GEANT4 MC Research Articles

Naturally Occurring Radioactive Materials in Bracelets and Necklaces: Radiological Risk Evaluation.

A particular category of jewelry is one involving bracelets and necklaces that are deliberately made to contain naturally occurring radioactive material (NORM)—purveyors making unsubstantiated claims for health benefits from the release of negative ions. Conversely, within the bounds of the linear no-threshold model, long-term use presents a radiological risk to wearers. Evaluation is conducted herein of the radiological risk arising from wearing these products and gamma-ray spectrometry is used to determine the radioactivity levels and annual effective dose of 15 commercially available bracelets (samples B1 to B15) and five necklaces (samples N16 to N20). Various use scenarios are considered; a Geant4 Monte Carlo (Geant4 MC) simulation is also performed to validate the experimental results. The dose conversion coefficient for external radiation and skin equivalent doses were also evaluated. Among the necklaces, sample N16 showed the greatest levels of radioactivity, at 246 ± 35, 1682 ± 118, and 221 ± 40 Bq, for 238U, 232Th, and 40K, respectively. For the bracelets, for 238U and 232Th, sample B15 displayed the greatest level of radioactivity, at 146 ± 21 and 980 ± 71 Bq, respectively. N16 offered the greatest percentage concentrations of U and Th, with means of 0.073 ± 0.0002% and 1.51 ± 0.0015%, respectively, giving rise to an estimated annual effective dose exposure of 1.22 mSv, substantially in excess of the ICRP recommended limit of 1 mSv/year.

Performance study of a compact LumiCal prototype in an electron beam

The FCAL collaboration is preparing large-scale prototypes of special calorimeters to be used in the very forward region at a future electron-positron collider for a precise and fast luminosity measurement and beam-tuning. LumiCal is designed as silicon-tungsten sandwich calorimeter with very thin sensor planes to keep the Moliere radius small, facilitating such the measurement of electron showers in the presence of background. A partially instrumented prototype was investigated in a 1 to 5 GeV electron beam at the DESY II synchrotron. Thin detector planes assembled with readout electronics were installed in 1 mm gaps between tungsten plates of one radiation length thickness. Data was used to measure the longitudinal and transversal shower development. The latter was expressed in an effective Moliere radius of 8.1 mm. In addition, Geant4 MC simulations were done and compared to the data. Very good agreement was found.

Adaptive step size algorithm to increase efficiency of proton macro Monte Carlo dose calculation

PurposeTo provide fast and accurate dose calculation in voxelized geometries for proton radiation therapy by implementing an adaptive step size algorithm in the proton macro Monte Carlo (pMMC) method.MethodsThe in-house developed local-to-global MMC method for proton dose calculation is extended with an adaptive step size algorithm for efficient proton transport through a voxelized geometry by sampling transport parameters from a pre-simulated database. Adaptive choice of an adequate slab size in dependence of material interfaces in the proton’s longitudinal and lateral vicinity is investigated. The dose calculation algorithm is validated against the non-adaptive pMMC and full MC simulation for pencil and broad beams with various energies impinging on academic phantoms as well as a head and neck patient CT.ResultsFor material interfaces perpendicular to a proton’s direction, choice of nearest neighbor slab thickness shows best trade-off between dosimetric accuracy and calculation efficiency. Adaptive reduction of chosen slab size is shown to be required for material interfaces closer than 0.5 mm in lateral direction. For the academic phantoms, dose differences of within 1% or 1 mm compared to full Geant4 MC simulation are found, while achieving an efficiency gain of up to a factor of 5.6 compared to the non-adaptive algorithm and 284 compared to Geant4. For the head and neck patient CT, dose differences are within 1% or 1 mm with an efficiency gain factor of up to 3.4 compared to the non-adaptive algorithm and 145 compared to Geant4.ConclusionAn adaptive step size algorithm for proton macro Monte Carlo was implemented and evaluated. The dose calculation provides the accuracy of full MC simulations, while achieving an efficiency gain factor of three compared to the non-adaptive algorithm and two orders of magnitude compared to full MC for a complex patient CT.

