Computation of relative biological effectiveness of low-energy electrons release in gadolinium neutron capture therapy based on microdosimetry / 中华放射医学与防护杂志

Objective:To calculate the relative biological effectiveness (RBE) value of the released low-energy electrons in gadolinium neutron capture therapy ( 157GdNCT) based on microdosimetry. Methods:The Monte Carlo (MC) code Geant4-DNA package was used to simulate the energy deposition distribution and microdosimetry parameters of low-energy electrons released during gadolinium neutron capture treatment in different sensitive target volumes and physical models on track structures. On this basis, RBE value was obtained based on the microdosimetry kinetic model (MKM).Results:The low-energy electron RBE value was highly variable in different sensitive target volumes and decreases with increasing sensitive target volumes. With 6-nm-diameter sensitive target as reference, RBE value was 1.77 for 6-nm diameter, 1.53 for 10 nm diameter with percentage difference 13%, and 1.40 for 15-nm diameter with percentage difference of 21%, respectively. The effect of different Geant4-DNA physical models on the RBE of low-energy electrons was small. Using the RBE value of 1.53 for physical model option2 as reference, the RBE values of option6 and option7 were 1.49 and 1.52, respectively, with the percentage differences of 2.6% and 0.6%, respectively.Conclusions:The RBE values of low energy electrons released by 157GdNCT in different sensitive target volumes and physical models were calculated by MKM to be 1.40-1.77.

Counting loss correction in ³⁷Ar activity measurement based on Geant4 simulation / 中国辐射卫生

@#<b>Objective</b> To correct the counting loss of ³⁷Ar below the activity threshold during the measurement of the absolute activity of the inert radioactive gas ³⁷Ar using the proportional counter filled with gas. <b>Methods</b> Monte Carlo simulation with Geant4 was performed to establish a proportional counter model and output the energy deposition spectrum of ³⁷Ar, which were used to simulate and analyze the causes and correction of counting loss. <b>Results</b> The photon detection efficiency was only 38.7% at 60 kPa. The counting loss was mainly caused by the wall effect produced by the photons, which could be reduced by increasing the gas pressure and corrected by extrapolation. The influence of wall effect at 100 kPa was 4.4%, and the deviation between simulation and experiment was < 0.6%. <b>Conclusion</b> A factor could be calculated by Geant4 simulation for the correction of counting loss, thus achieving the accurate measurement of ³⁷Ar activity by proportional counter.

Energy response and proton range measurement with EBT3 film simulated by Geant4 / 中国辐射卫生

@#<b>Objective</b> To calculate the energy dependence of absorbed dose in EBT3 film, and to reveal the error in the measurement of proton absorbed dose by EBT3 film. <b>Methods</b> Beam energy was gradually increased in the clinical photon and proton energy ranges. Geant4 was used to calculate the difference in absorbed dose between EBT3 film and the same volume of water. The results were compared with the theoretical values. <b>Results</b> For photons and protons, the thresholds for absorbed dose with energy dependence were 100 keV and 11 MeV, respectively. The energy dependence was consistent with the theoretical values when the photon and proton energies were higher than the corresponding thresholds, and irrelevant to the theoretical values when energies were lower than the thresholds. The differences between the proton Bragg peak and 50% dose point and the actual positions were less than 1%. <b>Conclusions</b> For protons and photons with high energy, the energy dependence of absorbed dose in EBT3 film is negligible. For protons and photons with low energy, EBT3 film shows very different energy dependence of absorbed dose, which should be taken into consideration. The proton Bragg peak and 50% dose point measured by EBT3 film are basically the same as the actual positions.

