جستجوی مقالات مرتبط با کلیدواژه « Dose » در نشریات گروه « فیزیک »

The most common method External radiation therapy uses beams of photons, protons, neutrons and heavy ions. The use of proton beams to treat cancer due to the Bragg peak in the target volume, causing less damage to surrounding tissue, and this is one of the benefits of this treatment.

Safe water is one of the basic needs of humans that must be free of any contamination. One of the water pollutants is radioactive nuclei, which naturally and artificially occur in the environment. Therefore, accurate measurements of water radioactivity are very important. The activity concentration of 226Ra, 232Th, 40K, and 137Cs in 26 drinking water samples from the Isfahan province was measured by gamma spectrometry using a high purity germanium detector (HPGe). Activity concentrations of 226Ra for all samples were below the detection limit. The average specific activity of radionuclides 232Th, 40K and 137Cs were measured as 1.40, 82.23 and 0.0.40 respectively in Bq/l. Annual effective doses as a result of ingestion of water containing 232Th, 40K and 137Cs radionuclides for adults ranged from 0.317 to 1.153 with an average of 0.784, from 0.059 to 0.150 with an average of 0.114 and from 0.001 to 0.016 with an average of 0.003 in μSv/y respectively. The excess lifetime cancer risk was calculated for three age groups, which was 1.59 ×10-6 for adults. The results showed that the annual effective dose as a result of drinking water consumption was lower than the WHO Individual Dose Criterion (100 μSv/y), so it does not pose a threat to the inhabitants of this area and has good quality.

Charged particles such as protons and carbon ions are an increasing tool in radiation therapy. However, unresolved physical problems prevent optimal performance, including estimating the deposited dose in non-homogeneous tissue, is an essential aspect of optimizing treatment. The Monte Carlo (MC) method can be used to estimate the amount of radiation, but, this powerful computing operation is very expensive, and has the ability to restrict it. In this work, we use basic physics in the form of the Bethe equation to provide a new analytical solution for range, energy and LET of particles. This solution is presented in terms of the functional integral by converting the relativistic harmonics, which allows it to be used at the level of radiotherapy energy (protons 50-350 MeV, carbon ions of 100-600 Mev / a.m.u). The agreement along the path of the particles, with some differences in reaching the path is high. The model presented in an optimization framework for radiation particle radiation is estimated as a rapid method for dose and LET, which is able to account for heterogeneity in electron density and ionization potential.

During radiotherapy by any radiation, it is always essential to stop absorbing the excess dose by a tissue. To better treat cancerous tissues and to make more precise irradiation for a cancerous tumor, there needs the accurate irradiation time to be estimated. First, the constituent materials of any of the existing organs in abdominal tissue are extracted and defined in the MCNPX code. Then, every organ in the abdominal tissue is voxelized by MATLAB software. Each of the voxels is defined based on Hounsfield unit of pixels in DICOM images. Then, the voxels are assigned to the related tissue which is comprised of its constituent materials, and they are filled up with them. Then, the liver tissue is segmented among the abdomen region from other tissues. Then, the geometry of the segmented liver tissue is generated as input data for MCNPX code, and the absorbed dose is computed. After obtaining the values of absorbed doses in liver tissue per each of incident fast neutron energies, the required irradiation time is obtained in second by making an appropriate proportion of absorbed dose and activity. This precise required irradiation time is obtained by an advanced software application (designed in this research using Delphi 7 programming language) through establishing a relationship between the absorbed dose and activity based upon the energy of clinical fast neutron source. The required irradiation time is calculated to reach the desired dose for each patient during fast neutron radiation therapy for similar liver tissues accordingly.

Measurement of ionizing radiation in various fields, such as environmental safety, industrial detection processes, radiation protection and medical is very important. Radiation dosimetry plays an important role in determining the amount of energy absorbed and the effects of radiation. Recent optical fiber sensors have been shown to be radiation dosimeters. Our goal here is to investigate the effect of ionizing radiation on fiber optics. Thus, in this paper, the effect of electron beam radiation on the loss of light passing through the fiber optics after the end of radiation in the wavelength range of 1300-1550 nm is investigated. Optical fibers with doses of of 22 and 47 kGy were irradiated. All measurements were carried out at a temperature of 25 ± 2 ° C. The results show that the light dissipation of the fiber optically increases with the radiation dose and decreases with the passage of time after the end of radiation.

In radiation calorimetry by using laser beams and interferometry setups, variations induced by dose absorption in phantom can be precisely measured. Dose absorption and the induced temperature change result in refractive index variation of the material. In order to be able to measure the low amount of absorbed dose in the phantom, temperature dependence of refractive index of the material must be precisely known. Water and Plexiglas phantoms can be used as tissue-equivalent materials and a multitude of reports have been published in recent years regarding their use for radiation calorimetry.  In this study, temperature dependence of refractive index of water and Plexiglas (poly- methyl methacrylate) is measured using a laser interferometry setup. The results show that the refractive index of Plexiglas has more variations with temperature compared to water. This shows that use of Plexiglas as the absorbing material for optical calorimetry, due to its nearly zero heat defect, increases the accuracy of absorbed dose measurements.

In this research, in order to improve our calculations in treatment planning for proton radiotherapy of ocular melanoma, we improved our human eye phantom planning system in GEANT4 toolkit. Different analytical models have investigated the creating of Spread Out Bragg Peak (SOBP) in the tumor area. Bortfeld’s model is one of the most important analytical methods. Using convolution method, a new analytical model for the creating of SOBP in the eye tumors was introduced. Also, the GEANT4 Monte Carlo toolkit was implemented for the Bragg peak production in the water and realistic eye phantom. Two different phantoms are proposed to study the effect of defining realistic materials on the proton dose distribution. Moreover, for the clinical investigation, the SOBP curves are figured in the water and eye phantom, using CATANA beam line. For proton pencil beams, the SOBP width for the water and eye phantoms was 0.901 and 0.877 cm, respectively. Bragg peak and SOBP calculations show a good agreement between the results of GEANT4, proposed and Bortfeld models. Using the CATANA beam line, the SOBP width difference between the two water and eye phantoms is 0.11 cm.