Dosimetric study of GZP6 60 Co high dose rate brachytherapy source.

The purpose of this study was to obtain dosimetric parameters of GZP6 60Co brachytherapy source number 3. The Geant4 MC code has been used to obtain the dose rate distribution following the American Association of Physicists in Medicine (AAPM) TG‐43U1 dosimetric formalism. In the simulation, the source was centered in a 50 cm radius water phantom. The cylindrical ring voxels were 0.1 mm thick for r ≤ 1 cm, 0.5 mm for 1 cm < r ≤ 5 cm, and 1 mm for r > 5 cm. The kerma‐dose approximation was performed for r > 0.75 cm to increase the simulation efficiency. Based on the numerical results, the dosimetric datasets were obtained. These results were compared with the available data of the similar 60Co high dose rate sources and the detailed dosimetric characterization was discussed.

Experimental verification of a methodology for Monte Carlo modeling of multileaf collimators using the code Geant4

Among the many algorithms developed for evaluation of dose distributions in radiotherapy, the Monte Carlo methods provide more realistic results. In intensity modulated radiation therapy, significant differences in dose distributions within the fields defined by the multileaf collimator (MLC) could have significant radiobiology effects. Thus, it is important to model thoroughly the MLC to allow more accurate radiotherapy delivery. The objective of this work is to describe and to validate a methodology for modeling of MLCs using code Geant4. The Varian Millennium 120-leaf MLC was modeled using this methodology and it was experimentally verified. The leaves of the MLC were built using three types of solid (G4Box, G4Tubs and G4ExtrudeSolid) and the Boolean operation of subtraction (G4SubtractionSolid). Based on this methodology, it is possible to simulate other Varian MLC models using Geant4 or other MC code.

SU‐F‐T‐672: A Novel Kernel‐Based Dose Engine for KeV Photon Beams

Purpose:Mimicking state‐of‐the‐art patient radiotherapy with high precision irradiators for small animals allows advanced dose‐effect studies and radiobiological investigations. One example is the implementation of pre‐clinical IMRT‐like irradiations, which requires the development of inverse planning for keV photon beams. As a first step, we present a novel kernel‐based dose calculation engine for keV x‐rays with explicit consideration of energy and material dependencies.Methods:We follow a superposition‐convolution approach adapted to keV x‐rays, based on previously published work on micro‐beam therapy. In small animal radiotherapy, we assume local energy deposition at the photon interaction point, since the electron ranges in tissue are of the same order of magnitude as the voxel size. This allows us to use photon‐only kernel sets generated by MC simulations, which are pre‐calculated for six energy windows and ten base materials. We validate our stand‐alone dose engine against Geant4 MC simulations for various beam configurations in water, slab phantoms with bone and lung inserts, and on a mouse CT with (0.275mm)3 voxels.Results:We observe good agreement for all cases. For field sizes of 1mm2 to 1cm2 in water, the depth dose curves agree within 1% (mean), with the largest deviations in the first voxel (4%) and at depths&gt;5cm (&lt;2.5%). The out‐of‐field doses at 1cm depth agree within 8% (mean) for all but the smallest field size. In slab geometries, the mean agreement was within 3%, with maximum deviations of 8% at water‐bone interfaces. The γ‐index (1mm/1%) passing rate for a single‐field mouse irradiation is 71%.Conclusion:The presented dose engine yields an accurate representation of keV‐photon doses suitable for inverse treatment planning for IMRT. It has the potential to become a significantly faster yet sufficiently accurate alternative to full MC simulations. Further investigations will focus on energy sampling as well as calculation times.Research at ICR is also supported by Cancer Research UK under Programme C33589/A19727 and NHS funding to the NIHR Biomedical Research Centre at RMH and ICR. MFF is supported by Cancer Research UK under Programme C33589/A19908.

