Geant4 Monte Carlo Simulation Research Articles

Li2B4O7–Bi2O3–ZrO4–CaWO4 glass system for neutron protection in neutron applications

In this study, new glass samples with a chemical composition of 40Li2B4O7+xBi2O3+(55–x)ZrO4+5CaWO4 (x = 10, 20, 30, 40, and 50 wt%) were fabricated using the melt quenching-annealing technique. Important neutron shielding parameters, such as the effective neutron removal cross-section, half-value layer, and neutron transmission factor, of all the new glass samples were calculated using the GEANT4 Monte Carlo simulation code. In addition, neutron dose measurements were performed using an 241Am–Be fast neutron source with an activity of 74 GBq and an average neutron energy of 4.5 MeV and a BF3 gaseous neutron detector. The results were compared with those of conventional shielding materials to determine the neutron absorption capabilities of the new glass materials. All the new glass samples were found to have excellent neutron shielding abilities. In particular, the GB5 sample had a high absorption capacity compared to the other samples. These new glass samples may be used as shielding materials in various radiation applications, such as generation of nuclear energy, radiation medicine, and the transport and storage of radioactive wastes.

An Experimental Validation of Spectrally Matched Neutron Detection Systems Using 3He and BF3

Here we perform the matching of neutron counts in two detector gasses through capture reactions and radiation transport–optimized moderating materials. One of our detectors uses helium-3 (3He) gas and has been widely used as a neutron detection material in proportional detector tube designs. This study examines boron trifluoride (BF3) as a potential gas for neutron detection in place of 3He based on a previously studied “spectrally matched” design derived from deterministic adjoint analyses that closely mimic the spectral response of 3He. The integrated spectral response of each tube, i.e., the count rate, is calculated and measured at various distances from an isotropic neutron source where similar “total sources” are achieved in either detection system. Our results show the integrated spectral response of a dual BF3 tube detector was within 10% of a single 3He tube when exposed to a similar source. GEANT4 Monte Carlo simulations were used to calculate the total source for each detector and showed count rates within 5% of those produced by MCNP, providing a strong confidence in its behavior in the thermal energy regime. We provide results in this study to partially validate the replacement based on the spectrally matched design, which will lead to further validation through the utilization of multiple neutron spectra via simulated and experimental studies.

Radiation shielding performance of metal oxides/EPDM rubber composites using Geant4 simulation and computational study

This paper aimed to evaluate the shielding performance of ethylene propylene diene monomer (EPDM) rubber composites filled with 200 phr of different metal oxides (either Al2O3, CuO, CdO, Gd2O3, or Bi2O3) as protective materials against gamma and neutron radiations. For this purpose, different shielding parameters, including the linear attenuation coefficient (μ), mass attenuation coefficient (μ/ρ), mean free path (MFP), half value layer (HVL), and tenth value layer (TVL), were calculated in the energy range between 0.015 and 15 MeV by using the Geant4 Monte Carlo simulation toolkit. The simulated μ/ρ values were validated by the XCOM software to examine the precision of the simulated results. The maximum relative deviation between the Geant4 simulation and XCOM was not greater than 1.41%, confirming the accuracy of the simulated results. Based on μ/ρ values, other significant shielding parameters such as effective atomic number (Zeff), effective electron density (Neff), equivalent atomic number (Zeq), and exposure buildup factor (EBF) were also computed to explore the potential usage of the proposed metal oxide/EPDM rubber composites as radiation protective materials. The study demonstrates that the gamma-radiation shielding performance of the proposed metal oxide/EPDM rubber composites are increasing in the order of EPDM < Al2O3/EPDM < CuO/EPDM < CdO/EPDM < Gd2O3/EPDM < Bi2O3/EPDM. Furthermore, three sudden increases in the shielding capability in some composites occur at 0.0267 MeV for CdO/EPDM, 0.0502 MeV for Gd2O3/EPDM, and 0.0905 MeV for Bi2O3/EPDM composites. This increase in the shielding performance is due to the K absorption edges of Cd, Gd, and Bi, respectively. Regarding the neutron shielding performance, the macroscopic effective removal cross-section for fast neutrons (ƩR) was evaluated for the investigated composites using MRCsC software. The highest ƩR is obtained for Al2O3/EPDM, while the lowest ƩR is obtained for EPDM rubber with no metal oxide content. According to the obtained results, the investigated metal oxide/EPDM rubber composites can be employed as comfortable clothing and gloves designed for workers in radiation facilities.

