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

One of the best methods for detecting breast cancer, especially in its early stages, is X-ray mammography. However, few studies have examined the risk of developing cancer in tissues other than the breast. The aim of the current study is to determine the absorbed dose in sensitive body organs during mammography. Simulation was performed using the GATE code. In the first step, an X-ray tube was created to produce suitable energy spectra for mammography. Then, a quality control phantom was designed to assess image quality, including spatial resolution and contrast-to-noise ratio (CNR). An adult ORNL phantom with different organs was designed, and the geometry of a digital mammography device was simulated in two main mammography views (CC and MLO) to calculate the dose in the organs. Finally, it was found that the radiation dose to body tissues such as the uterus, which is outside the primary X-ray field, is low (on average 0.022 μGy). However, the highest dose is received by the contralateral breast, about 2735.5 μGy, in the lungs about 48.9 μGy, in the heart about 7.6 μGy and in the stomach about 5.8 μGy after the examined breast and tumor. Based on the results, in our study, the energy of 25 keV is introduced as the optimal energy.

Proton therapy is one of the best methods of treatment for liver cancer. In this research, the main parts of proton therapy system, with passive scattering nozzle, including range-modulating wheel, energy-compensated contoured scatterer and collimators were simulated. Then the proton absorbed dose in healthy and tumoral tissues was calculated by simulating the proton therapy of liver tumors. Furthermore the secondary neutron dose, that increases the risk of secondary cancers, was calculated. For this purpose, the neutron equivalent absorbed dose in tumor and healthy tissues were calculated. Furthermore, the MIRD phantom was located in front of the output of the proton therapy system. By simulating the proton therapy for tumor in depth of 11 cm in the liver with mean source energy of 200 MeV, the absorbed dose of proton in tumor estimated as 3.32 × 10-12 Gy/particle that is 7.26 times more than proton dose in healthy parts of liver. This ratio showed that tumor absorbs the maximum dose, while the healthy tissue absorbs the minimum dose. In the next step, the same procedure was done with mean source energy of 180 MeV for tumor in depth of 6 Cm. According to the results, the proton absorbed dose in tumor was 1.94 × 10-12 Gy/particle that is 9 times more than proton absorbed dose in healthy tissue. Also the maximum neutron equivalent absorbed dose in healthy tissue is of the order of 10-14 Sv that can be ignorable in comparison with proton treatment effects of proton therapy.

The goal of this study was to investigate the dosimetric properties of magnesium oxide doped with lanthanide and indium impurities and also co-doped with lithium as a high sensitivity thermoluminescence material and its possible potential for high dose dosimetry. All the samples were synthesized by the solution combustion method and their crystalline nature was confirmed by using x-ray diffraction analysis. The morphology of the samples was characterized by scanning electron microscopy and it showed spherical particle distribution with average diameters of 158nm. Thermoluminescence response of magnesium oxide doped and co-doped with lanthanide, indium, and lithium exposed to gamma radiation within the dose range of 1 to 12kGy was measured and compared. Thermoluminescence glow curve of the samples showed a complex structure. In most cases, the thermoluminescence response of the materials to the exposed radiation was sublinear. Thermal fading of the samples was investigated and showed the remarkable result.

Radiation therapy, the most common and successful treatment used after surgery, plays an important role in the treatment of cancer. In proton therapy, the tumor is irradiated by proton beam. To increase the treatment efficacy of breast tumors, gold nanoparticles (GNP) and boron-sodium boron (BSH) solution containing boron-11 can be injected separately into the tumor and then irradiated with proton beam. In this study, using Geant4 / Gate7 simulation, confirming the increase in the dose reached the breast tumor tissue in proton therapy was performed through two separate stages, so that in the first stage, in order to maximize the received dose by protons in the tumor, injection of sodium boron captate (BSH) containing boron-11 was used in the presence of proton beam irradiation. Also, based on the injection of different concentrations of sodium boron captate solution containing boron-11 into the breast phantom, using the Monte Carlo code Geant4 / Gate7, the number of emitted alpha particles caused by the reaction  11Bp,α 8Be estimated. As a result of alpha-proton-alpha avalanche reaction, the amount of alpha particles produced by p+ 16O→α+ 13N  more than the alpha particles produced by the reaction produced due to the  11B+p→3α+8.7MeV The findings of the simulations show that the location of the Bragg peak inside the tumor changes with increasing energy to higher depths. Also, by injecting gold nanoparticles in different amounts of 25, 50 and 75 mg / ml with simultaneous irradiation of proton beam, the absorbed dose is up to 1.75% compared to the absorbed dose due to the injection of sodium boron captate solution containing boron-11 with the same values increase. In other words, the results of this study confirm the ability of gold nanoparticles to increase the effectiveness of treatment by increasing the absorption dose in breast tumors using proton therapy.