Study of the performance of a compact sandwich calorimeter for the instrumentation of the very forward region of a future linear collider detector

The FCAL collaboration is preparing large scale prototypes of special calorimeters to be used in the very forward region at a future linear electron positron collider for a precise and fast luminosity measurement and beam-tuning. These calorimeters are designed as sensor-tungsten calorimeters with very thin sensor planes to keep the Moliere radius small and dedicated FE electronics to match the timing and dynamic range requirements. A partially instrumented prototype was investigated in the CERN PS T9 beam in 2014 and at the DESY-II Synchrotron in 2015. It was operated in a mixed particle beam (electrons, muons and hadrons) of 5GeV from PS facilities and with secondary electrons of 5GeV energy from DESY-II. The results demonstrated a very good performance of the full readout chain. The high statistics data were used to study the response to different particles, perform sensor alignment and measure the longitudinal shower development in the sandwich. In addition, Geant4 MC simulations were done, and compared to the data.

Analysis of improved neutron activation technique using thick foils for application on medical LINAC environment

An improved neutron activation technique is analyzed that can be used for the characterization of the neutron field in low neutron flux environments, such as medical Linacs. Due to the much lower neutron fluence rates, thick materials instead of thin have been used. The study is focused on the calculations of basic components of the neutron activation analysis that are required for accurate results, such as the efficiency of the gamma detector used for γ-spectrometry as well as crucial correction factors that are required when dealing with thick samples in different geometries and forms. A Monte Carlo detector model, implemented by Geant4 MC Code was adjusted in accordance to results from various measurements performed. Moreover, regarding to estimate the self-shielding correction factors a new approach using both Monte Carlo and analytical approach was presented. This improvement gives more accurate results, which are important for both activation and shielding studies that take place in many facilities. A quite good agreement between the neutron fluxes is achieved; according to the data obtained a mean value of (2.13±0.34)×105ncm−2s−1 is representative for the isocenter of the specific Linac that corresponds to fluence of (5.53±0.94)×106ncm−2Gy−1. Comparable fluencies reported in the literature for similar Linacs operating with photon beams at 15MeV.

Thermal neutron response of a boron-coated GEM detector via GEANT4 Monte Carlo code

In this work, we report the design configuration and the performance of the hybrid Gas Electron Multiplier (GEM) detector. In order to make the detector sensitive to thermal neutrons, the forward electrode of the GEM has been coated with the enriched boron-10 material, which works as a neutron converter. A total of 5×5cm2 configuration of GEM has been used for thermal neutron studies. The response of the detector has been estimated via using GEANT4 MC code with two different physics lists. Using the QGSP_BIC_HP physics list, the neutron detection efficiency was determined to be about 3%, while with QGSP_BERT_HP physics list the efficiency was around 2.5%, at the incident thermal neutron energies of 25meV. The higher response of the detector proves that GEM-coated with boron converter improves the efficiency for thermal neutrons detection.

First GEANT4-based simulation investigation of a Li-coated resistive plate chamber for low-energy neutrons

A simulation study of the performance of a single-gap resistive plate chamber coated with Li-layer for the detection of low energy neutrons was performed by means of GEANT4 Monte Carlo code. Low energy neutrons were detected via 7Li(n, α) 3He nuclear reaction. To make the detector sensitive to low energy neutrons, Li- coating was employed both on the forward and backward electrodes of the converter. Low energy neutrons were transported onto the Li-coating RPC by GEANT4 MC code. A detector with converter area of 5×5cm2 was utilized for this work. The detection response was evaluated as a function of incident low energy neutrons in the range of 25MeV–100MeV. The evaluated results predicted higher detection response for the backward-coated converter detector than that of forward coated converter RPC setup. This type of detector can be useful for the detection of low energy neutrons.

