سال:1387 | دوره: | شماره: |تعداد مقالات:8

Background: A substantial part of the public’s natural radiation dose is due to the inhalation of radon gas. Most of the exposure occurs indoors where the airborne concentration of radon and its decay products is usually higher than outdoors. Materials and Methods: Radon activity concentration has been measured twice in 50 classrooms in 5 levels (10 each) during summer and winter using solid-state nuclear track detectors (CR-39). Results: The indoor radon levels in the classrooms were slightly higher than exclusion limits recommended by the ICRP in the first and second floors and fill within the safe limits in the higher floors, where the average radon concentrations were found to be 57.6 ± 3.33, 48.5±3.10, 34.5 ± 1.71, 29.7 ± 1.33 and 25.3 ± 1.88 Bq/m3 for first, second, third, fourth and fifth floors with good ventilation, respectively; and 78 ± 3.23, 66.9 ± 2.84, 40.3 ± 1.70, 34.4 ± 1.42 and 28.8 ± 1.75 Bq/m3 for classes with poor ventilation respectively. The mean annual radiation doses obtained on inhalation exposure to Rn-222 and its degradation products were 0.85 ± 0.37 and 0.67 ± 0.23 mSvy-1 for classes with closed and open windows, respectively. Conclusion: From the results obtained it can be concluded that values of radon and its daughter products and the resulting dose in the classrooms fill within the safe limit. Poor ventilation, construction materials, and radon exhalation from the ground are the main reasons for the relatively high radon concentrations in the lower levels.

Background: High and intermediate energy protons are not able to form a track in a solid state nuclear track detector (SSNTD) directly. However, such tracks can be formed through secondary particles created during primary radiation nuclear reactions in a SSNTD. Materials and Methods: The protons with primary energies of 9.6 and 30 MeV available at the cyclotron accelerator with corresponding low LETs of 5.87 and 2.40 keV/mm were taken into consideration. The nuclear tracks etch rate ratio V in CR-39 were measured and transformed into LET spectra for the absorbed and equivalent dose measurements. Results: The optimum etching condition of 6 N NaOH solutions at 65 to 70°C over a 6-hour period for the CR-39 were found initially. The corresponding bulk etching rate reached a steady rate of about 0.62 to 1.3 um/h after nine hours for an optimum etching condition. Although the LET was low, but the energy range seemed sufficient enough to create secondary particles with much higher LET through the nuclear reactions in CR-39. The relative absorbed dose contribution of the created secondary particles to the primary particles for the 9.6 and 30 MeV protons in CR-39 at 1 Gy entrance dose were 7.5 and 29.6%, respectively. Conclusion: The contribution of the secondary particle increased relatively with the proton energy decrease. This phenomenon could modify the characteristics of the energy transfer process due to secondary particles when such particles are used for radiobiological studies and/or for radiotherapy.

Background: The goals of the present research were to investigate the rectal dose during four chosen techniques of cervical cancer radiotherapy and to examine how accurately the treatment planning represents dose measurements, and it’s practicality for routine use as well as, to determine the homogeneity of dose in tumor volume. Materials and Methods: The study was carried out using a Nepton 10-PC unit and a Rando phantom. The equipments which were used for dose determination were a Radiochromic densitometer with GAFCHROMIC® film (XR type T), and a thermo-luminescent dosimeter (TLD) reader system with TLD chips for rectal and target volume dose determination. Several techniques of external beam radiation therapy such as two-field (AP-PA), three-field and four-field with equal tumor dose and with equal applied dose were planned. Results: The maximum dose received by rectum was caused by two-field technique. The results of two dosimetry types were compared with each other as well as with the treatment planning, however, no statistically significant difference was observed between them (p > 0.05). In three-field, four -field with equal tumor dose and four-field with equal applied dose, rectal dose was lower, respectively 26.17%, 33.75% and 16.47%, than tumor dose. Conclusion: This study showed that dosimetry using TLD and film during radiotherapy could have a useful role as a predictor of choosing appropriate technique for preventing future rectal complications. Dose limitation to the rectum could possibly be achieved by using three-field and four-field techniques with equal tumor dose while maintaining a high dose to the tumor.

Background: Results are presented on some dosimetric characteristics of Sife – Eldeen dosimeter based on the radiation induced conductivity (RIC) of 3.5 M aqueous urea solutions. The studied characteristics were the response (RIC) of Sife – Eldeen dosimeter in broad ranges of absorbed dose, dose rates and at different irradiation temperature. Materials and Methods: Kent EIL5007 conductivity meter (Kent industrial measurements–Brown Boveri) was used for the measurement of samples RIC. Results: RIC of 3.5M urea aqueous was studied at low (0 – 462 Gy), as well as, at high (0 - 2592 kGy) absorbed radiation dose ranges. The coefficient of variation CV%, associated with RIC measurement of 3.5 M urea solution as a function of absorbed radiation dose, was found to be not more than 3.5% for both high and low absorbed radiation dose ranges. The effect of dose rate on RIC was studied in the range 0.035 - 5.969 kGy/h. The temperature effect on this system, at different doses, was also studied. Conclusion: The obtained results show the importance of using this dosimeter for dose evaluation in industrial gamma radiation processes, as well as in medical fields.

