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The importance of water shortage in arid and semi-arid regions is more evident due to the limitation of water resources, and the preparation of water resources is necessary to protect and reduce the vulnerability of these resources. Therefore, in this study, considering the vulnerability of water and soil resources in arid and semiarid regions and the geographical structure of Zagros inland basins, the Izadkhast plain from the south of Fars province was selected to investigate the vulnerability of water resources. For this purpose, six parameters of water depth, net feed, aquifer environment, soil texture, topography, and hydraulic conductivity of the aquifer were analyzed using the DRASTIC model. The results showed that almost 50% of the plains were in the high vulnerability class, and 28% were in the very high vulnerability class. In the east and center of the plain, places with high vulnerability to pollutants and contaminated water were found. The effect of the formations in the east of the basin can be seen because, at the outlet of the rivers in the east of the basin, the amount of sulfate has increased dramatically, which indicates the presence of evaporate formations with gypsum. In the center of the basin, the heavy texture of the soil, the low slope, and the accumulation of most of the water entering the basin, some of which have a lot of salts, have increased the vulnerability of this part. Another result of this study is that the DRASTIC model has high efficiency in evaluating vulnerabilities similar to this research. [ABSTRACT FROM AUTHOR]

Floods are occurring as an environmental hazard in many parts of the world, especially in countries that have been ineffective in crisis management and resource conservation. This natural hazard has become one of the most damaging natural disasters since the reckless activities of human beings in exploiting the natural environment have increased. One of the ways to deal with this danger is to predict the occurrence of floods. The models that are used to predict the occurrence of floods may not have the same accuracy in predicting precipitation events in different seasons of the year. Due to the importance of this issue, in this study, the results of the the Geomorphological Instantaneous Unit Hydrograph (GIUH) model in predicting floods in winter and spring in Minab catchment (Brentin) were compared. The data include the maximum hourly flow and their corresponding precipitation for three spring and three winter events. First, the required parameters of GIUH model including branching ratio, length ratio and area ratio for the basin were estimated using GIS softwar. Then, the events of winter and spring seasons, the peak discharge values, and the time of the peak discharge were compared. The results of this comparison showed that GIUH model predicts peak discharge and peak flood time occurring in winter (with average values of 20.09 and 45.64%, respectively). It is less distant from the observed data, and has a higher accuracy than spring events (with average values of 57.3 and 119.7, respectively). [ABSTRACT FROM AUTHOR]

Exposure to radiation is one of the main sources of risk to staff employed in reactor facilities. The staff of a tokamak is exposed to a wide range of neutrons and photons around the tokamak hall. The International Thermonuclear Experimental Reactor (ITER) is a nuclear fusion engineering project and the most advanced experimental tokamak in the world. From the radiobiological point of view, ITER dose rates assessment is particularly important. The aim of this study is the assessment of the amount of radiation in ITER during its normal operation in a radial direction from the plasma chamber to the tokamak hall. To achieve this goal, the ITER system and its components were simulated by the Monte Carlo method using the MCNPX 2.6.0 code. Furthermore, the equivalent dose rates of some radiosensitive organs of the human body were calculated by using the medical internal radiation dose phantom. Our study is based on the deuterium-tritium plasma burning by 14.1 MeV neutron production and also photon radiation due to neutron activation. As our results show, the total equivalent dose rate on the outside of the bioshield wall of the tokamak hall is about 1 mSv per year, which is less than the annual occupational dose rate limit during the normal operation of ITER. Also, equivalent dose rates of radiosensitive organs have shown that the maximum dose rate belongs to the kidney. The data may help calculate how long the staff can stay in such an environment, before the equivalent dose rates reach the whole-body dose limits.

Understanding the morphodynamics of river junctions is an important part of fluvial geomorphological studies that were provided suitable conditions to measure erosion and sediment changes at the junction of Dinver and Gamasiab rivers by the occurrence of floods in April 2019. Due to the complexity, 3D numerical simulation is not cost-effective, and onedimensional models, also, have some errors. For this reason, the use of two-dimensional models can be useful. Therefore, the SRH-2D model was used to investigate the effect of the flood on the morphology of the confluence of the Dinver River to Gamasiab. To study the morphological changes in the study area, elevation position and topography was mapped in two stages before and after the flood and also a granulometric experiment was performed. Due to the fact that the SRH_2D model does not have the ability to network, the required mesh was prepared using SMS software and the output file of the model was saved in TECPLOT format. The results showed that in a flood with a 35-year return period of the Dinver River to Gamasiab junction, with a meander- meander junction at a 40-degree angle, bed erosion in the downstream part of the junction begins to occur early in the onset of flooding and gradually expands to the upstream. However, sedimentation occurs shortly after the peak of the flood in the stagnation zone and then growing the spurs as the flood decreases, and developing the outer arch of the Gamasiab River as at the flood goes to end. [ABSTRACT FROM AUTHOR]