Effect of cavity under Bolus to shallow dose calculation precision of anisotropic analytical algorithm / 中国辐射卫生

Objective To research the effect of cavity under Bolus to anisotropic analytical algorithm (AAA) on calculation precision of dose in shallow tissue based on Monte Carlo method;Methods A 30 cm × 30 cm × 30 cm water phantom with the upper surface was constructed which was located at the source-axis distance (SAD) of the medical linear accelerator and the center as well as coincided with the central axis of the radiation field in Eclipse treatment panning system. Above the water phantom, a water film of 1 cm thick with or without different cavities was constructed or. AAA was used to calculate the dose distribution on the central axis and the x-axis of different depth of the water model with different cavities respectively. The accelerator model, the same water phantom and the water film were constructed and the dose distributions of the same positions were calculated with Geant4. Based on the Geant4 calculation result, the calculation precision of AAA with different cavity were compared;Results For cavities with area of 2 cm × 2 cm, if the thickness is smaller than 0.5 cm, the AAA calculation error is about 2%. with the cavity thickness increase, the AAA would overestimate the dose in the shallow area under the cavity. With the cavity area increase, the area where AAA overestimate the shallow dose gradually moved out until near the edge of the radiation field, and the calculation error on the central area gradually reduced until there is basically no error. Conclusions The shallow dose would be increased according to the cavity size when planning with AAA; If there are cavities with large volume, it is better to reposition.

Water-equivalence of ZrO2doped polystyrene by Monte Carlo simulation / 中华放射医学与防护杂志

Objective To design water-equivalent plastic scintillator detector for the measurement of absorbed dose in tumor radiotherapy.Methods The concentration of ZrO2to be doped in polystyrene was estimated according to the empirical formula,and then the Monte Carlo program Geant 4(GEometry And Tracking 4)was used to simulate the energy deposition and transport process of X-rays with different energies in water,solid water RW34(composed of 2.1 wt％TiO2doping polystyrene)and different concentrations of ZrO2particles doped in polystyrene.The dose and attenuation coefficients were compared among different materials at different depths of water.Results The doses at different depths and the attenuation coefficient of polystyrene(doped with about 0.4 wt％ZrO2nanoparticles)were much more consistent with those of water and even exhibit much better water-equivalence than RW34.Conclusions The simulation results provide the basis for the development of water-equivalent scintillator.

Comparisons of DNA damages in physics process caused by protons with different energies / 中华放射医学与防护杂志

Objective To compare the difference among DNA damages in physics processes caused by protons with different energies around Bragg peak.Methods By constructing the nucleus and DNA model using Geant4 and simulating the transportation processes of protons with different energies around Bragg peak in nucleus model based on Geant4-DNA,the information of interaction points were recorded.16％ of them were picked randomly to use as the points at which protons interact with DNA.After finding out the points which broke the DNA and writing their information to new files,these new files were treated with density-based spatial clustering of applications with noise (DBSCAN),so as to analyze and calculate the difference of DNA damages caused by protons with different energies.Results With the protons with energies from 20.0 to 0.6 MeV,the numbers of damage points and damage clusters increased from 49.86 to 549.88 and from 2.92 to 82.46,respectively;the numbers of clusters with different sizes had a remarkable increase,and the number of clusters with size not less than 5 increased by 400 times.The average cluster size increased slightly.Simple single strand breaks (SSSBs),complex single strand breaks (CSSBs),simple double strand breaks (SDSBs) and complex double strand breaks (CDSBs) of DNA increased by about 8,26,24 and 64 times,respectively.The proportion of single strand breaks (SSBs) decreased from 96.69％ to 89.37％,and the double strand breaks (DSBs) increased from 3.31％ to 10.63％.Conclusions The lower proton energy would result in the more complex damage to DNA and the harder repair of DNA damage.