Simulation response of B4C-coated PPAC for thermal neutrons using GEANT4 Monte Carlo approach

In this work we report a technique employed for the detection of thermal neutrons using the parallel plate avalanche counter (PPAC). In order to make the detector sensitive to thermal neutrons a thin layer of B4C has been coated on the forward electrode of the PPAC configuration. Upon falling on the converter coating, charged particles were generated via the B10(n,α)Li7 reaction. In this simulation study, thermal neutrons have been simulated using the GEANT4 MC code, and the response of the detector has been evaluated as a function of neutron energy. For a better understanding of the simulation response, the performance of the detector has been found using the two different physics list i.e., QGSP_BIC_HP and QGSP_BERT_HP. The obtained results predict that such boron-carbide based PPAC can be potentially utilized for thermal neutron detection. A complete description of the detector configuration and the simulation results is also presented.

The potential of attenuation-based dynamic CT beam-shaping filter modulation as a new method for radiation dose reduction in MDCT: Evaluation by Monte-Carlo simulation of spatial dose distribution

Ziele: MDCT beam-shaping filters modulate X-ray beam intensity across the fan, compensating for decreasing absorption due to shorter X-ray path lengths through patient body periphery compared to its center. The effect of replacing static MDCT beam-shaping filter geometry by filter geometry dynamically adapted to elliptical specimen in dependence of projection angle has been evaluated with regard to its potential for radiation exposure reduction. Methode: Using a Compton spectrometer, primary MDCT X-ray spectra (120kVp) have been measured at different angular distance (0°-21°) from the central ray of the fan. These have been used to calculate the geometrical shape of the bowtie filter. In addition, a theoretical model of beam-shaping filtration that can be dynamically adapted to elliptical subject geometries has been developed. Both bowtie models were implemented in a Geant4 MC simulation of MDCT, and spatial distributions of dose deposited in an elliptical water phantom (16.0cm semimajor, 12.5cm semiminor axes) were simulated for projections in steps of 15° (10^7 photons/proj., 120kVp-spectrum). Comprehensive spatial dose distributions within the phantom were reconstructed and used to evaluate relative dose reduction achievable by dynamic beam-shaping in CT. Ergebnis: Projection-angle dependent spatial distribution of dose deposition around the center of the beam created by dynamic filtration minimizes dose contributions to more peripheral voxels, leading to relative patient skin dose reductions of ~50% a.p. or ~30% lateral. Compared to a CT acquisition without any beam-shaping filter, measured static and proposed dynamic beam-shaping filter allow reducing total deposited dose by 33% and 48%, resp.. Thus, an additional radiation exposure reduction by 15% can be achieved with a filter dynamically adapted to subject shape. Schlussfolgerung: The results of the simulation study indicate that replacing static by dynamic beam shaping filtration allows for significant additional radiation exposure reduction in MDCT.

Monte carlo simulation of the response to fast neutrons of a multi-gap RPC (MRPC) by using the GEANT4 code

This article reports the simulated response to fast neutrons of a multi-gap resistive plate chamber (MRPC) by using the GEANT4 MC code. In this study, a thin polyethylene layer, which acted as the converter material for the detection of fast neutrons, was coated on the surface of the MRPC, which acts as the converter material for the detection of fast neutrons. The converter based on the polyethylene material improved the chamber’s ability to detect fast neutrons. By employing the GEANT4 MC code, fast neutrons were inserted into the converter-based MRPC chamber in the energy range of 1.0–20.0 MeV. The response of the polyethylene-coated MRPC were evaluated as a function of the neutron energy by using the QGSP BERT HP and the QGSP_BIC_HP physics list with the GEANT4 code. For a 0.13-mm converter thickness, a detection efficiency of 6.4×10−3 were found for fast neutrons with an energy of E n = 6.0 by the QGSP_BERT_HP physics list. The simulation test further confirmed that a higher response of the fast neutrons could be achieved if the converter thickness were to be increased. A detailed outline of the simulation test and the obtained results are presented.