Introduction: Grid therapy recently has been picking momentum due to favorable outcomes in bulky tumors. This is being termed as Spatially Fractionated Radiation Therapy (SFRT) and lattice therapy. SFRT can be performed with specially designed blocks made with brass or cerrobend with repeated holes or using multi - leaf collimators. Aim: The main challenge is the mystery behind the lower PDD (percentage depth dose) in grid fields. The knowledge about the beam quality, indexed by TPR20/10 (Tissue Phantom Ratio), is also necessary for absolute dosimetry of grid fields. Since the grid may change the quality of the primary photons, a new k_ (q,q_0)should be requested for absolute dosimetry of grid fields. The present Monte Carlo (MC) study was devoted to resolving the questions. Methods: In this study, the main components of a typical medical linac in 6 MV mode were considered to be simulated using MCNPX® code. Additionally, a commercial grid therapy device was used to simulate the grid fields. After validation of the MC model, output factor, depth of maximum dose, PDDs, dose profiles, TPR20/10, electron and photon spectra were compared between open and grid fields. Results: The results demonstrated that output factors for grid fields are 0.2 ± 0.05 lower than in open fields. The dmax is the same for open and grid fields. The difference in TPR20/10 of open and grid fields is observable (~5%). Conclusions: TPR20/10 is still a good index for the beam quality in grid fields and consequently choose the correct k (q, q_0) in measurements. The lower depth dose (~10%) in grid therapy is due to lower depth fluence with scatter radiation but it does not impact the dosimetry as the calibration parameters are insensitive to the effective beam energies. Standard dosimetry in open beam based on international protocol could be used. [ABSTRACT FROM AUTHOR]

169Yb has been recently used as an HDR brachytherapy source for cancer treatment. In this paper, dosimetric parameters of a new design of 169Yb HDR brachytherapy source were determined by Monte Carlo (MC) method and film dosimetry. In this new source, the radioactive core has been encapsulated twice for safety purposes. The calculations of dosimetric parameters carried out using MC simulation in water and air phantom. In order to exclude photon contamination's cutoff energy, δ was set at 10 keV. TG‐43U1 data dosimetric, including Sk, Λ, g(r), F(r, θ) was computed using outputs from the simulation and their statistical uncertainties were calculated. Dose distribution around the new prototype source in PMMA phantom in the framework of AAPM TG‐43 and TG‐55 recommendations was measured by Radiochromic film (RCF) Gafchromic EBT3. Obtained air kerma strength, Sk, and the dose rate constant, Λ, from simulation has a value of 1.03U ± 0.03 and 1.21 cGyh−1U−1 ± 0.03, respectively. The radial dose function was calculated at radial distances between 0.5 and 10 cm with a maximum value of 1.15 ± 0.03 at 5–6 cm distances. The anisotropy functions for radial distances of 0.5–7 cm and angle distances 0° to180° were calculated. The dosimetric data of the new HDR 169Yb source were compared with another reference source of 169Yb‐HDR and were found that has acceptable compatibility. In addition, the anisotropy function of the MC simulation and film dosimetry method at a distance of 1 cm from this source was obtained and a good agreement was found between the anisotropy results. [ABSTRACT FROM AUTHOR]

Byline: Iraj. Jabbari, Shahram. Monadi A Monte Carlo treatment plan verification (MCTPV) system was developed for clinical treatment plan verification (TPV), especially for the conformal and intensity-modulated radiotherapy (IMRT) plans. [...]

Background: In the past, GRID therapy was used as a treatment modality for the treatment of bulky and deeply seated tumors with orthovoltage beams. Now and with the introduction of megavoltage beams to radiotherapy, some of the radiotherapy institutes use GRID therapy with megavoltage photons for the palliative treatment of bulky tumors. Since GRID can be a barrier for weakening the photoneutrons produced in the head of medical linear accelerators (LINAC), as well as a secondary source for producing photoneutrons, therefore, in terms of radiation protection, it is important to evaluate the GRID effect on photoneutron dose to the patients. Methods: In this study, using the Monte Carlo code MCNPX, a full model of a LINAC was simulated and verified. The neutron source strength of the LINAC (Q), the distributions of flux (φ), and ambient dose equivalent (H*[10]) of neutrons were calculated on the treatment table in both cases of with/without the GRID. Finally, absorbed dose and dose equivalent of neutrons in some of the tissues/organs of MIRD phantom were computed with/without the GRID. Results: Our results indicate that the GRID increases the production of the photoneutrons in the LINAC head only by 0.3%. The calculations in the MIRD phantom show that neutron dose in the organs/tissues covered by the GRID is on average by 48% lower than conventional radiotherapy. In addition, in the uncovered organs (by the GRID), this amount is reduced to 25%. Conclusion: Based on the findings of this study, in GRID therapy technique compared to conventional radiotherapy, the neutron dose in the tissues/organs of the body is dramatically reduced. Therefore, there will be no concern about the GRID effect on the increase of unwanted neutron dose, and consequently the risk of secondary cancer. [ABSTRACT FROM AUTHOR]