Calculation of surface spectral irradiance using the Geant4 Monte Carlo toolkit

The spectral direct normal irradiance (DNI) of the surface spectral irradiance, with a spectral resolution of 1 nm in the range of 280–1600 nm, and 5 nm in the range of 1600–3000 nm, has been calculated for the first time with the Geant4 Monte Carlo simulation toolkit using the US Standard Atmosphere 1976 model and the reference extraterrestrial solar spectrum SOLAR-ISS. The atmospheric attenuation of DNI has been studied with and without aerosols. In the presence of aerosols corresponding to 10 km visibility, the total solar DNI attenuation can reach about 84% in the UV domain, 56% in the visible domain and 35.08% in the rest of the infrared domain. The Geant4 results have been compared to those calculated by the MYSTIC code of LibRadtran package and the Beer–Lambert law under the same atmospheric conditions. The average relative transmittance difference between Geant4 and MYSTIC is of the order of few percent in the entire solar spectrum. In the case of atmosphere with aerosols corresponding to 23 km visibility, the most important average of the relative difference between Geant4 and MYSTIC transmittances is about 7.5% in the UV domain and stays between 1.19% and, 3.31% in the rest of the spectrum. More importantly, in this last case of the atmosphere, the values of the spectral transmittance of Geant4 remain intermediate between those of MYSTIC and Beer–Lambert law in the entire visible range up to 800 nm.

Design and characterization of AmLi neutron sources for the LZ experiment

In this paper we describe the development, testing, and characterization of three low-emission rate AmLi neutron sources. The sources are used to calibrate the nuclear recoil response of the LUX-ZEPLIN (LZ) dark matter experiment. The sources' neutron emission rate was measured using 3He proportional tubes. The sources' gamma emissions were characterized using a high-purity germanium (HPGe) detector. Source-validated Geant4 Monte Carlo simulations allowed to calibrate the Ge and neutron detectors' responses.

The Zenith‐Angle Dependence of the Downward Radiation Dose Rate on the Martian Surface: Modeling Versus MSL/RAD Measurement

AbstractThe Radiation Assessment Detector (RAD) on board the Mars Science Laboratory's Curiosity rover has been monitoring the surface radiation environment on Mars for just over 10 years. It has been found by Wimmer‐Schweingruber et al. (2015, https://doi.org/10.1002/2015gl066664) that within the narrow view cone of RAD, the directionality of the radiation field is close to but not completely isotropic. In order to better understand the directionality of the surface radiation over a wide range of zenith angles (θ), we perform a three‐dimensional Geant4 Monte Carlo simulation to derive the θ‐dependence of the surface dose rate. The results show that galactic cosmic ray protons, coming in at θ ∼ 74° make the greatest contribution to the surface dose. For helium ions, this angle is at around 46°. This is a consequence of the increasing column depth at larger zenith angles and the complex interplay of the destruction of primary and the creation of secondary particles as the primary cosmic ray interacts with the Martian atmosphere. We also compared the simulated results with the RAD measurements and found a reasonable agreement. Our results are important for future human exploration of Mars, for instance, to estimate the effectiveness of radiation shielding of a given geometry or for optimizing the radiation shielding design of a Martian habitat.