GEANT4 Monte Carlo simulation response of parallel plate avalanche counter for fast neutrons detection

Abstract In the present study, GEANT4 based Monte Carlo codes have been employed to evaluate parallel plate avalanche counter (PPAC) response for fast neutron detection. In order to detect fast neutrons, a thin polyethylene layer is coated on the surface of the electrode of the PPAC. Neutrons entering the converter produce protons which enter the counter and are detected. Fast neutrons in the energy range of 4.0 MeV–20.0 MeV have been transported onto the PPAC surface using GEANT4 MC code. The performance of the PPAC counter has been evaluated by means of simulation by employing QGSP_BERT_HP and QGSP_BIC_HP physics lists. The detection efficiencies of polyethylene-coated PPAC are 1.69 × 10−2 and 1.86 × 10−2 using converter thickness of 1 mm and 2 mm, respectively. The obtained results are discussed in detail.

Investigation of glass-built multigap-RPC simulation response to gamma-rays up to an energy range of 1.0 GeV using GEANT4 Monte Carlo code

A new configuration of a multigap resistive plate chamber (MRPC) was implemented and tested with GEANT4 MC simulation. The glass-built 10-gap MRPC setup with each gap of 250 μm consists of several interleaved glass electrodes inside the chamber, which has an active area 3 × 3 cm2. We report the simulation response of glass-built 10-gap MRPC for gamma rays up to an energy range of 0.007 MeV to 1.0 GeV. For an isotropic gamma source using a GEANT4 MC package, sensitivities sγ < 8.22 × 10−2, sγ < 1.10 × 10−1, sγ < 1.37 × 10−1 and sγ < 1.63 × 10−1 at < 1.0 GeV by 4-gap, 6-gap, 8-gap and 10-gap glass-MRPC have been predicted, respectively. However, relatively lower sensitivities were found using the parallel gamma ray source used with the same MC package. A comparison between the glass-MRPCs and the previous bakelite-MRPCs gamma simulation results has also been performed. It has been noticed that glass-electrode RPCs give higher sensitivity response than bakelite-plates RPCs. Key words: GEANT4 Monte Carlo simulation, glass-resistive plate chambers, gamma rays sensitivity, detector response.

SU-E-T-107: Dosimetric Characteristics of a Glass Dosimeter for Proton Beam Measurements

Purpose: The purpose of this study was to investigate the dosimetric characteristics of the GD‐301 glass dosimeter for clinical dosimetry in a high‐energy proton beam and to compare it with LiF TLD‐100. Materials: The dose distribution measured with the glass dosimeter was evaluated by comparing them to those from GEANT4 MC simulation. We also compared dose measured with glass dosimeter and calculated with treatment planning system, Eclipse calculated dose of plan delivery in order to evaluate its potential as a new dosimeter in clinical proton beams. All measurements were performed in a proton beam (IBA Proton Therapy System‐Proteus 235) at the National Cancer Center in Korea. Dosimeters were irradiated in a water phantom using a stair‐like holder specially designed for this study. Maximum height was 100 mm with each step of 1 mm in ten layers. Results: Reproducibility in the 200 MeV proton beam was within 1.5% for the glass dosimeter, and within 1.7% for TLD‐chip responses. The glass dosimeter signal was linear as a function of applied dose in the range of 1—10 Gy. The fading effect of the glass dosimeter after a received dose of 2 Gy was initially found to be within 1.6% for six months. Angular dependence of the glass dosimeter was measured to be approximately 1.3% for angles ranging 80° from the beam axis using a cylindrical phantom. Depth‐dose distributions in the non‐modulated and modulated proton beams obtained with the glass dosimeter were estimated to be within 3.0% lower than those with the ionization chamber and simulation model using GEANT4 code. The difference between delivery dose calculated by the Eclipse and measured by the glass dosimeter is within 5.0%. Conclusions: Measurements comparing the glass dosimeter and TLD‐100 dosimetric characteristics demonstrated the suitability of the glass dosimeter for dose measurement in high‐energy proton beam therapy.

