA NA NA NA 39% 34% 15%

a S values of salivary glands for ORNL stylized phantoms were calculated using the point kernel method with photon build-up factor.

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phantom, the smallest ratio is 0.62 for pancreas and the largest is 1.22 for small intestine. For the female adult phantom, the smallest ratio is 0.39 for breast and the largest is 1.49 for lung. The differences between different phantoms can be attributed to several reasons. The first and foremost is due to the differences in anatomy. The height of all the three ICRP reference phantoms (ORNL stylized, ICRP voxel, and UF hybrid) is taller than the Chinese phantom. Theoretically, a shorter phantom can provide shorter distance between organs, thus resulting in larger S values. However, it is not true for all organs. For example, the S values calculated from ORNL phantoms are overall much lower than Chinese phantoms but the S values in ORNL brain and salivary glands are much higher. This cannot be simply explained by the phantom height, but may be caused by the shapes and locations of organs in different models. This is also the main reason causing the differences for the three ICRP parameters based phantoms (Lamart et al 2011). Another possible reason is the difference of the Monte Carlo codes used and the lack of data for some organs such as the salivary gland for ORNL phantoms (Lamart et al 2011). Since the salivary gland was not segmented in the ORNL stylized phantoms, the S values were calculated using the point kernel method with photon build-up factor.

3.2. Organ S values and effective dose of the surrounding individuals

The radioiodine carrier was assumed to be an adult male Chinese phantom. The target phan-toms include three different ages and two genders. For 125I and 131I sources, the variations of

Figure 3. S values and effective dose at different distances between the source carrier and the exposed person. Results are for 125I. (a) For lung, (b) for liver, (c) for gonads, and (d) effective dose.

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results with the distance between the source and target phantoms are shown in figures 3 and 4, respectively. In each figure, panel a, b, and c show S values for the lung, liver, and gonads, respectively, and panel d shows the gender-averaged effective dose. Note that the self-abortion effect of photons by the source organ and the attenuation of photons by other organs in the radioiodine carrier are considered in the Monte Carlo particle transport processes. Hence, the simulation results are much closer to the reality.

All results show that the dose roughly obeys the inverse square law with the distance. The organ S values of the exposed 10 year-old female and male phantoms are lower than others. In addition, the S values of gonads in the female phantom are lower than male because the ovaries are located within the body while the testes are located at a more exposed position.

For 131I, the effective dose per time-integrated activity to the 15 year-old phantom is the highest for any distances, and 10 year-old phantom are the lowest. The reasons are as follows: (1) the height of the 15 year-old phantom is taller than the 10 year-old phantom, (2) the body shielding for the internal organs of the 15 year-old phantom is thinner than the adult phantom. In figure 4(d), the results from Han et al using the UF phantom series are also shown as com-parisons (Han et al 2013). The same variation trend can be observed using the UF phantoms, but the effective dose values using Chinese hybrid phantoms are slightly lower. For 125I, the effective dose for the adult and the 15 year-old phantoms are almost identical. The effective dose values for 125I are lower than 131I as expected due to the lower mean energies of photons from 125I.

Figure 4. S values and effective dose at different distances between the source carrier and the exposed person. Results are for 131I. (a) For lung, (b) for liver, (c) for gonads, and (d) comparisons of effective dose between Chinese phantoms and UF phantoms.

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4. Conclusions

Monte Carlo simulations and the Chinese hybrid reference phantoms were used in this study to investigate the radioiodine (125I and 131I) related internal dosimetry problems. The S values of 131I obtained in this study are closer to the results for another series of hybrid phantoms (UF) in a previous study. The effective dose results of 131I obtained in this study are also comparable with the results from another previous study using UF phantoms for patient calculations.

Through the Monte Carlo calculations, we have made the database of the S values of radi-oiodine isotopes for the adult male and female Chinese phantoms and also generated the effec-tive dose tables for surrounding individuals of the radioiodine carriers. The data generated can be used to help hospitals and nuclear facilities to make recommendations for the isolation time for the Chinese radioiodine carriers, such as patients or nuclear workers, and their surrounding individuals.

Acknowledgment

This work was supported by National Natural Science Foundation of China (No. 11475087), the funding of Jiangsu Innovation Program for Graduate Education (No. KYLX_0265), the Fundamental Research Funds for the Central Universities (No. NS2014060), and a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institu-tions. We thank Dr Choonsik Lee et al for sharing the data for ICRP phantoms.