Investigation of gamma radiation shielding characteristics of bismuth reinforced ternary composites in wide photon energy region

The aim of this study is to evaluate gamma ray shielding properties for bismuth doped barite-based ternary polymer composite materials. In the first stage of the study, a polymer matrix was prepared by combining orthophthalic unsaturated polyester resin (OUP), Methyl Ethyl Ketone Peroxide (MEKP) and Cobalt Octoate (6%) (Co-6). Then, barite and bismuth were added in certain proportions as filler material into this polymer matrix and thus ternary composites were produced. Experimental studies for the produced samples were carried out in narrow beam geometry using HPGe detector and 133Ba, 22Na, 137Cs, 60Co radioactive sources which emit photons between 276.4 and 1332.5 keV energy. To determine the gamma ray shielding properties of the produced ternary composites, radiation protection efficiency (RPE), linear attenuation coefficient (μ), mass attenuation coefficient (μ/ρ), half value layer (HVL), tenth value layer (TVL), mean free path (MFP), effective atomic number (Zeff), effective electron density (NE) parameters were obtained. Experimental results were compared with theoretical results obtained with WinXCOM software and GEANT4 Monte Carlo simulation code. Experimental and theoretical results were found to be compatible with each other. According to obtained results, it was found that the sample with the best shielding property among the prepared samples was BaBi50 coded sample.

Adding the X‐ray Bragg reflection physical process in crystal to the Geant4 Monte Carlo simulation toolkit, part I: reflection from a crystal slab

AbstractX‐ray diffraction from a solid crystal shows the wave nature of photons. It is an important electromagnetic (EM) physics process when X‐ray photons interact with a crystal. Bragg diffraction, often called Bragg reflection, is a special case of the general form of X‐ray diffraction, known as Laue diffraction. When the Bragg's law is met, the incident photon beam is reflected from the crystal plane behaving as a specular reflection at the Bragg angle. However, the Bragg reflection physical process has not been integrated into the general‐purpose Monte Carlo simulation toolkit Geant4 for particle physics. In the current study, we developed a new EM physical process class “G4CrystalBraggReflection” and a new EM physical model class “G4DarwinDynamicalModel” for modeling the Bragg reflection physical process within a crystal. We added the Bragg reflection physical process to the EM physics category of Geant4. The preliminary results of photon tracking in a silicon crystal slab have shown the feasibility of simulating the Bragg reflection process in addition to the standard EM processes in the framework of Geant4.

G4XRTube: A Geant4-based Monte Carlo application for X-ray tube simulation

This paper focuses mainly on the generation of X-rays in the X-ray tubes and their utilization in imaging applications. In this work, the Geant4 Monte Carlo simulation toolkit was used to develop an application for simulating the production of X-rays in X-ray tubes. This Geant4-based Monte Carlo application generates X-ray spectra depending on anode angle, tube voltage, filter and anode material. In addition to X-ray spectra, G4XRTube can be used, for instance, for the prediction of half-value layer (HVL) and investigation of anode heel effect. The utilization of G4XRTube can also be extended to include other fields such as radiation protection, shielding, dosimetry and investigation of the performance of X-ray tubes and detectors. The results obtained in this work with G4XRTube were validated against existing data in the literature. Specifically, we compared our results with experimental literature data and TASMICS, SpekCalc, and SpekPy codes. The comparison shows a good agreement between G4XRTube results and other data.

Differential die-away technology applied to detect special nuclear materials

Differential die-away analysis (DDAA) technology is a special nuclear material (SNM) active detection analysis technology. Be a nuclear material shielded or not, the technology can reveal the existence of nuclear materials by inducing fission from an external pulsed neutron source. In this paper, a detection model based on DDAA analysis technology was established by geant4 Monte Carlo simulation software, and the optimal sensitivity of the detection system is achieved by optimizing different configurations. After the geant4 simulation and optimization, a prototype was established, and experimental research was carried out. The result shows that the prototype can detect 200 g of 235U in a steel cylinder shield that's of 1.5 cm in inner diameter, 10 cm in thickness and 280 kg in weight.

Prompt gamma ray detection and imaging for boron neutron capture therapy using CdTe detector and novel detector shield - Monte Carlo study.

