Evaluation of the GEANT4 transport algorithm and radioactive decay data for alpha particle dosimetry

Khan, Ahtesham Ullah; DeWerd, Larry A.

doi:10.1016/j.apradiso.2021.109849

Cited by 10 publications

(10 citation statements)

References 27 publications

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“…These results demonstrate the ability of general-purpose MC codes to accurately calculate absorbed dose using given radioactivity. In our previous work, an extensive evaluation of the GEANT4 electromagnetic physics parameters was performed for alpha particles and the internal decay library was compared to validated databases [28]. Therefore, validation of MC transport parameters should be considered given the good agreement observed in this work between measured and MC-calculated absorbed dose.…”

Section: Discussionmentioning

confidence: 97%

“…The electromagnetic parameters for electrons were unchanged since the G4EMStandardOpt4 physics list is considered to be highly accurate for light-charged particle transport [27]. For alpha particles, the optimal electromagnetic physics parameters determined in the work of Khan and DeWerd were utilized [28]. The internal GEANT4 nuclear decay data were used to simulate the 210 Po source.…”

Section: Simulationsmentioning

confidence: 99%

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Development and evaluation of a standard for absorbed dose to water from alpha-particle-emitting radionuclides

Khan,

Radtke,

Palmer

et al. 2023

Metrologia

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Targeted radionuclide therapy (TRT) and brachytherapy with alpha particles has gained significant clinical relevance recently. Absorbed dose traceability to a standard is currently lacking in the dosimetry chain. The short range of alpha particles in water of <100 μm complicates the absorbed dose measurements in the form of significant attenuation and perturbation effects. The aim of this work was to develop and validate a standard for absorbed dose to water from alpha-particle-emitting radionuclides. A dosimetric formalism to realize surface absorbed dose to water per unit activity using a windowless cylindrical parallel-plate ion chamber (IC) was introduced. IC-based and Monte Carlo (MC)-based correction factors were calculated for a planar circular 210Po alpha-particle emitter. The measured absorbed dose to air was compared to the MC-calculated absorbed dose. A parallel-plate IC with a nominal 4 mm collector diameter composed of polystyrene-equivalent material was utilized as a standard. MC simulations were performed using the TOPAS MC code and finite source size, backscatter, and emission angle divergence correction factors were calculated by modeling the IC and the source. Multiple measurement trials were performed to measure ionization current at air gaps in the 0.3-0.525 mm range. The proposed dosimetric formalism was employed to calculate the surface absorbed dose to water from a point-like 210Po source. The recombination and polarity correction factors were measured to be <0.50% when a 150 V/mm electric field strength was applied. The MC-calculated and measured absorbed dose to air agreed within 2.05%. The finite source size and backscatter corrections were <10% with the emission angle divergence correction being in the 93-239% range. The surface absorbed dose to water was measured to be 2.8913×10-6 Gy s-1 Bq-1 with a combined uncertainty of 4.23% at k=1. This work demonstrated the ability of a windowless parallel-plate IC as a standard for absorbed dose from alpha-particle-emitting radionuclides.

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Section: Discussionmentioning

confidence: 97%

Section: Simulationsmentioning

confidence: 99%

Development and evaluation of a standard for absorbed dose to water from alpha-particle-emitting radionuclides

Khan,

Radtke,

Palmer

et al. 2023

Metrologia

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“…First, the accuracy of the PMC code depends on both the accuracy of the transport algorithm and the radioactive emission data used to produce the PMC database. Khan and DeWerd 42 recently implemented a Fano cavity test to investigate the accuracy of GEANT4's transport algorithm for 5 – 9 MeV alpha particles. They reported that by limiting the StepMax parameter value to 1 µm for both the Urban (default for alpha particles) and Wentzel‐VI multiple coulomb scattering (MCS) models, GEANT4 passed the Fano test within 0.3% (∼3% for a StepMax value of 10 µm).…”

Section: Discussionmentioning

confidence: 99%

Development of a stand‐alone precalculated Monte Carlo code to calculate the dose by alpha and beta emitters from the Ra‐224 decay chain