Monte Carlo simulation and experimental investigation of 125I interseed dose attenuation / 中华放射医学与防护杂志

Objective To investigate the interseed dose attenuation for multiple 125I seeds.Methods Monte Carlo simulation was done by Geant 4 to investigate the dose distribution of single seed and multiple seeds.The results were compared with the dose calculation method from TG43-U1 and examined by experiments.Results The difference of single seed dose distribution between Monte Carlo method and line source model was ± 3％.The difference between Monte Carlo method and experiment result was ± 5％.The interseed dose attenuation of multiple seeds at the interesting points was 3.8％ to 13.2％ and the average interseed dose attenuation was 7.2％.The difference of experiment result and Monte Carlo result was less than 6％.Conclusions The interseed attenuation is about 7％ and the maximum value may be larger than 13％ for multiple seeds.The interseed dose attenuation may be larger in tissue.So it is not accurate to calculate the dose distribution by using TG43-U1.

Simulação e análise dosimétrica de protonterapia e íons de carbono no tratamento do melanoma uveal / Simulation and dosimetric analysis of proton and carbon ion therapy in the treatment of uveal melanoma

OBJETIVO: Este artigo apresenta a avaliação dosimétrica da radioterapia por íons de carbono em comparação à protonterapia. MATERIAIS E MÉTODOS: As simulações computacionais foram elaboradas no código Geant4 (GEometry ANd Tracking). Um modelo de olho discretizado em voxels implementado no sistema Siscodes (sistema computacional para dosimetria em radioterapia) foi empregado, em que perfis de dose em profundidade e curvas de isodose foram gerados e superpostos. Nas simulações com feixe de íons de carbono, distintos valores de energia do feixe foram adotados, enquanto nas simulações com feixe de prótons os dispositivos da linha de irradiação foram incluídos e diferentes espessuras do material absorvedor foram aplicadas. RESULTADOS: As saídas das simulações foram processadas e integradas ao Siscodes para gerar as distribuições espaciais de dose no modelo ocular, considerando alterações do posicionamento de entrada do feixe. Os percentuais de dose foram normalizados em função da dose máxima para um feixe em posição de entrada específica, energia da partícula incidente e número de íons de carbono e de prótons incidentes. CONCLUSÃO: Os benefícios descritos e os resultados apresentados contribuem para o desenvolvimento das aplicações clínicas e das pesquisas em radioterapia ocular por íons de carbono e prótons.

OBJECTIVE: The present paper addresses the dosimetric evaluation of carbon ion radiotherapy as compared with proton therapy. MATERIALS AND METHODS: Computer simulations were undertaken with the Geant4 (GEometry ANd Tracking) code. An eye model discretized into voxels and implemented in the Siscodes system (computer system for dosimetry in radiation therapy) was utilized to generate and superimpose depth dose profiles and isodose curves. Different values for beam energy were adopted in the simulations of carbon ion beams, while in the simulation with proton beams irradiation line devices were included with different absorbing material thicknesses. RESULTS: The simulations outputs were processed and integrated into the Siscodes to generate the spatial dose distribution in the eye model, considering changes in the beam entrance position. The dose rates were normalized as a function of the maximum dose for a beam at a specific entrance position, incident particle energy and number of incident carbon ions and protons. CONCLUSION: The described benefits together with the presented results contribute to the development of clinical applications and researches on carbon ion and proton therapy.

Study on the 6 MV Photon Beam Characteristics and Analysis Method from Medical Linear Accelerators Using Geant4 Medical Linac2 Example / 의학물리

In this study, Geant4 based Monte Carlo simulations were carried out for medical linear accelerator. Modified Medical Linac2 toolkit was used for calculation. The energy spectrum, most probable energy and the photon mean energy compared with the published results using the EGS4 code. The results well agreed with published results. The calculated results of photon fluence, energy fluence and mean energy according to the radius from the centre of the beam were analyzed. Monte Carlo simulation using Medical Linac2 code is considered to be useful for analysis of medical linear accelerator. Because the calculated results varies depending on Physics List model for same head structure. It it important to choose the right model for research purpose. Monte Carlo simulation using GEANT4 Medical Linac2 is a valuable for any novice to adopt this code to the study related to 6 MV photon fluence from medical linear accelerator.