For boron neutron capture therapy (BNCT), the improvements in patient dosimetry will require information about the spatial variation of 10 B concentration in the tumor and critical organs. A non-invasive approach, based on the detection of prompt gamma (PG) rays from the BNC reaction, may be well-suited to obtain such information. The detectability of the BNC PG rays has been shown experimentally utilizing energy-resolving cadmium telluride (CdTe) detectors. However, the feasibility of this approach under the clinically relevant conditions of BNCT is currently unknown. The present work aimed to investigate the aforementioned feasibility by performing Monte Carlo (MC) simulations under the phantom irradiation geometry relevant to accelerator-based BNCT (a-BNCT). Especially, this investigation focused on demonstrating the enhanced detection of the BNC PG rays using a novel neutron shield for CdTe detectors. Upon demonstrating the efficacy of the proposed detector shield, the BNC PG ray-based quantitative imaging of clinically relevant concentrations of 10 B was also demonstrated. The Geant4 MC simulation toolkit was used to model the phantom irradiation by an epithermal neutron beam as well as the detection of the BNC PG rays from the phantom by CdTe detectors with and without the proposed gadolinium (Gd)-based detector shield. It was also used to model the BNC PG ray-based quantitative imaging of 10 B concentrations under a-BNCT scenarios. Each model included a 20cm-diameter/24cm-height cylindrical PMMA phantom containing 10 B inserts at various concentrations. Arrays of CdTe crystals of 5×5×1 mm3 each (up to 120 in the case of a ring detector) were modeled for acquiring the BNC PG ray signals and quantitative imaging. According to the MC simulations, thermalized neutrons from the phantom were found to reach the CdTe detector and captured by Cd and Te, resulting in the gamma ray background noise that directly interfered with the BNC PG ray signal. The proposed Gd-based detector shield was found to be highly effective in shielding thermal neutrons from the phantom, thereby reducing the unwanted gamma ray background noise. Owing to this shield, the detection of as low as seven parts-per-million (ppm) of 10 B within the phantom of clinically relevant size was possible using 20 billion incident neutron histories. Furthermore, quantitative imaging of 10 B distributed at low concentration (down to 50ppm) within the phantom was demonstrated using computed tomography (CT) simulations with 16 billion incident neutron histories per angular projection. The 10 B detection limit (7.5ppm) was also estimated using the reconstructed CT image. Both 10 B detection limits determined from this investigation are deemed clinically relevant for BNCT. The proposed Gd-based detector shield played an essential role for achieving the currently reported 10 B detection limits. Overall, the present MC simulation work demonstrated highly sensitive BNC PG ray detection and imaging under a-BNCT scenarios using CdTe detectors coupled with a novel detector shield.

Reaction studies with neutron-rich light nuclei at the upgraded SEC Device: Exploring the excited structure of 11Li

The 11Li nucleus is considered the best example of a two-neutron halo nucleus. While the structure of the ground state is well established there is still a significant debate regarding its excited states despite of the multiple experiments realised mainly from the excitation of the ground state of 11Li that is rather complex. We propose a novel approach, to directly feed the different excited states of 11Li by the (t,p) reaction as 9Li has a simpler structure. We will employ a 9Li beam produced at ISOLDE and post-accelerated by HIE-ISOLDE to energies of 7 MeV/u to impinge on a 3H-target located at the upgraded SEC station, this station contains a new particle detection set up: composed of 5 Si-particle telescopes in a pentagon configuration with end caps consisting of 2 CD Si detectors downstream and 1 CD upstream has been prepared to offer the maximum angular coverage and resolution. Geant4 Monte Carlo simulations with the efficiency of the setup is presented in the following proceeding.