Reference

Bolch W E, Eckerman K F, Sgouros G and Thomas S R 2009 MIRD Pamphlet no. 21: a generalized schema for radiopharmaceutical dosimetry-standardization of nomenclature J. Nucl. Med. 50 477–84

Bouville A, Linet M S, Hatch M, Mabuchi K and Simon S L 2014 Guidelines for exposure assessment in health risk studies following a nuclear reactor accident Environ. Health Perspect. 122 1–5

Brown F B 2008 MCNP—A General Monte Carlo N-Particle Transport Code, version 5 (Los Alamos, NM: Los Alamos National Laboratory)

Cassola V, de Melo Lima V, Kramer R and Khoury H 2010 FASH and MASH: female and male adult human phantoms based on polygon mesh surfaces: I. Development of the anatomy Phys. Med. Biol. 55 133

Cranley K and Bell T K 1979 125I thyroid intakes: consideration of thyroid radiation dose, and air and water concentration limits Int. J. Appl. Radiat. Isot. 30 161–3

Geng  C, Tang  X, Hou  X, Shu  D and Chen  D 2014 Development of Chinese hybrid radiation adult phantoms and their application to external dosimetry Sci. China Technol. Sci. 57 713–9

Geyer A M, O’Reilly S, Lee C, Long D J and Bolch W E 2014 The UF/NCI family of hybrid computational phantoms representing the current US population of male and female children, adolescents, and adults—application to CT dosimetry Phys. Med. Biol. 59 5225–42

Han E Y, Bolch W E and Eckerman K F 2006 Revisions to the ORNL series of adult and pediatric computational phantoms for use with the MIRD schema Health Phys. 90 337–56

Han E Y, Lee C, McGuire L and Bolch W E 2014 A practical guideline for the release of patients treated by I-131 based on Monte Carlo dose calculations for family members J. Radiol. Prot. 34 N7–17

Han E Y, Lee C, Mcguire L, Brown T L and Bolch W E 2013 Organ S values and effective doses for family members exposed to adult patients following I-131 treatment: a Monte Carlo simulation study Med. Phys. 40 083901

ICRP 1983 Radionuclide transformations—energy and intensity of emissions, ICRP Publication Ann. ICRP 11–13

ICRP 2002 Basic anatomical and physiological data for use in radiological protection reference values, ICRP Publication 89 Ann. ICRP 32

C Geng et alJ. Radiol. Prot. 35 (2015) 707

717

ICRP 2007 The 2007 Recommendations of the international commission on radiological protection, ICRP Publication 103 Ann. ICRP 37

ICRU 1992 Photon, electron, proton and neutron interaction data for body tissues ICRU Report 46Josefsson A and Forssell-Aronsson E 2014 Dosimetric analysis of (123)I, (125)I and (131)I in thyroid

follicle models EJNMMI Res. 4 23Kim C H, Jeong J H, Bolch W E, Cho K-W and Hwang S B 2011 A polygon-surface reference Korean

male phantom (PSRK-Man) and its direct implementation in Geant4 Monte Carlo simulation Phys. Med. Biol. 56 3137

Lamart S, Bouville A, Simon S L, Eckerman K F, Melo D and Lee C 2011 Comparison of internal dosimetry factors for three classes of adult computational phantoms with emphasis on I-131 in the thyroid Phys. Med. Biol. 56 7317–35

Manabe K, Sato K and Endo A 2014 Comparison of internal doses calculated using the specific absorbed fractions of the average adult Japanese male phantom with those of the reference computational phantom-adult male of ICRP publication 110 Phys. Med. Biol. 59 1255

Patrick M 2015 (www.cs.princeton.edu/~min/binvox/) Robbins J and Schneider A B 2000 Thyroid cancer following exposure to radioactive iodine Rev. Endocr.

Metab. Disord. 1 197–203Shore R E 1992 Issues and epidemiological evidence regarding radiation-induced thyroid cancer Radiat.

Res. 131 98–111Siegel J A, Marcus C S and Sparks R B 2002 Calculating the absorbed dose from radioactive patients:

the line-source versus point-source model J. Nucl. Med. 43 1241–4Snyder  W  S, Ford  M  R, Warner  G  G and Fisher  H  L 1969 Estimates of absorbed fractions for

monoenergetic photon sources uniformly distributed in various organs of a heterogeneous phantom J. Nucl. Med. 10 5–52 (Suppl. 3)

Sumerling T, Neville R and Wrigglesworth P 1983 Determination of Iodine-125 intakes in a group of radiopharmaceutical production workers by means of thyroid radioactivity measurements Radiat. Prot. Dosim. 5 209–16

Xie  T and Zaidi  H 2014 Effect of respiratory motion on internal radiation dosimetry Med. Phys. 41 112506

Xu  X  G, Chao  T  C and Bozkurt  A 2000 VIP-Man: an image-based whole-body adult male model constructed from color photographs of the Visible Human Project for multi-particle Monte Carlo calculations Health Phys. 78 476–86

Xu  X  G and Eckerman  K  F 2010 Handbook of Anatomical Models for Radiation Dosimetry (Boca Raton, FL: Taylor & Francis)

Zhang J, Na Y H, Caracappa P F and Xu X G 2009 RPI-AM and RPI-AF, a pair of mesh-based, size-adjustable adult male and female computational phantoms using ICRP-89 parameters and their calculations for organ doses from monoenergetic photon beams Phys. Med. Biol. 54 5885–908

C Geng et alJ. Radiol. Prot. 35 (2015) 707