One of the most effective methods of treating thyroid cancer is iodine therapy. Patients are prescribed orally after thyroidectomy or thyroid tissue resection to control tumor growth and prevent secondary symptoms after iodine surgery. Also, due to the dose of radioactive iodine absorbed by cancer cells in the thyroid gland, it may have many side effects for those around the patient, which in this study in the radiotherapy center of Afshar Clinic in Yazd, using germanium dosimeters TLD-100 is the average absorbed dose of thyroid area on the skin surface after 24 hours to receive 100 to 150 mCi of iodine 131 and the deeply absorbed dose of thyroid at a distance of 7 cm from the skin, which includes the thyroid and surrounding soft tissue 388.933 and 379.155 cGy, respectively. After 48 hours, these values were 350.643 and 344.124 cGy, respectively. Moreover, the measured dose was around the patient. At distances of 1 to 3 m from them during 24 to 48 hours of hospitalization after radiation, iodine intake is on average 30.93 cGy, which is a high risk for those around the patient compared to the set standards. According to the results of studies published so far, age and gender are very effective in the incidence of this disease, and its prevalence is higher in women than men. Therefore, it is suggested that research be conducted on genetic factors and common underlying diseases in each region.

In this research work, hydroxyapatite was synthesized via solid-state method and effect of heat treatment on its thermoluminescence response was investigated for gamma-radiation dosimetry purposes. At the first, hydroxyapatite samples were synthesized in pure form. Then, the hydroxyapatite samples via the same synthesize method were doped with single impurities of Ce and La with concentrations of 1%, 2%, and 5% and were examined afterward.
In order to identify and evaluate the changes that occurred in the material structure and then on dosimetric response, x-ray diffraction apparatuses were used. The results were examined from different dosimetry aspects such as, glow curve change, dose response curve, reproducibility, and fading. The obtained results showed that synthesis in the higher temperature using the solid-state method, is more suitable for dosimetry purposes.

Dosimetry of a pregnant woman under diagnostic imaging with ionizing radiation is very important due to the high radiosensitivity of the fetus and the destructive effects of radiation on it. In this study, the amount of S-values induced by the positron-emitting radiopharmaceutical 18F-FDG in different fetal organs were calculated using the MCNPX2.6 Monte Carlo code. In the simulations, hybrid phantoms of 3- 6- and 9-month pregnant women were used. The results showed that with increasing the fetal age, the self S-values of fetal organs decrease. A comparison between the calculated data in this study and those reported by other studies showed similar trend, however in some cases the data difference was up to 40% on average. These differences are due to the differences between the geometry of the used phantoms. Therefore, in order to more accurately estimate the dose to pregnant patient and her fetus, we intend to introduce a method for constructing a patient-dependent phantom using a limited number of measurements in our future studies, and thus increasing the accuracy of the calculated dose.

This study aimed to produce a personal dosimeter to connect the electronic devices to transfer the dosimetry data online including dose rate data and integral dose. At first, an electronic board was designed. Afterwards, the board was simulated using Altium Designer software. Then, the microcontroller programming was performed using Code Vision software. The performance of the elements was tested using Proteus Design Suite software and the circuit diagnosis and testing were practically implemented. Afterwards, the calibration factor and the count-to-dose conversion coefficient were obtained using an ionization chamber in the Secondary Standard Dosimetry Laboratory of Iran. Furthermore, dose distribution as a function of distance to the source, was obtained using the produced dosimeter and was compared using a calibrated ionization chamber. To this purpose, an unmitigated Cs-137 source, a Cs-137 source with a 22 mm Pb shield, and a Cs-137 source with a 22 mm plus 18 mm shield were used. The results showed a calibration factor of 0.99 ± 0.02 for the designed dosimeter. Calibration results showed that the produced dosimeter passed the ISO/IEC 17025:2005 criteria. Furthermore, the dose distribution results demonstrated negligible differences of less than 0.01% between the produced dosimeter and the reference ionization chamber. It was concluded that the produced dosimeter could be used as a reference and standard dosimeter in laboratories, for monitoring and dosimetry of ionizing photon radiations.