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

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.

Comparison between InterDosi and MCNP in the estimation of photon SAFs on a series of ICRP pediatric voxelized phantoms

In the present work, a new Monte Carlo Geant4 based code called InterDosi 1.0, was used to simulate specific absorbed fractions (SAFs) in the six reference pediatric voxel-based phantoms developed by the International Commission on Radiological Protection (ICRP). The aim of this study was to assess the ability of this code to estimate SAFs in a variety of voxel-based phantoms. A large number of photon SAFs were calculated for pairs of organs corresponding to three sources and 170 target organs/regions. A total of 108 initial photons were uniformly emitted from the source organs with eight discrete energies. In order to speed up the calculation of SAFs, Monte Carlo multithreaded simulations were started on a workstation with 12 threads, and a Geant4 tracking optimization technique was applied that consists in skipping the voxel boundaries when two adjacent voxels share the same material, which seems to reduce the simulation time by an average of approximately 36%. The results showed good agreement with the reference data produced through the MCNP 2.7 code, with average and maximum absolute discrepancies of 0.5% and 7.68%, respectively. We concluded that these results confirm the feasibility of InterDosi code to perform photon internal dosimetry calculations at a voxel level.

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.

Photon-specific absorbed fraction estimates in stylized ORNL and voxelized ICRP adult male phantoms using a new developed Geant4-based code "DoseCalcs": a validation study

When a radiotracer is injected into a patient's body as part of a nuclear medicine investigation, the entire body is exposed to the ionizing radiation emitted, which can cause biological damage. Therefore, it is important to predict the internal radiation dose to properly balance the advantages of radiological examinations. Currently, various Monte Carlo tools, such as MCNP, Geant4, and GATE, are available to estimate internal radiation dosimetry-related quantities, such as S values (S) and specific absorbed fractions (SAF). Such codes make physics easier for physicists who are experienced with computer programming; however, programming and/or simulation inputs remain a time-consuming and intensive task. In this study, we present a newly developed Geant4-based code for internal dosimetry calculations, namely "DoseCalcs". To assess the performance of the geometrical methods and computational capabilities of our developed tool, we used the GDML, TEXT, STL, and C++ methods to model the ORNL adult phantom, and a voxel-based structure to construct the ICRP adult male. SAFs in the ORNL and ICRP adult male phantoms for eight discrete mono-energetic photons with energies ranging from 0.01 to 2 MeV are calculated with DoseCalcs and compared to ORNL and OpenDose reference data. The two phantoms showed good agreement with both references, which indicates the accuracy of DoseCalcs for subsequent use in estimating internal dosimetry quantities using a variety of geometrical methods.

InterDosi Monte Carlo simulations of photon and electron specific absorbed fractions in a voxel-based crab phantom

InterDosi is a new in-house Monte Carlo code that aims at facilitating the use of the Geant4 toolkit for internal dosimetry using voxel-based phantoms. In the present work the dosimetric capabilities of this code are assessed by calculating self-irradiation specific absorbed fractions (SI-SAFs) in a voxel-based crab phantom. Recent standard human organ compositions and densities taken from ICRP Publication 110 have been used for material specifications of the four organs of a crab, namely, the heart, hepatopancreas, gills, and gonads, whereas the material assigned to the crab shell has been modeled based on literature values. The SI-SAFs were calculated for mono-energetic photons of energies between 10 and 4000 keV, and for mono-energetic electrons of energies between 100 and 4000 keV. The statistical errors corresponding to the calculated SI-SAFs were all less than 0.01%. The results obtained demonstrate that the simulated masses and volumes of the crab organs are in good agreement with those presented in the literature. In addition, the dosimetric results show that the calculated SI-SAFs are generally consistent with those reported in the literature, with some moderate differences due to differences in material specification. It is concluded that the InterDosi code can be successfully employed in internal dose estimations in small organisms, and it is suggested that material specifications specifically relating to crab tissues should be developed to provide more precise SI-SAFs.