Hoseini‐Ghahfarokhi,

Kamio,

Mondor

et al. 2023

Medical Physics

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BackgroundRecent developments in alpha and beta emitting radionuclide therapy highlight the importance of developing efficient methods for patient‐specific dosimetry. Traditional tabulated methods such as Medical Internal Radiation Dose (MIRD) estimate the dose at the organ level while more recent numerical methods based on Monte Carlo (MC) simulations are able to calculate dose at the voxel level. A precalculated MC (PMC) approach was developed in this work as an alternative to time‐consuming fully simulated MC. Once the spatial distribution of alpha and beta emitters is determined using imaging and/or numerical methods, the PMC code can be used to achieve an accurate voxelized 3D distribution of the deposited energy without relying on full MC calculations.PurposeTo implement the PMC method to calculate energy deposited by alpha and beta particles emitted from the Ra‐224 decay chain.MethodsThe GEANT4 (version 10.7) MC toolkit was used to generate databases of precalculated tracks to be integrated in the PMC code as well as to benchmark its output. In this regard, energy spectra of alpha and beta particles emitted by the Ra‐224 decay chain were generated using GAMOS (version 6.2.0) and imported into GEANT4 macro files. Either alpha or beta emitting sources were defined at the center of a homogeneous phantom filled with various materials such as soft tissue, bone, and lung where particles were emitted either mono‐directionally (for database generation) or isotropically (for benchmarking). Two heterogeneous phantoms were used to demonstrate PMC code compatibility with boundary crossing events. Each precalculated database was generated step‐by‐step by storing particle track information from GEANT4 simulations followed by its integration in a PMC code developed in MATLAB. For a user‐defined number of histories, one of the tracks in a given database was selected randomly and rotated randomly to reflect an isotropic emission. Afterward, deposited energy was divided between voxels based on step length in each voxel using a ray‐tracing approach. The radial distribution of deposited energy was benchmarked against fully simulated MC calculations using GEANT4. The effect of the GEANT4 parameter StepMax on the accuracy and speed of the code was also investigated.ResultsIn the case of alpha decay, primary alpha particles show the highest contribution (>99%) in deposited energy compared to their secondary particles. In most cases, protons act as the main secondary particles in the deposition of energy. However, for a lung phantom, using a range cutoff parameter of 10 µm on primary alpha particles yields a higher contribution of secondary electrons than protons. Differences between deposited energy calculated by PMC and fully simulated MC are within 2% for all alpha and beta emitters in homogeneous and heterogeneous phantoms. Additionally, statistical uncertainties are less than 1% for voxels with doses higher than 5% of the maximum dose. Moreover, optimization of the parameter StepMax is necessary to achieve the best tradeoff between code accuracy and speed.ConclusionsThe PMC code shows good performance for dose calculations deposited by alpha and beta emitters. As a stand‐alone algorithm, it is suitable to be integrated into clinical treatment planning systems.

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“…Energy cuts of 20 μm (characteristic length of a cell) were applied to all particles. Cuts were reduced to 1 μm in the culture medium, from the bottom of the well up to 50 μm height and inside the detector to accurately compute dose deposition and detector signal generation 17 . Simulations were run using the QGSP_BIC_HP_EMZ physics list, particularly adapted to dosimetry in the considered energy range 15…”

Section: Methodsmentioning

confidence: 99%

“…Cuts were reduced to 1 μm in the culture medium, from the bottom of the well up to 50 μm height and inside the detector to accurately compute dose deposition and detector signal generation. 17 Simulations were run using the QGSP_BIC_HP_EMZ physics list, particularly adapted to dosimetry in the considered energy range. 15 The α-emission spectrum of the considered isotope ( 212 Pb or 223 Ra) was simulated.…”

Section: Simulation Of In Vitro Experimentsmentioning

confidence: 99%

Application of a new spectral deconvolution method for in vitro dosimetry in assessment of targeted alpha therapy

et al. 2023

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Background The improvement of in vitro assessment of targeted alpha therapy (reproducibility, comparability of experiments…) requires precise evaluation of the dose delivered to the cells. To answer this need, a previous study proposed an innovative dosimetry method based on α‐spectroscopy and a specific deconvolution process to recover the spatial distribution of 212Pb isotopes inside in vitro culture wells. Nevertheless, although promising, the deconvolution method was time consuming and only tested for a simple isotope decay chain. Purpose The purpose of this work is to propose a new matrix deconvolution method of α spectra based on a constrained‐non‐negative‐maximum‐likelihood decomposition, both faster and offering a greater modelling flexibility, allowing to study independently the kinetics of each of the daughter nuclides of complex decay chains (illustrated here with 223Ra) in in vitro culture wells. Methods Firstly, the performance of the new method was fully evaluated through Monte Carlo simulations of in vitro irradiations. Different spatial distributions of 212Pb and 223Ra, the corresponding α spectra measured by a silicon detector and the doses delivered to the cells were simulated with Geant4. The deconvolution results were then compared to the simulation results. Secondly, measurements were carried out in culture wells without cells containing 15 kBq of 212Pb or 9.3 kBq of 223Ra, placed above silicon detectors recording α spectra in real time. The matrix deconvolution was then applied to determine the spatial and temporal distribution of all α‐emitting daughters of studied isotopes. Results The matrix deconvolution was proved to recover the simulated distribution gradients, ensuring simulated doses within 3 % for both tested radionuclides, with errors on dose normally distributed around the reference value (consequently not exhibiting any bias), even in the case of complex decay chains as 223Ra. The experimental study of 212Pb and 223Ra showed highly inhomogeneous distributions and time evolution of the concentration gradients, consistent with the previous study. Furthermore, it highlighted the complex kinetics of 223Ra with different distributions of its α‐emitting daughters (219Rn, 215Po, 215At, 211Bi, 211Po). Conclusions This study validates a new deconvolution method, fast and flexible, that proved to be accurate and reliable. This method allowed to reveal the complexity of isotopes kinetics in in vitro experiments, especially with complex decay chains. Experimental dosimetry, necessary to improve reliability of in vitro studies in targeted alpha therapy, is demonstrated to be feasible with the proposed method.

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Evaluation of the GEANT4 transport algorithm and radioactive decay data for alpha particle dosimetry

Cited by 10 publications

References 27 publications

Development and evaluation of a standard for absorbed dose to water from alpha-particle-emitting radionuclides

Development and evaluation of a standard for absorbed dose to water from alpha-particle-emitting radionuclides

Development of a stand‐alone precalculated Monte Carlo code to calculate the dose by alpha and beta emitters from the Ra‐224 decay chain

Application of a new spectral deconvolution method for in vitro dosimetry in assessment of targeted alpha therapy

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