Introduction: Crosstalk is a leakage of X-ray or light produced in a matrix of X-ray detectors or array of photodiodes in one element to other elements affecting on image contrast and spatial resolution. In this study, we assessed X-ray crosstalk in a computed tomography (CT) scanner with small detector elements to estimate the effect of various parameters such as X-ray tube voltage, detector element sizes, scintillator material, impurities in the scintillator material, and the material of detector separators on X-ray crosstalk. Materials and Methods: This study was performed using Monte Carlo simulation. In the first step, X-ray tube and its energy spectrum at the energies of 80, 100, 120, and 140 keV were simulated and validated by using SpekCalc and t-test. Then, other important parts of CT scanner, namely filters, detectors, and grids were simulated. X-ray crosstalk between CT detectors was calculated in air and in the presence of water phantom (as a simulator of human body) to compare the effect of scattered photons. Finally, the influence of some important parameters on X-ray crosstalk was evaluated. Results: In CT scanner with small elements, when using phantom, crosstalk increases by 16-50%. Using the lowest possible energies of X-ray, decreases the crosstalk up to 43% of its initial amount. Furthermore coating a 10 or 20 μm layer of tungsten or lead on the detector separators, decreases the X-ray crosstalk significantly. Conclusion: Choosing the proper high voltage, detectors' material and its dimensions, scintillator impurities and septa material can decrease X-ray crosstalk. [ABSTRACT FROM AUTHOR]

Introduction: Tumor volume delineation is the most important step in the radiation treatment planning. In this study the impact of PET/CT data on the tumor delineation precision of non-small cell lung cancer (NSCLC) was investigated. Methods: PET/CT images of 20 patients with primary NSCLC were obtained and imported to the treatment planning system for image fusion, contouring and radiation treatment planning. For each patient two separate gross tumor volumes were delineated based on CT and PET/CT images as GTVCT and GTVPET/CT, respectively. In addition, three different indices including conformity index (CI), geographic miss index (GMI) and geographic include index (GII) were calculated to quantify the match and mismatches degree between derived volumes. Then, for each patient an appropriate 3D conformal treatment plan was made based on the PTVCT and then these plans were applied on the PTVPET/CT. Afterwards, the dose coverage of PTVPET/CT was estimated through several dosimetric parameters. Results: The GTVPET/CT was larger than GTVCT for majority of cases. The 25% exceeded volumetric alterations were observed in 8 of all cases (40%). Mean values of CI, GMI and GII were 0.43, 0.42 and 0.34, respectively. Also, dosimetric parameters indicated inadequate dose coverage of PTVPET/CT in CT-based RT plans for most of the patients. Conclusion: Incorporating PET data into tumor delineation process had a great potential to improve the quality of radiation treatment planning for NSCLC. [ABSTRACT FROM AUTHOR]

High-dose-rate (HDR) brachytherapy is a common method for cancer treatment in clinical brachytherapy. Because of the different source designs, there is a need for specific dosimetry data set for each HDR model. The purpose of this study is to obtain detailed dose rate distributions in water phantom for a first prototype HDR Ir brachytherapy source model, IRAsource, and compare with the other published works. In this study, Monte Carlo N-particle (MCNP version 4C) code was used to simulate the dose rate distributions around the HDR source. A full set of dosimetry parameters reported by the American Association of Physicists in Medicine Task Group No. 43U1 was evaluated. Also, the absorbed dose rate distributions in water, were obtained in an along-away look-up table. The dose rate constant, Λ, of the IRAsource was evaluated to be equal to 1.112 ± 0.005 cGy h U. The results of dosimetry parameters are presented in tabulated and graphical formats and compared with those reported from other commercially available HDR Ir sources, which are in good agreement. This justifies the use of specific data sets for this new source. The results obtained in this study can be used as input data in the conventional treatment planning systems. [ABSTRACT FROM AUTHOR]

The topological band structures of InAs x Sb 1 − x ( x = 0, 0.25, 0.5, 0.75, 1) alloys have been investigated using density functional theory by utilizing the Wien2k package. These alloys are in a topologically trivial phase in their unstrained states and exhibit a small band gap. Since in small band-gap cubic semiconductors the nontrivial topological phase can be achieved by lattice expansion, we investigate the effect of hydrostatic and biaxial lattice expansion on band inversion strength and band order of these alloys. It is found that under reasonable hydrostatic lattice expansion, InAs x Sb 1 − x ( x = 0, 0.25, 0.75, 1) alloys with cubic symmetry and InAs 0.5 Sb 0.5 alloy with tetragonal symmetry, are converted to nontrivial topological semiconductors with zero band gap and non-zero band gap, respectively. In order to convert InAs x Sb 1 − x ( x = 0, 0.25, 0.75, 1) alloys into topological semiconductors with non-zero band gap, we let the systems of InAs x Sb 1 − x ( x = 0, 0.25, 0.75, 1) alloys undergo a biaxial lattice expansion. Thus by breaking the cubic symmetry in these alloys, not only they are converted to topologically nontrivial phase but also a small band gap is opened at Γ point. [ABSTRACT FROM AUTHOR]