Estimation of Geometric Factors for the Particle Detecting Instruments of the Geostationary Satellite GK2A at 128.2°E Longitude Based on Observations of the Outer Radiation Belt During Geomagnetically Quiet Periods

AbstractWe present a method to determine energy‐dependent geometric factors for charged particle instruments in electron energy range of 125–2,200 keV aboard the geostationary satellite GEO‐KOMPSAT‐2A (GK2A), stationed at 128.2°E longitude. As deduced from the GEANT4 Monte Carlo simulation, the response function of the instrument in a matrix form was employed to undertake forward‐fitting of the differential energy spectra against various functions such as the double Maxwellian (DM), relativistic kappa (KP), and power‐law (PL). Thereby, we determined the energy‐dependent geometric factors for each energy channel and instrument. The forward‐fitting method was performed for a selected period of geomagnetically quiet days from May to November 2019, by applying stringent conditions to geomagnetic indices and the residual from the fit. It was found that the KP and DM functions provided better fits overall, whereas the PL function yielded considerably worse fits to the measurements. For the KP and DM functions, the validity of the geometric factors was examined against the distributions of the measured count rates and inferred model fluxes. The estimated model parameters, such as the spectral index from the KP function or the temperature from the DM functions, were also analyzed. The present study shows that the instruments provided quantitative observations of the outer radiation belt at a vantage point of 128.2°E longitude and allowed for a simple and reliable means to obtain electron fluxes based on combinations of results from numerical simulation, ground calibration, and space measurements.

A proton-recoil track imaging system for fast neutrons: the RIPTIDE detector

Fast neutron detection is often based on the neutron-proton elastic scattering reaction: the ionization caused by recoil protons in a hydrogenous material constitutes the basic information for the design and development of a class of neutron detectors. Although experimental techniques have continuously improved, proton-recoil track imaging remains still at the frontier of n-detection systems, due to the high photon sensitivity required. Several state-of-the-art approaches for neutron tracking by using n-p single and double scattering — referred to as Recoil Proton Track Imaging (RPTI) — can be found in the literature. So far, they have showed limits in terms of detection efficiency, complexity, cost, and implementation. In order to address some of these deficiencies, we propose the design of RIPTIDE, a novel recoil-proton track imaging detector in which the light output produced by a fast scintillator is used to perform a complete reconstruction in space and time of the interaction events. The proposed idea is viable thanks to the dramatic advances in low noise and single photon counting achieved in the last decade by new scientific CMOS cameras as well as pixel sensors, like Timepix or MIMOSIS. In this contribution, we report the advances on the RIPTIDE concept: Geant4 Monte Carlo simulations, light collection tests as well as state-of-the-art approach to image readout, processing and fast analysis.

Automatic organ completion with image stitching for personalized radiation dosimetry in CT examinations.

Computed tomography (CT) image-based patient-specific voxel-based dosimetry has difficulties complementing missing tissues for organs located partially inside or completely outside the image volume. Previous studies constructed patient-specific whole-body models by rescaling reference phantoms or extending regional CT images with manually adjusted phantoms. This study proposes a methodology for automatic organ completion of regional CT images for CT dosimetry using a stitching approach. Virtual clinical trials were performed by truncating whole-body CT images to generate virtual clinical chest and abdominopelvic CT images. Corresponding anchor images for each patient were selected according to sex and similarity of the axial length and water equivalent diameter of the virtual regional CT images. Automatic image stitching was performed by transformation initialization and iteration, while the stitched CT images and organ atlas were used in GPU-based Geant4 Monte Carlo simulations to generate a radiation dose map and absorbed organ dose. To evaluate the performance of the stitching model in radiation dosimetry, organ mass differences and Jaccard's coefficient of stitched and rescaled anchor images were calculated, and the radiation doses were compared among the corresponding values from the VirtualDose®, original whole-body CT, stitching model, regional CT, registration-based rescaling method, and WED-based rescaling method. The anatomical accuracy of stitched images was significantly improved. For organs partially inside the image volume, organ dose estimation from the stitching model could be more accurate than that reported in previous studies. The absolute differences in effective dose from the stitched images were 6.55% and 4.81% for chest and abdominopelvic CT scans, respectively. The proposed automatic stitching model partially complements organs inside or outside the CT scan range and provides more accurate anatomical representations for radiation dosimetry than traditional phantom rescaling methods.