Calculation of Energy Spectra for Electron Beam of Medical Linear Accelerator Using GEANT4 / 의학물리

The energy spectra for electron beam of medical linear accelerator were calculated using a GEANT4 Medical Linac 2 example code. The incident electron mean energy were 6, 9, 12, 16, 20 MeV. This code was designed to calculate electron beam energy spectra according to material, thickness and location of electron scattering foil affecting electron beam characteristic. Lead, Copper, Aluminum and Gold were used for scattering foil. The energy distribution for electron and photon were analyzed by changing position of scattering foil in the head of linear accelerator. The effect of electron scattering foil on energy spectra which is basic data of simulation for medical linear accelerator were presented. The calculated results would be used in design of medical accelerator head.

Estudo comparativo de dosimetria computacional entre modelos homogêneos e um modelo voxel em mamografia: uma discussão de aplicações em testes de constância e cálculo de dose glandular em pacientes / Comparative study of computational dosimetry involving homogeneous phantoms and a voxel phantom in mammography: a discussion on applications in constancy tests and calculation of glandular dose in patients

OBJETIVO: Comparar dados de dosimetria e fluência de fótons entre diferentes modelos de mama, discutindo as aplicações em testes de constância e estudos dosimétricos aplicados à mamografia. MATERIAIS E MÉTODOS: Foram simulados diferentes modelos homogêneos e um modelo antropomórfico de mama tipo voxel, sendo contabilizadas: a dose total absorvida no modelo, a dose absorvida pelo tecido glandular/material equivalente, e a dose absorvida e a fluência de fótons em diferentes profundidades dos modelos. Uma câmara de ionização simulada coletou o kerma de entrada na pele. As combinações alvo-filtro estudadas foram Mo-30Mo e Mo-25Rh, para diferentes potenciais aceleradores de 26 kVp até 34 kVp. RESULTADOS: A dose glandular normalizada, comparada ao modelo voxel, resultou em diferenças entre -15 por cento até -21 por cento para RMI, -10 por cento para PhantomMama e 10 por cento para os modelos Barts e Keithley. A variação dos valores da camada semirredutora entre modelos foi geralmente inferior a 10 por cento para todos os volumes sensíveis. CONCLUSÃO: Para avaliar a dose glandular normalizada e a dose glandular, em mamas médias, recomenda-se o modelo de Dance. Os modelos homogêneos devem ser utilizados para realizar testes de constância em dosimetria, mas eles não são indicados para estimar a dosimetria em pacientes reais.

OBJECTIVE: To compare data regarding dosimetry and photons fluence in different breast phantoms, discussing constancy tests and dosimetry applied to mammography. MATERIALS AND METHODS: Different homogeneous breast phantoms and one anthropomorphic voxel phantom were developed for collection of data regarding total absorbed dose in the phantom, absorbed dose in the glandular tissue material-equivalent, absorbed dose and photons fluence at different depths in the phantoms. A simulated ionization chamber collected the entrance skin kerma. Target-filter combinations (Mo-30Mo and Mo-25Rh) were studied for different accelerating potentials of 26 kVp to 34 kVp. RESULTS: As compared with the voxel phantom, the normalized glandular dose resulted in differences from -15 percent to -21 percent for RMI, -10 percent for PhantomMama, and 10 percent for the Barts and Keithley models. The half-value layer variation was generally < 10 percent for all the sensitive volumes. CONCLUSION: The phantom proposed by Dance is recommended for evaluating the glandular dose and normalized glandular dose in a standard breast. Homogeneous phantoms should be utilized for constancy tests in dosimetry, but they are not appropriate for estimating dosimetry in actual patients.

