Development and validation of a Medaka fish voxel-based model for internal ionizing radiation dosimetry.

In this paper, we present a voxel-based phantom of Medaka fish that can be used to assess the internal radiation doses that would be absorbed by different organs of this fish species if exposed to radioactive wastewater released into the ocean. The geometric model for fish was generated based on available Wavefront Object files for smooth-bodied Medaka fish organs, whereas due to the lack of Medaka fish material specification, the material model was constructed using material data appropriate to ICRP 110 adult male voxel-based phantom. Absorbed Fractions (AFs) and Specific Absorbed Fractions (SAFs) were calculated for eight organs of major interest as sources and for each organ as target at a set of discrete photon, electron, alpha and neutron energies. To validate the present model the calculated AFs in the studied organs were compared to ones obtained in similar organs in a voxel-based phantom of another teleost fish species called Limanda limanda. The results presented are consistent with the reference dosimetric data. We concluded that the Medaka model can be used in radioecology research to improve marine radiation protection.

Validation of the DoseCalcs Monte Carlo code for estimating the 18F S-values for ICRP adult and 15-year-old male and female phantoms.

Internal radiation exposure using radiopharmaceuticals, as in nuclear medicine procedures, necessitates the estimation of the S-value to determine and improve the estimates of absorbed doses in at-risk organs and tissues. The S value is defined as the absorbed dose in the target organ per unit of nuclear transformation in the source organ. It is calculated using the specific absorbed fraction, which is an important quantity that connects the deposited energy in the target and emitting source organs. In this study, we applied DoseCalcs, a new Geant4-based tool, to estimate the S values of [Formula: see text]F using nuclear data from ICRP Publication 107. Geometrical data from ICRP Publications 110 and 143 were used to select four models representing male and female phantoms for adults and 15 years old to study the variability in the S-values arising from variations in anatomy and initial energy validations, because we used the [Formula: see text] mean energy instead of the full beta spectrum. The [Formula: see text]F-released photons and [Formula: see text] from 26 source organs were tracked using the Geant4 Livermore package. Accordingly, the S-values were calculated for 141 target organs. The results for the adult male and female phantoms were compared with the OpenDose reference data. These results agreed well with OpenDose, the average ratio for self-absorption S-values was 1.015, and the average ratios for the cross-irradiation were 1.2 and 1.22 for the AM and AF, respectively. This indicates the accuracy of DoseCalcs for subsequent use in estimating [Formula: see text]F S-values using voxelized geometries.

S-values estimation of positron-emitting radionuclides in the ICRP voxel-based adult male organs using a new Geant4-based code DoseCalcs: validation study.

Identifying the organs and tissues at risk from internal radiation exposure caused by radiopharmaceuticals requires determining the absorbed dose. The absorbed dose for radiopharmaceuticals is calculated by multiplying cumulated activity in source organs by the S-value, a crucial quantity that connects the energy deposited in the target organ and the emitting source one. It is defined as the ratio of absorbed energy in the target organ per unit of mass and unit of nuclear transition in the source organ. In this study, we used a new Geant4-based code called DoseCalcs to estimate the S-values for four positron-emitting radionuclides ([Formula: see text]C, [Formula: see text]N, [Formula: see text]O, and [Formula: see text]F) using decay and energy data from International Commission on Radiological Protection (ICRP) Publication 107. Twenty-three regions were simulated as radiation sources in the ICRP voxelized adult model developed in ICRP Publication 110. The Livermore physics packages were tailored to radionuclide photon mono-energy and [Formula: see text]-mean energy. The estimated S-values based on [Formula: see text]-mean energy show good agreement with those in the OpenDose data whose values were calculated using the full [Formula: see text] spectrum. The results provide new S-values data for selected source regions; hence, they could be used for comparison and adult-patient dose estimation.

Intercomparison of S-Factor values calculated in Zubal voxelized phantom for eleven radionuclides commonly used in targeted prostate cancer therapy.