Polarizability, optical electronegativity, and gamma transmission ability of newly developed Bi2O3–GeO2-Eu2O glasses

Because radiation is used in advanced technologies on a daily basis, whether in medicine or nuclear facilities, a proper shield is required to ensure the safety of workers and the public. In this paper, a newly developed Bi2O3+GeO2+Eu2O glass system was reported as a new candidate for potential radiation shielding applications. Several optical parameters such as polarizability, optical transmission, refractivity, and optical electronegativity were determined and discussed in detail for the involved glass specimens. The radiation shielding studies for the present glass samples were performed via Geant4 Monte Carlo simulations and several theoretical approaches based on the Phy-X platform. The results of gamma studies show that the maximum values of attenuation factors, namely MACs, are 85.1464, 85.0830, 85.0201, and 84.9579 cm2/g at 0.015 MeV for BGE0.5, BGE1.0, BGE1.5, and BGE2.0, respectively. The neutron shielding studies reveal that as Eu2O3 increased from 0.5 to 2 mol%, the thermal cross section increased from 47.63 to 184.53 1/cm. Furthermore, the investigated glasses are found to be more shielding than RS-253-G18, ordinary concrete, barite concrete, RS-360, and are very close to Pb-based glass.

A simple system for measuring the transmittance curve of x-ray filters at low x-ray energies.

To prevent the x-ray detectors from the interference of optical photons, x-ray filters are widely used in x-ray space missions. As the flux of low energy x-rays would be significantly attenuated by the filters, it is important to derive the transmittance of the filters below 10keV. In this paper, we present a simple experimental apparatus and data processing method to measure the transmittance curve of x-ray filters in the energy range from 1.6 to 10keV. The measured spectra were further processed with Geant4 Monte Carlo simulation results and a direct demodulation algorithm. The obtained transmittance is in good accordance with the theoretical calculation and the synchrotron radiation test result, which proves that the proposed system with the algorithm is a reasonable way to characterize the x-ray transmittance performance of filters above 1.6keV.

Monte Carlo GEANT4 Simulation Approach in Analyzing Radiation Shielding Parameter of Lombok Pumice

The linear attenuation coefficient (LAC), mean free path (MFP), half-value layer (HVL), and the radiation protection efficiency (RPE) parameters of Lombok pumice powder from 3 different regions (Ijobalit, Setangi beach, and Lingsar) have been analyzed. The radiation parameter analysis was carried out to determine the pumice that potential as a raw material of radiation shielding composite. The Monte Carlo simulation using the GEANT4 toolkit was applied to analyze those parameters using a gamma-ray transmission measurement for the photon energies of 57Co, 133Ba, 54Mn, 137Cs, 60Co, 65Zn, 22Na and 40K. The GEANT4 simulation results were compared to the XCOM theoretical calculation and show that the linear attenuation coefficient parameter has a good agreement with the XCOM results based on the determination coefficient of the correlation graph (R2 = 0.998) between those 2 approaches methods. Setangi beach pumice has a smaller LAC parameter than Ijobalit pumice and Lingsar pumice. The MFP and HVL parameter of the Setangi beach pumice indicate the absorption ability of gamma photons is low. In the low gamma energy 0.122 MeV, Ijobalit pumice and Lingsar pumice have more than 50 % RPE and are better used as a raw material of radiation shielding composite.&#x0D; HIGHLIGHTS&#x0D; &#x0D; New lead-free shielding materials of radiation becomes a critical concern in the investigation of raw shielding material&#x0D; GEANT4 Monte Carlo simulation and XCOM theoretical calculation was conducted to analyse the radiation LAC parameter&#x0D; Radiation parameters analysis of Lombok Pumice show that Ijobalit pumice and Lingsar pumice have more than 50 % RPE and are better used as a raw material of radiation shielding composite&#x0D; &#x0D; GRAPHICAL ABSTRACT

Small beams, fast predictions: a comparison of machine learning dose prediction models for proton minibeam therapy.