Análise da distribuição espacial de dose absorvida em próton terapia ocular / Spatial distribution analysis of absorbed dose in ocular proton radiation therapy

OBJETIVO: Propõe-se avaliar os perfis de dose em profundidade e as distribuições espaciais de dose para protocolos de radioterapia ocular por prótons, a partir de simulações computacionais em código nuclear e modelo de olho discretizado em voxels. MATERIAIS E MÉTODOS: As ferramentas computacionais empregadas foram o código Geant4 (GEometry ANd Tracking) Toolkit e o SISCODES (Sistema Computacional para Dosimetria em Radioterapia). O Geant4 é um pacote de software livre, utilizado para simular a passagem de partículas nucleares com carga elétrica através da matéria, pelo método de Monte Carlo. Foram executadas simulações computacionais reprodutivas de radioterapia por próton baseada em instalações pré-existentes. RESULTADOS: Os dados das simulações foram integrados ao modelo de olho através do código SISCODES, para geração das distribuições espaciais de doses. Perfis de dose em profundidade reproduzindo o pico de Bragg puro e modulado são apresentados. Importantes aspectos do planejamento radioterápico com prótons são abordados, como material absorvedor, modulação, dimensões do colimador, energia incidente do próton e produção de isodoses. CONCLUSÃO: Conclui-se que a terapia por prótons, quando adequadamente modulada e direcionada, pode reproduzir condições ideais de deposição de dose em neoplasias oculares.

OBJECTIVE: The present study proposes the evaluation of the depth-dose profiles and the spatial distribution of radiation dose for ocular proton beam radiotherapy protocols, based on computer simulations in nuclear codes and an eye model discretized into voxels. MATERIALS AND METHODS: The employed computational tools were Geant4 (GEometry ANd Tracking) Toolkit and SISCODES (Sistema Computacional para Dosimetria em Radioterapia - Computer System for Dosimetry in Radiotherapy). Geant4 is a toolkit for simulating the passage of particles through the matter, based on Monte Carlo method. Computer simulations of proton therapy were performed based on preexisting facilities. RESULTS: Simulation data were integrated into SISCODES on the eye's model generating spatial dose distributions. Dose depth profiles reproducing the pure and modulated Bragg peaks are presented. Relevant aspects of proton beam radiotherapy planning are considered such as material absorber, modulation, collimator dimensions, incident proton energy and isodose generation. CONCLUSION: The conclusion is that proton therapy when properly modulated and directed can reproduce the ideal conditions for the dose deposition in the treatment of ocular tumors.

Estudo dosimétrico para caracterização de um Sistema postal de controle de qualidade em braquiterapia

A Braquiterapia é uma etapa essencial do tratamento de vários tipos de câncer. O uso de fontes de 192Ir com alta taxa de dose impõe a necessidade de procedimentos apropriados de calibração e controle da qualidade, de forma a garantir a exatidão da dose administrada. Um programa em GEANT4 foi desenvolvido para calcular grandezas dosimétricas em um fantoma de acrílico. Assim foi possível definir uma metodologia para avaliar a dose na vizinhança de uma fonte de braquiterapia utilizando um formalismo em função da grandeza dose absorvida na água para dosimetria termoluminescente. Um fantoma de acrlílico foi proposto e caracterizado com grandezas do protocolo TG- 3 calculadas pelo método de Monte Carlo. O fantoma foi irradiado com os TLDs no equipamento de braquiterapia do Varian Gammamed Plus, a dose e o kerma de referência calculado concordaram em 0,30%.

High dose rate Brachytherapy is an essential part of the treatment of several types of cancer. The use of high dose rate 192Ir sources requires appropriate calibration in order to ensure the desired level of accuracy of the dose delivered. A GEANT4 program was developed to calculate dosimetric quantities in an acrylic phantom. Thus it was possible to define a methodology for calculating the dose around a brachytherapy source using a termoluminescent dosimetry formalism in terms of water absorbed dose. An acrylic phantom was proposed and characterized with magnitudes protocol TG-43 calculated by Monte Carlo method. The phantom was irradiated in Varian's brachytherapy equipment Gammamed Plus, the dose and the kerma calculated reference agreed at 0,30%.