In this study we aimed at comparing various radionuclides ordinarily used in targeted prostate cancer therapy, thereby evaluating S-Factor parameter in the prostate organs as well as in its surrounding healthy tissues, namely the urinary bladder and rectum. InterDosi code version 1.1 was used to estimate S-Factor values in Zubal voxelized phantom for 11 radionuclides, namely 225Ac, 21At, 67Cu, 125I, 131I, 212Pb, 177Lu, 223Ra, 161 Tb, 227Th and 90Y. The prostate organ was considered the source of different ionizing radiation emitted by the radionuclides cited above. The results showed that among all studied alpha-emitting radionuclides, 225 Ac, 223 Ra and 227 Th provide equidistantly the highest self-irradiation S-Factors whereas, 211At provides the lowest cross-irradiation S-Factors. On the other hand, considering only beta-emitting radionuclides, it is shown that 177Lu and 90Y induce respectively lowest and highest cross-absorption S-Factors on the surrounding healthy organs. We conclude that 177Lu and 211At are more adequate for prostate radionuclide therapy because they can relatively prevent surrounding organs from radiation toxicity and at the same time provide sufficient dose to treat the prostate tumor.

Estimation of electron-specific absorbed fractions with the InterDosi code using ICRP adult female voxel-based phantom.

The International Commission on Radiological Protection (ICRP) through its publications recommends the estimation of Specific Absorbed Fractions (SAFs) using voxelized phantoms in order to assess the doses internally absorbed by organs exposed to ionizing radiation. In the present work, we report a large set of SAFs calculated using the ICRP Adult Female (ICRP-AF) phantom. The new Geant4-based code called InterDosi version 1.0 was used to simulate monoenergetic electrons of 20 different energies, ranging from 0.005 to 10 MeV, emitted uniformly from 18 different source organs. In order to estimate SAFs in 169 target organs/regions, 360 Monte Carlo multithreaded simulations were run on 32 CPUs of the HPC-MARWAN-CNRST computing grid. The calculated SAFs were compared to the recent results obtained using GATE 8.1 code and published by the OpenDose collaboration. It is shown that the obtained results are in well-agreement with the reference values, with absolute discrepancies less than 0.6% for a self-absorption condition and less than 5% in almost all energies for a cross-absorption condition. We concluded that InterDosi code might be used for dosimetry of internal electron emitters.

InterDosi simulations of photon and alpha specific absorbed fractions in zubal voxelized phantom.

In this work we used the InterDosi code to estimate photon specific absorbed fractions (SAFs) for some organs of the Zubal adult male voxelized phantom. Chemical compositions and densities of ICRP 110 adult male organs were attributed to those of the studied voxelized phantom. The SAFs of monoenergetic photons with energies ranging from 0.01 to 2 MeV, were calculated for three target regions, namely kidneys, liver, and spleen, which were the radiation source regions too. The obtained SAFs were compared to recent results obtained with the GATE code. In the GATE study, chemical compositions and densities of different organs were obtained from the ICRU report number 44. The inter-comparisons between the two studies show reasonably similar results, as 80% of the calculated SAFs are consistent within 2.5% discrepancy. This demonstrates the usefulness and applicability of the InterDosi code for internal dose calculations in a voxel-based phantom. We completed this work by studying the alpha SAFs in some organs for energies emitted by 213Bi used in targeted alpha-therapy and an analytical formula was derived for rapid alpha self-irradiation calculation in soft tissues.

EURADOS intercomparison exercise on Monte Carlo modelling of a medical linear accelerator.

BACKGROUND: In radiotherapy, Monte Carlo (MC) methods are considered a gold standard to calculate accurate dose distributions, particularly in heterogeneous tissues. EURADOS organized an international comparison with six participants applying different MC models to a real medical linear accelerator and to one homogeneous and four heterogeneous dosimetric phantoms. AIMS: The aim of this exercise was to identify, by comparison of different MC models with a complete experimental dataset, critical aspects useful for MC users to build and calibrate a simulation and perform a dosimetric analysis. RESULTS: Results show on average a good agreement between simulated and experimental data. However, some significant differences have been observed especially in presence of heterogeneities. Moreover, the results are critically dependent on the different choices of the initial electron source parameters. CONCLUSIONS: This intercomparison allowed the participants to identify some critical issues in MC modelling of a medical linear accelerator. Therefore, the complete experimental dataset assembled for this intercomparison will be available to all the MC users, thus providing them an opportunity to build and calibrate a model for a real medical linear accelerator.