Recent simulation results on neutron sensitivity of new low-resistive phosphate glass electrode RPC using GEANT4 MC

The low rate capability behavior of conventional glass with resistivity ∼ 1013 Ωcm, is not acceptable in many experiments being performed in high energy physics. The usage of low bulk resistivity glass electrode in the configuration of Resistive Plate Chamber (RPC) makes it possible for such studies where high rate environment is required. The sensitivity to neutron of low-resistive glass electrode RPC has been simulated using GEANT4 Monte Carlo codes with G4 Standard and G4 Low packages. The detailed simulation studies have been performed as a function of neutron energy in the range 10−10 MeV–10 GeV. The response of the detector in LHC background environment expected in the CMS- barrel region is evaluated for the neutron energy spectrum. According to our obtained results a hit rate 0.532 Hz/cm2 has been estimated for the RPC located in RB1 station. A comparison of the simulated results with the available experimental results has also been performed.

SU‐GG‐T‐438: Dose to Medium or Dose to a Water Cavity Embedded in Medium? A Monte Carlo Study

Purpose: The target for radiotherapy is to sterilize cells by imposing damage to their DNA content. It is therefore of interest to study the relations between the dose calculated to a tissue medium, Dm,m, with an representative average atomic composition versus the dose Dn,m specifically absorbed by the cell nuclei, and the dose Dw,m to a cell nuclei surrogate represented as a water cavity embedded into tissue. The simulations were performed for six types of tissues and three different brachytherapy sources. Methods and Materials: Absorbed dose calculations were performed by GEANT4 MC code version 9.2 using the Penelope physics package. Three different sources, 192Ir to represent high energy conditions, 169Yb for intermediate energies and a low energy brachytherapy source 125I, were simulated. The photon spectra used in this study were taken from http://www.physics.carleton.ca/clrp/seed_database. The 192Ir spectra was from Nucletron, microSelectron‐HDR v2 and for 125I from Nucletron, SelectSeed, 130.002. Particle spectra for 192Ir and energy spectra for 192I were also scored to calculate the dose with different cavity theories and compare it with MC calculated doses. Results: The MC calculated Dm,m, Dw,m and Dn,m ratio shows the largest value for 125I brachytherapy source and the cortical bone material, adipose tissue and prostate tissues(ICRU). The difference between Dw,m and Dn,m is also largest for the cortical bone and 125I source. For the 192Ir source, the ratio was 1 for the soft tissues while for the cortical bone it was higher. Conclusion: Monte Carlo calculations made it possible to report the dose as absorbed dose to medium. Accurate reporting of treatment planning requires a stringent standard for dose definition. MC calculations can be used to develop conversion factors to convert dose according to different definitions for different brachytherapy sources.

Study of neutron response for two hybrid RPC setups using the GEANT4 MC simulation approach

The present article describes a detailed neutron simulation study in the energy range 10−10 MeV to 1.0 GeV for two different RPC configurations. The simulation studies were taken by using the GEANT4 MC code. Aluminum was utilized on the GND and readout strips for the (a) Bakelite-based and (b) glass-based RPCs. For the former type of RPC setup the neutron sensitivity for the isotropic source was Sn = 2.702 × 10−2 at En = 1.0 GeV, while for the latter type of RPC, the neutron sensitivity for the same source was evaluated as Sn = 4.049 × 10–2 at En = 1.0 GeV. These results were further compared with the previous RPC configuration in which copper was used for ground and pickup pads. Additionally Al was employed at (GND+strips) of the phosphate glass RPC setup and compared with the copper-based phosphate glass RPC. Good agreement with sensitivity values was obtained with the current and previous simulation results.

Simulation study on gamma-ray sensitivity of low-resistive phosphate glass electrode RPC using GEANT4 MC

The phosphate glass used as electrode in the configuration of resistive plate chamber (RPC) which improves the rate characteristics of the detector. In the present study, we describe the performance of such type of RPC. A simulation test for such detector is performed with a Monte Carlo simulator based on GEANT4. Gamma rays in the energy range 0.1 MeV–1.0 GeV were inserted on the detector surface and their simulation response is reported. The sensitivity results both for single and double-gap phosphate glass RPCs are evaluated. As an example, the obtained simulation results are applied to CMS barrel regions. Also in those regions total sensitivities and hit rates for those regions are taken.