Journal of Radiation Safety and Measurement
Year:2017 | Volume:5 | Issue:3 |Papers Count:7

Radioactive 125I and 192Ir seeds are widely used as sources for interstitial implantation. 192Ir is one of the important sources frequently used in brachytherapy. Up to now, several different commercial models of this source type have been introduced to the clinical radiation oncology applications. The aim of the present study is to determine the dosimetric parameters of this new PDR Ir-192 source model. The characteristics of Ir-192 including dose rate constant, radial dose function, 2D anisotropy function was determined in PMMA phantom using TLD dosimeters. The dose rate constant was found to be 1.13±0.07cGyh-1U-1. The results of this study showed that the dosimetric characteristics of this new brachytherapy source are comparable with those of other commercially available sources.

In recent decades, radiotherapy has been had a fundamental role in the treatment of cancers. The tumor control probability (TCP) and lowest risk in normal tissue is the aim of radiotherapy techniques.The radiation sensitivity of thyroid glands increases cancer risk of scattering radiation and induces hypothyroidism. In this study, the average thyroid dose due to head and neck radiotherapy in the patients referred to Ramezanzadeh radiotherapy center of Yazd was measured. Dosimetry was achieved by TLD measurement and TPS calculations methods. The results showed that the absorbed dose of thyroid in head and neck radiotherapy and in whole-brain radiotherapy were 4.37 and 0.7 percent of the prescription dose, respectively. The mean of thyroid absorbed dose was less than the tolerance threshold dose.

In this study the attenuation ability of composites containing micro-size and nano-sized WO3 is measured and compared with the attenuation ability of composites containing micro-size and nano-sized PbO for X-rays in diagnostic energy range. For the purpose, after synthesizing nano particles and providing micro particles, different percentages of them imbedded in emulsion poly vinyl chloride (EPVC) and prepared as shields with the thickness of about 2mm and exposed in 40-100 kVp range. Transmitted dose, density and mass attenuation coefficient of prepared samples were determined and compared with previous studies. According to the results the attenuation ability of nano-particle containing shields is better than this ability for micro-particle containing ones. Also the results for WO3 containing samples differ slightly with the results of PbO containing ones. In addition all of the prepared samples have very lower density than PbO and WO3. Thus, the shields containing nano WO3 are light, flexible and could be a suitable alternative for lead aprons.

Released radioactive materials from a nuclear power plant due to an accident can be transported to far regions by wind. Some models are available to predict the dispersion. This article reports some parts of the results of a research in which using one of the models, named HYSPLIT, to predict the dispersion of some isotopes of iodine and cesium released from ten nuclear power plant to the atmosphere. These power plants are located in 20-50oN & 25-75oE. The results show that a severe accident in each of the power plants potentially are able to contaminate Iran. In nuclear emergency preparedness and response plan, source of hazards should not only be limited to Bushehr Nuclear Power Plants, but also all the nuclear power plants located in the region should be considered. The results can be used to optimize site locations for early warning monitoring stations for radioactive materials.

Microbeam radiation therapy (MRT) is an innovative experimental method used for radio resistant tumours such as glioma especially in pediatric cancer. In MRT, the patient is irradiated with arrays of parallel and high-intensity X-ray microbeams. The MRT offers dose profiles consisting of a pattern of peaks and valleys. The peak-to-valley dose ratio (PVDR) is the most important metric determining the effectiveness of MRT. Its value has to be maximized in normal tissue, and minimized in cancerous tissue in order to avoid any recovery. The main aim of this study is to investigate the possible effect of beam parameters on PVDR. To do so, the 3D dose distributions in water and head equivalent phantoms are computed with various microbeam configurations using GEANT4 simulation. The results show that the most promising PVDR are obtained at 100keV and ESRF spectrum. In addition, using a 300keV beam is not suitable for microbeams separation distance below 400mm. By increasing radiation field size, microbeam’s width and their separation, PVDR decreases for all energies. PVDRs in the bone rapidly fall because of the dominant photoelectric phenomenon for such a high-Z material.

The technology used in energy-saving compact fluorescent lamps (CFLs), provides a quarter of the energy consumption of incandescent lamps to produce equivalent light energy while CLFs shelf life is up to ten times of incandescent lamps. So the incandescent lamps in homes and workplaces are replaced with CFLs. Due to the use of ballast in the structure of CFLs, electric and magnetic fields are generated around them. Electric and magnetic fields at various frequencies can be harmful to human health.Complying with radiation exposure standards is an effective way to reduce the harmful effects of radiation. This study aimed to evaluate the electric and magnetic fields of CFLs and compare the results with standard exposure limits.Electric and magnetic fields radiated by 50 CFLs with different models, shapes and output powers at different distances from the lamps at of 50 Hz frequency and frequency range of 24 to 100 kHz were measured. Based on the measurement results, the intensities of the fields at distances greater than 50 cm is lower than the public exposure limits; however, for lamps more than 90 watts, at distances of up to 30 cm from the lamp they may be higher that exposure limits.Therefore using these lamps in small and closed places should be done with caution. Also, by increasing number of CFLs (such as for chandeliers), electric (or magnetic) vectors are added, and to meet exposure limits, more distances from the set of lamps are needed.

Treatment of radio-sensitized tumor is one of the promising modalities in radiotherapy. Since the different parameters and physical conditions vary in the treatments, the use of simulation models is easier, less costly and faster than practical methods for forecasting the solutions designed to optimize treatment. Therefore in this study, Monte Carlo simulations are applied to investigate the dose enhancement and the influential factors in photon therapy of silver nanoparticle radio-sensitized tumor. Consideration of the exact composition and sequence of the different tissues is the main task of this article. Head phantom with its actual composition was modeled by MCNPX code. Common tumor and silver nanoparticle radio-sensitized tumor are simulated. In this study, it was assumed that nanoparticles in the tumor are distributed homogeneously. Dose Calculation and its enhancement in photon therapy were calculated. The results show improved dose in the silver nanoparticles radio-sensitized tumor. This parameter is a linear function of concentration. Although silver k edge energy is 25.53 KeV, but optimized energy is between 35 to 45 KeV. Moreover, it is concluded that dose enhancement decreases by increasing the tumor depth.