نشریه سنجش و ایمنی پرتو
سال هفتم شماره 2 (پیاپی 27، بهار 1398)

The thymus gland is an endocrine gland that plays an important role in the body’s immunity. Thymus gland cancer happens very rarely and one treatment way is radiation therapy. Due to the location of this gland and its proximity to the sensitive organs, radiation therapy of thymus gland cancer will bring the risk of side effects. In this paper, a Mird phantom is simulated and a modulator and range compensator blades are designed to create a Spread Out Bragg Peak (SOBP) in the tumor region. The simulations are performed using the Monte Carlo GEANT4 toolkit, the FLUKA and MCNPX codes. Neutrons and photons have been considered as the most important secondary particles produced in the non-elastic nuclear interactions of protons with different elements of the body. The absorbed dose of protons and secondary particles produced during the proton therapy are calculated in the tumor, the healthy tissue of thymus gland and the 12 sensitive organs that located near this gland using these simulation tools. The results of different codes are in good agreement with each other. Results show that approximately 96 percent of the total dose is absorbed in the tumor region and the organs near the Thymus gland absorb a small amount of dose during the proton therapy.

In studying the ultraviolet (UV) radiation, one of the important factors is the possibility of generating a variety of free radicals inside the body by these radiations. In this paper, a method of estimating the amount of hydroxyl radicals produced by ultraviolet rays was investigated using nanoparticles of tin oxide doped with uropium. In this method, the change in absorption intensity of methylene blue was used as a free radical detector. SnO2:Eu nanoparticles were synthesized using co-precipitation method and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. The changes in the intensity of the methylene blue absorption curve were investigated and it was found that this intensity decreases in the presence of nanoparticles, which indicates the formation of free radicals in ultraviolet radiation. Using the results of this method, it is possible to measure the amount of received ultraviolet radiation dose.

Today, targeted radiation therapy (TRT) methods for cancer treatment, besides the goal of completely destroying the target tumor, attempts to prevent nearby healthy cells from exposure to ionizing radiation as far as possible. Hence, short-range charged particles, such as low-energy electrons that are suited to achieving these two goals together, play an important role in TRT and so, adoption of precise methods such as Monte Carlo simulations to perform cellular dosimetry of electrons and to get better knowledge of their energy deposition pattern at the cellular level is necessary. In this study, with the help of Geant4-DNA simulation code, four spherical cells (and nuclei) of liquid water in the soft tissue medium were modeled as a cell cluster. One of the cells in this model was considered as a radiation emission source of 1-10 keV monoenergetic electrons, and the energy deposition along with the S-value were calculated in this cell and its neighboring cells for different cell-to-cell distances. In addition to validating the S-values estimated by Geant4-DNA through comparing them to the values reported by Medical Internal Radiation Dose (MIRD) committee as well as the results obtained by previous version of Geant4-DNA, which shows a very good agreement, the evaluation of the results suggests that increasing the intercellular distance is significantly effective (50% or more) in reducing the energy deposition and S-value in cells adjacent to the source cell. Moreover, for electron energies of 3 keV and higher, the energy deposited in the nearby cells is such that it can cause cell destruction and death. Therefore, this is another important issue which should be considered in the selection of the suitable (electron-emitting) radiopharmaceutical as well as optimal treatment design for TRT of tumors in actual cases.

In this study, a flexible composite shield with a combination of polyethylene, tungsten and boron carbide has been designed and constructed for neutron-gamma mixed fields. For this purpose, theoretical studies were conducted using the multi-purpose MCNPX Code. According to the results of simulation studies, a multi-purpose composite was constructed using a combination of a solid phase of boron carbide particles with tungsten metal powder and a mixture of different types of soft and hard polyethylene in a laboratory at the center of polymer and petrochemical industry in Iran. The 241Am-Be neutron flux attenuation rate and the cesium gamma flux attenuation were measured for the built shield. The results show that in the polyethylene /boron carbide / tungsten (PE / B4C / w) composite with respect to the micrometric dimensions of the reinforcing particles and the high cross-section of interactions of the radioactive beams with these particles, the composite shield with a much lower thickness than the ordinary shields has higher absorption of gamma and neutron beams. This shield containing 30% of tungsten and boron with a thickness of approximately 0.5 cm, absorbs 90% of the Americium-beryllium neutrons and at the thickness of 2 cm absorbs nearly 40% of the gamma rays of the 137Cs source.

Radiotherapy includes all methods that can deliver a particular amount of ionizing radiation to malignant tissues, assuming that minimal damage hurts healthy tissues. We are looking for a valuable and reliable method to measure absorbed dose and the ability to measure the distribution of absorbed dose in three dimensions which nowadays is one of the three-dimensional dosimetry methods in using radiation-sensitive polymer gels. The purpose of the present study was to calculate the amount of increase of absorbed dose in the presence of gold nanoparticles and to investigate the type of gold nanoparticles arrangement (uniformly and shells) in the polymer gel of normoxic.
In this study from both experimental and simulation approaches, a dosimeter of a normoxic polymer type gel was used to measure the amount of absorbed dose changes of Gamma rays in the presence of gold nanoparticles irradiated with   Iridium-192 source beams. Thermolominans dosimetry reading system was used to read steps of dose value and then    MCNPX computational code was simulated by using Monte Carlo method. The results were compared and investigated by experimental experiments. In the presence of gold nanoparticles uniformly distributed in polymer gel, with 0.1mM to 1.5mM, the maximum absorbed dose was 0.24% and in shell state it was 20%. The result and investigation of both experimental and simulation studies showed that the optimum density of gold nanoparticles in the normoxic polymer gel is 1.5mM, which can be used for clinical trials.

Human tissue equivalent phantoms are widely used in medicine. They are used for dosimetry, calibration of medical devices, and quality control of radiotherapy equipment, as well as training students. Regarding to development of radiotherapy techniques for treatment of cancers and also development of educational centers in the country, the human equivalent phantoms are needed. Several phantoms have been designed and constructed over years around the world, including Rando phantom. Since Rando phantom is expensive to buy, a similar phantom has been constructed by Tabesh Pardaze Pegahs Company (TPPCO). In this study, in order to compare the constructed head phantom with the Rando head Phantom, both phantoms have been irradiated in the same gamma field. The results show that the average relative percent difference between gamma dose in constructed head phantom and Rando phantom are about 21%. More conformity with Rando phantom is achieved if some improvements are performed on the constructed phantom.

In the current research, hydroxyapatite samples, synthesized by hydrothermal methods was studied from the perspective of thermoluminescence dosimetry. The results of the study were compared and studied with different aspects of dosimetry, including dose-response variations of synthesized samples, degree of its linearity, and the percentage of response fading, as well as the position of the main peak and the degree of complexity of the glow curve. The findings show that surfactant-synthesized substances have a more optimal behavior in terms of thermoluminescence dosimetry.