Monte Carlo Study Using GEANT4 of Cyberknife Stereotactic Radiosurgery System / 의학물리

Cyberknife with small field size is more difficult and complex for dosimetry compared with conventional radiotherapy due to electronic disequilibrium, steep dose gradients and spectrum change of photons and electrons. The purpose of this study demonstrate the usefulness of Geant4 as verification tool of measurement dose for delivering accurate dose by comparing measurement data using the diode detector with results by Geant4 simulation. The development of Monte Carlo Model for Cyberknife was done through the two-step process. In the first step, the treatment head was simulated and Bremsstrahlung spectrum was calculated. Secondly, percent depth dose (PDD) was calculated for six cones with different size, i.e., 5 mm, 10 mm, 20 mm, 30 mm, 50 mm and 60 mm in the model of water phantom. The relative output factor was calculated about 12 fields from 5 mm to 60 mm and then it compared with measurement data by the diode detector. The beam profiles and depth profiles were calculated about different six cones and about each depth of 1.5 cm, 10 cm and 20 cm, respectively. The results about PDD were shown the error the less than 2% which means acceptable in clinical setting. For comparison of relative output factors, the difference was less than 3% in the cones lager than 7.5 mm. However, there was the difference of 6.91% in the 5 mm cone. Although beam profiles were shown the difference less than 2% in the cones larger than 20 mm, there was the error less than 3.5% in the cones smaller than 20 mm. From results, we could demonstrate the usefulness of Geant4 as dose verification tool.

Evaluation of the Secondary Particle Effect in Inhomogeneous Media for Proton Therapy Using Geant4 Based MC Simulation / 의학물리

In proton therapy, the analysis of secondary particles is important due to delivered dose outside the target volume and thus increased potential risk for the development of secondary cancer. The purpose of this study is to analyze the influence of secondary particles from proton beams on fluence and energy deposition in the presence of inhomogeneous material by using Geant4 simulation toolkit. The inhomogeneity was modeled with the condition that the adipose tissue, bone and lung equivalent slab with thickness of 2 cm were inserted at 30% (Plateau region) and 80% (Bragg peak region) dose points of maximum dose in Bragg curve. The energy of proton was varied with 100, 130, 160 and 190 MeV for energy dependency. The results for secondary particles were presented for the fluence and deposited energy of secondary particles at inhomogeneous condition. Our study demonstrates that the fluence of secondary particles is neither influenced insertion of inhomogeneties nor the energy of initial proton, while there is a little effect by material density. The deposited energy of secondary particles has a difference in the position placed inhomogeneous materials. In the Plateau region, deposited energy of secondary particles mostly depends on the density of inserted materials. Deposited energy in the Bragg region, in otherwise, is influenced by both density of inserted material and initial energy of proton beams. Our results suggest a possibility of prediction about the distribution of secondary particles within complex heterogeneity.

Precision Validation of Electromagnetic Physics in Geant4 Simulation for Proton Therapy / 의학물리

Geant4 (GEometry ANd Tracking) provides various packages specialized in modeling electromagnetic interactions. The validation of Geant4 physics models is a significant issue for the applications of Geant4 based simulation in medical physics. The purpose of this study is to evaluate accuracy of Geant4 electromagnetic physics for proton therapy. The validation was performed both the Continuous slowing down approximation (CSDA) range and the stopping power. In each test, the reliability of the electromagnetic models in a selected group of materials was evaluated such as water, bone, adipose tissue and various atomic elements. Results of Geant4 simulation were compared with the National Institute of Standards and Technology (NIST) reference data. As results of comparison about water, bone and adipose tissue, average percent difference of CSDA range were presented 1.0%, 1.4% and 1.4%, respectively. Average percent difference of stopping power were presented 0.7%, 1.0% and 1.3%, respectively. The data were analyzed through the kolmogorov-smirnov Goodness-of-Fit statistical analysis test. All the results from electromagnetic models showed a good agreement with the reference data, where all the corresponding p-values are higher than the confidence level alpha=0.05 set.

