geant4 code

Scattering factor (Scp) is one of the important factors in the dosimetry of medical accelerators. Variation of scattering factor is one of the factors that affect the dose received by the patient. In this research is tried to simulate the geometry of the compact model linear accelerator using Geant4 code and the appropriate phase space of this accelerator has been extracted using electron source data. Phase space are required to increase the accuracy in Monte Carlo calculations. Phase space data include the gamma rays energy and angular spectrum that generated by the 6 MeV electrons with 0.07 FWHM. Comparison between simulated and practical values of SCP ​​shows that the introduced phase space is a suitable source for dosimetric calculations of compact linear accelerometer.

In this study, a Compton camera imaging system containing several scatterer layers made of Si and a LYSO detector as an absorber layer were designed and simulated using Geant4 code. At first, the efficiency of the system according to the number of scatterer layers was optimized using a gamma point source with various energies. After finding the best structure of the system which contains 10 layers of scatterer, two similar setup of Compton camera were placed perpendicularly to the proton beam around the phantom to take image of the position of the prompt gamma emission resulted from the nuclear interaction of the proton beam with the phantom. In order to imaging the gammas, information such as interaction positions and deposited energies in the scatterers and absorber were recorded by Geant4 code in a root file. Then, using a Compton camera reconstruction algorithm, production position profile of gammas was reconstructed in a MATLAB software. A Comparison of the gamma photon distribution and dose distribution showes that this Compton camera structure is able to measure the proton beam range with less than 7 mm error, which proves the capability of prompt gammas detection for verification of the proton beam range during proton therapy.

In radiation therapy, ions heavier than proton have more biological advantages than a proton beam. Recently, ion helium has been considered due to high linear energy transfer (LET) to the medium and a higher relative biological effect (RBE). To design the spread-out Bragg peak (SOBP) of biological dose for radiation with any type of ion, we need exact values of RBE, which is dependent to dose, LET, and tissue specific parameter, and has spatial variations relative to depth in the tissue. Here, we calculate the exact value of RBE in helium ion irradiating V79 cell line by applying a parametric expression for RBE variations relative to LET, as well as using the Monte Carlo simulation code Geant4 to calculate the LET and the dose profile. The profiles of the Bragg Peak and LETs are calculated for each slice in the tumor region. To generate an appropriate biological SOBP, we compute a set of weighting factors using matrix computations, and by modulating helium ion beams, creation of optimal homogeneity at SOBP for biological doses was done.

Imaging and identifying materials with high atomic numbers and densities, especially radioactive materials, is one of the issues that have been especially considered in recent years. Due to some limitations in conventional and old imaging techniques, finding an alternative method is very important. The cosmic muons with an infinite source are one of the sources that have been recently studied for heavy objects imaging, and the major efforts in this field have focused on increasing the accuracy and efficiency of muon radiography systems. Use of plastic scintillator improves the accuracy and reduces the cost of muon radiography. In recent decades, different methods have been proposed for the use of these scintillators in development of muon radiography systems. Since the basis of the work of radiography systems is the spatial resolution of the detector, any study that can increase the accuracy of a muon detection system will ultimately improve the quality of muon radiography system. In this study, using a special configuration of plastic scintillators and photomultiplier tubes, the resolution of the muon location identification on the detector plate is optimized. The simulations performed by Geant4 code for different states, show that the final resolution of the detector plates is about 1 cm and, in terms of the resolution of detection, the best scintillator available for the proposed system is BC-408. In addition, among the examined photomultiplier tube layouts, the most accurate configuration is square alignment with uniform distances and the most suitable angle of positioning of the plates relative to the horizons is 10 degrees.

In this paper, cellular S-values for monoenergetic electron sources with energy from 1 to 70keV and the Auger-electron emitting radionuclides Tc-99m and In-111 were calculated in liquid water using the Geant4 Monte Carlo toolkit with the low energy extension Geant4-DNA. The results were compared to corresponding MIRD database and the differences were calculated. Differences between Geant4-DNA and MIRD results up to 70% were found; However, for the present monoenergetic sources and radionuclides, they mostly remain below 20%. Calculated S-values in this paper, were in good agreement to S-values obtained in the other literatures. This study is an important step for performing cellular dosimetry which the results would improve the treatment planning in the country.

Brachytherapy is a therapeutic approach in which radioactive sources are used to irradiate malignant tumors from near distance. In this study, the comparison of dose distribution in iodine-125 source, STM 1251 and Oncoseed 6711 models was performed using the Monte Carlo Geant4 code. The results obtained from the Monte Carlo calculations have been compared with the TG43U1 formulation and also with the available experimental results. According to the TG43U1 formula, the dose distribution of the STM 1251 has a greater influence than Oncoseed 6711. Also, this trend was observed in the region near the phantom surface that was not balanced with radiation distribution conditions. In this region, there was no significant difference between TG43U1 protocol and experimental values ​​and calculated results in this study. Therefore, the selection of the source model can be done based on the results of the Geant4 code.

For their appropriate temporal resolution، scintillator detectors are used in the Alborz observatory. In this work، the behavior of the scintillation detectors for the passage of electrons with different energies and directions were studied using the simulation code GEANT4. Pulse shapes of scintillation light، and such characteristics as the total number of photons، the rise time and the falling time for the optical pulses were computed for the passage of electrons with energies of 10، 100 and 1000 MeV. Variations of the characteristics of optical pulse of scintillation with incident angle and the location of electrons were also investigated

One of the most important measures of therapeutic quality in Microbeam Radiation Therapy (MRT) is the Peak to Valley Dose Ratio (PVDR). This parameter is a criterion to evaluate ablation of cancerous cells and sparing of normal cells in tumor and in its surrounding region. The aim of this work is to study the influence of using gold and gadolinium nano-particles as contrast agents on dose distribution and PVDR when a phantom is irradiated by a typical micro-planar X-ray beam of European Synchrotron Radiation Facility (ESRF3). Using Geant4 computer code, a model has been designed to simulate depth dose in an intact phantom made of PMMA4 and dose distribution in a phantom containing assumed tumors in therapeutic techniques of MIMRT5 and BIMRT6. Comparison of simulated results in the intact phantom with the measured values of depth dose reveals the validity of our simulation with the designed model. To improve the efficiency of MRT, enhancement of absorbed dose in tumor tissues and sparing of normal tissues due to presence of contrast agents have been studied. The obtained results show that the enhancement is more noticeable for Au at the peak region and for Gd in the valley region. This approach of introducing contrast agents in MRT could hopefully prepare new treatment planning and improves the efficiency of tumor therapy.