Background: Indoor radon gas (222Rn) has been recognized as one of the health hazards for human. Air radon comes mainly from basement soil and construction materials. Saghand region with rich uranium mines lies 180 km from Yazd, so the indoor radon concentration can be high. Yazd, with population of about 457000, is the biggest city near Saghand, thus, indoor gamma background radiation of Yazd could be more than the other cities of Yazd province. Materials and Methods: In this study the air radon level of 84 dwellings basement from various regions of Yazd were measured during the year 2007. To do so, a portable radon gas surveyor was used which is an active measurement method. Using this device, α radiation of each basement was measured by a solid state detector for 24 hours. Results: Radon concentrations of the basements were between 5.55 to 747.4 Bq/m3 with mean of 137.36 Bq/m3. The mean radon concentration wasn't significantly different from the EPA guide line that is mitigation recommendations level (148 Bq/m3). However, more than 30% of the basements had radon concentration more than EPA guide line. Conclusion: Using good air conditioning system in the dwelling basements is suggested.

Background: The incorporation of thallium-201 into 8-hydroxyquinoline was targeted for cell labeling due to interesting physical properties and wide availability of this nuclide as a single photon emission computed tomography (SPECT) radionuclide. Materials and Methods: Thallium-201 (T1/2=3.04 d) in Tl+ form was converted to Tl3+ cation in presence of O3/6M HCl and di-isopropyl ether, controlled by radiothin layer chromatography (RTLC) /gel electrophoresis methods. The final evaporated activity reacted with ethanolic 8-hydroxy-quinoline (oxine) solution in normal saline to yield [201Tl](III)oxinate at room temperature after 0.5 h, followed by solid phase extraction/purification using C18 Sep-Pak column and partition coefficient determination for water/lipid solubility. In vitro red blood cell (RBC) labeling was also performed. Results: A radiochemical yield of more than 95% was obtained. Radiochemical purity of 92% was obtained using RTLC (>90% using HPLC) with specific activity of about 820 GBq/mmol. The tracer was stable in the final product and in presence of human serum at 37°C up to 6h. The partition coefficient of lopP=5.5 was obtained. The labeled compound was used in RBC labeling. The cell uptake ratio was 0.47 after 240 min. Conclusion: [201Tl](III) oxinate used in this study is a widely available agent for use in RBC labeling studies in biology, medicine and various other research areas.

Background: Sensitivity and resolution are two main parameters that have to be measured in gel dosimetry. However, the resolution in gel is strongly dependant on gel composition. Selection of optimum method in dose response readout and proper values of parameters can result in noise reduction as well as improvement of contrast, and spatial resolution considerably. Materials and Methods: MAGICA polymer gel dosimeters were manufactured and irradiated to different doses using a 60Co therapy unit. Imaging was performed in a 0.5T MRI with 8 echoes in air and water as a hydrogenous environment. Imaging condition was kept constant, as much as possible, in both imaging modalities. Results: Images obtained from these two procedures were compared quantitatively. R2- dose curves have three different sections, sensitivity obtained in these three sections were 1.039, 1.671, 1.260 Gy-1S-1 and 1.032, 1.729, 1.37 Gy-1S-1 for water and air respectively. Calibration errors were investigated and graphically were compared in two different methods. Conclusion: Imaging in water medium for doses lower than 17 Gy led to a small reduction in spatial resolution was exchanged to a considerable increase of contrast in R2 map. For doses higher than17 Gy, imaging in water or air was preferred depending on the importance of contrast or spatial resolution.

Background: Low bone mass may increase risk of fracture. Several chronic medical conditions, medications, and life style factors affect bone mineral accrual. This study aims to evaluate the bone mineral densities and hip axis lengths in the local population. Materials and Methods: 336 normal Bangladeshi women age ranges 20 to 70 years had evaluation of their bone mineral densities (BMDs) by means of dual X-ray absorptiometry (DXA). Results: The trend of BMD at the left femoral neck and the lumber spine remains fairly constant with increasing age until the 45-49 years age range, beyond which there is a consistent decline. The mean hip axis length is 10.27 cm. Conclusion: Bone mineral densities in femoral neck and lumber spine as measured by DXA and the hip axis length of the local population is lower than corresponding figures reported in the western population.