Preliminary Study on Performance Evaluation of a Stacking-structure Compton Camera by Using Compton Imaging Simulator / 의학물리

A Compton camera, which is based on the geometrical interpretation of Compton scattering, is a very promising gamma-ray imaging device considering its several advantages over the conventional gamma-ray imaging devices: high imaging sensitivity, 3-D imaging capability from a fixed position, multi-tracing functionality, and almost no limitation in photon energy. In the present study, a Monte Carlo-based, user-friendly Compton imaging simulator was developed in the form of a graphical user interface (GUI) based on Geant4 and MATLAB (TM). The simulator was tested against the experimental result of the double-scattering Compton camera, which is under development at Hanyang University in Korea. The imaging resolution of the simulated Compton image well agreed with that of the measured image. The imaging sensitivity of the measured data was 2~3 times higher than that of the simulated data, which is due to the fact that the measured data contains the random coincidence events. The performance of a stacking-structure type Compton camera was evaluated by using the simulator. The result shows that the Compton camera shows its highest performance when it uses 4 layers of scatterer detectors.

Estimates of Space Radiation Exposure to Astronauts Using Male Voxel Model Based on MRI / 航天医学与医学工程

Objective To predict the astronaut organs radiation exposure and related health risks in the space radiation environment, the calculated method is studied. Methods A male voxel human model based on MRI and radiation data bank was build. The calculation was carried out with Monte Carlo particle transporting program GEANT4. Results The organ absorbed dose distribution and the effec-tive doses to the model in isotropic proton fields with energies ranges from 10 MeV to 500 MeV were obtained. Conclusion Based on the Chinese astronaut voxel model and the data set of proton spectrum measured in the space cabin, the cumulated dose in the model is gotten. The calculated skin dose is about 148.6 μGy/d, which is within in the range of 100 -300 μGy/d, published by USA and Russia.

(99m)Tc Generator Safety Simulation Based on GEANT4 / 의학물리

Technisium ((99m)Tc) is one of the most widely used radioactive isotopes for diagnosis in nuclear medicine. In general, technisium is produced inside the so called (99m)Tc generator which is usually made out of lead to shield relatively high energy radiation from (99)Mo and its daughter nuclide (99m)Tc. In this paper, a GEANT4 simulation is carried out to test the safety of the (99m)Tc generator, taking the Daiichi product with radioactivity of 500 mCi as an example. According to the domestic regulation on radiation safety, the dose at 10 cm and 100 cm away from the surface of shielding container should not exceed 2.0 mSv/h and 0.02 mSv/h, respectively. The simulated dose turned out to be less than the limit, satisfying the domestic regulation.

A Monte Carlo Simulation Study of a Therapeutic Proton Beam Delivery System Using the Geant4 Code / 의학물리

We studied a Monte Carlo simulation of the proton beam delivery system at the National Cancer Center (NCC) using the Geant4 Monte Carlo toolkit and tested its feasibility as a dose verification framework. The Monte Carlo technique for dose calculation methodology has been recognized as the most accurate way for understanding the dose distribution in given materials. In order to take advantage of this methodology for application to externalbeam radiotherapy, a precise modeling of the nozzle elements along with the beam delivery path and correct initial beam characteristics are mandatory. Among three different treatment modes, double/single.scattering, uniform scanning and pencil beam scanning, we have modeled and simulated the double.scattering mode for the nozzle elements, including all components and varying the time and space with the Geant4.8.2 Monte Carlo code. We have obtained simulation data that showed an excellent correlation to the measured dose distributions at a specific treatment depth. We successfully set up the Monte Carlo simulation platform for the NCC proton therapy facility. It can be adapted to the precise dosimetry for therapeutic proton beam use at the NCC. Additional Monte Carlo work for the full proton beam energy range can be performed.