Dose calculations for novel radiotherapy cancer treatments such as proton minibeam radiation therapy is often done using full Monte Carlo (MC) simulations. As MC simulations can be very time consuming for this kind of application, deep learning models have been considered to accelerate dose estimation in cancer patients. This work systematically evaluates the dose prediction accuracy, speed and generalization performance of three selected state-of-the-art deep learning models for dose prediction applied to the proton minibeam therapy. The strengths and weaknesses of those models are thoroughly investigated, helping other researchers to decide on a viable algorithm for their ownapplication. The following recently published models are compared: first, a 3D U-Net model trained as a regression network, second, a 3D U-Net trained as a generator of a generative adversarial network (GAN) and third, a dose transformer model which interprets the dose prediction as a sequence translation task. These models are trained to emulate the result of MC simulations. The dose depositions of a proton minibeam with a diameter of 800μm and an energy of 20-100 MeV inside a simple head phantom calculated by full Geant4 MC simulations are used as a case study for this comparison. The spatial resolution is 0.5 mm. Special attention is put on the evaluation of the generalization performance of the investigatedmodels. Dose predictions with all models are produced in the order of a second on a GPU, the 3D U-Net models being fastest with an average of 130 ms. An investigated 3D U-Net regression model is found to show the strongest performance with overall 61.0 0.5% of all voxels exhibiting a deviation in energy deposition prediction of less than 3% compared to full MC simulations with no spatial deviation allowed. The 3D U-Net models are observed to show better generalization performance for target geometry variations, while the transformer-based model shows better generalization with regard to the protonenergy. This paper reveals that (1) all studied deep learning models are significantly faster than non-machine learning approaches predicting the dose in the order of seconds compared to hours for MC, (2) all models provide reasonable accuracy, and (3) the regression-trained 3D U-Net provides the most accuratepredictions.

PO26 Presentation Time: 7:40 AM: Dosimetry Accuracy of a Model-Based Dose Calculation Algorithm in Modeling a Novel Direction Modulated Brachytherapy Tandem Applicator for the Cervical Cancer

<h3>Purpose</h3> A novel shielded tandem applicator for the direction modulated brachytherapy (DMBT) was previously introduced, which showed capability to improve the coverage of nonuniform targets and organs at risk in cervical cancer. This applicator has been recently modeled in a commercial treatment planning system (TPS - BrachyVision ACUROS^TM (BVA)), a Model based Dose Calculation algorithm (MBDCA), for the clinical research. In this study, we aim to benchmark the accuracy of the TPS in modeling the DMBT tandem using Monte Carlo (MC) simulations. <h3>Materials and Methods</h3> The DMBT tandem applicator, made of an MR compatible tungsten alloy with six symmetrical grooves covered by a sheath of PEEK plastic, was simulated in GEANT4 MC code. Subsequently, two scenarios were created using the BVA TPS and reproduced by GEANT4 MC simulations, including ‘source at the center of the water phantom' and ‘source at the middle of the applicator' for the cubical phantoms with dimensions of (20 cm)³, (30 cm)³, and (40 cm)³. A track length estimator (TLE) was then utilized to estimate the dose deposited inside the water phantoms and 2D/3D scoring were performed. Volumetric dose comparisons of the TPS against MC results were further implemented. <h3>Results</h3> There were different level of agreements between the TPS and MC results for the different phantom sizes. The best agreement, however, was achieved for the phantom (40 cm)³, such that the dose difference fell in the intervals [0% 8.5%] and [-6.5% 6.5%] in 95% of the voxels, for the ‘source at the center of the water phantom' and ‘source at the middle of the applicator', respectively. In addition, the dose difference was within for all phantoms, within 5 cm from the center of the HDR sources. <h3>Conclusions</h3> The results of this study indicated that the accuracy of the TPS in dose calculation depends on the phantom size. Nevertheless, it seems the TPS could still provide satisfactory accuracy inside the area of clinical importance.