Introduction: Assessment of radiation dose is an important task in radiation protection dosimetry whereas absorbed and effective dose measurements directly in body organs are impossible. So Monte Carlo simulations is necessary to estimate radiation dose. The method of dose calculation, the body model and the computational code can be mentioned as three main factors that have an affect on dosimetric quantities. The aim of this study is the determination of the above factors influence on the absorbed dose and effective dose evaluation. For this purpose different comparisons between the mathematical and the voxel phantoms were done.Methods: ORNL modified adult phantom is the mathematical phantom which is described by Cristy and Eckerman in 1987. This phantom is utilized for calculation of the absorbed dose. The effective dose is calculated according to the manner which is introduced in the ICRP reported 60 and 103.Results: All of the doses Evaluation have an uncertainty less than 0.5%. MCNPX code and ORNL modified adult phantom are applied for the dose assessment in the energy range 10-9 – 20 MeV, under AP, PA, RLAT, LLAT, ROT and ISo irradiation conditions. The results are then normalized to the unit of neutron fluence. The calculated absorbed dose was compared with ICRP74 data in 9 organs and with Bozkurt et al data in 18 organs. The effective dose was calculated for whole body. Then these data were compared with results of a mathematical phantom and some voxel models in different irradiation geometries.Conclusion: Although the absorbed dose results of ORNL show fewer differences with ICRP data than Bozkurt et al data, one can deduce neither complete agreement nor disparity between the ORNL data and the other two data sets. Totally 73% of the ORNL data in comparison with MIRD data and 48% of data in comparison with VIP_MAN results have difference less than 15%. Comparison of the ORNL effective dose with some male and female voxel phantoms (TARA, HANAKO, GSF, VIP_MAN) and an analytical model (MIRD) show that the changing of body model and computational code have few influence (less than 15%) on the effective dose results. But changing of wR and wT parameters have a significant effect on the results so that the largest discrepancies are about 100% on some data.

Radiation damage depends on energy absorption, and is approximately proportional to the absorbed energy density in the tissue. In external radiation consideration with a certain energy flux, the amount of absorbed dose in each point of the tissue depends on the type of radiation, the radiation energy, the depth of the place of receipt, and the main components of the absorber environment. The absorbed energy in tissue is important in radiotherapy. This issue is well known for ionizing radiation such as X and Gamma, and is implemented in therapeutic protocols. But less attention is paid to laser therapy. Due to the actual risks of laser use, dosimeters in laser therapy are very important, in addition to observing the permissible radiation limits, in terms of radiation protection, radiation dose is required to achieve the desired effect from the requirements of this laser application in medicine.

Objective: Cosmic radiations from outer space are continuously exposing the earth. Ambient dose rate at the atmosphere, apart from unusually and transient solar activities, is mostly a function of latitude and altitude. At aircraft altitude and temperate latitudes, it increases by a factor of 20-25. Therefore, aircrew and frequent flyers are exposed to high levels of cosmic radiation. This paper considers general radiation protection aspects of cosmic radiation exposure to aircrew in domestic flights in Iran.Materials and Methods Ambient dose rate in several domestic flights was measured using survey meter model RDS-110. Based on the measured data and duration of the flight, the effective doses of the aircrew were calculated and compared with that derived from radiation transport codes of CARI-6 introduced by Civil Aerospace Medical Institute, Oklahoma City, USA. Due to good agreement between measured and calculated values, the CARI-6 program was used to determine the dose rates in different altitude throughout the country to provide a simple algorithm for calculating route dose in domestic flights.Results: Equivalent dose rate in domestic flight's altitude can be calculated from, a(h)b where h is the altitude in thousand feet; a and b are constants depending to geographic location. Based on the equivalent dose rate and the flight profile; simple algorithm provided to estimate the route dose in any domestic flights.Conclusion: The annual dose limit of general population allows the aircrew to spend 290 hour in 27-33 thousand feet altitude in domestic flights; therefore, only female aircrew should be made aware of the need to control doses during pregnancy.

Objective: Radiotherapy is one of the methods used in cancer treatment. In this method tumor cells are exposed to ionizing radiation to kill these cells. More of tumor cells are killed if exposed more radiation within the region of tumor. However, the main purpose of radiotherapy is exposing enough doses to tumor mass yet protecting the normal tissues around it. In this study, we investigate the effect of temperature on the absorbed radiation dose.Materials and Methods: In these experiments a 30 ×30 × 30 cm water phantom, Farmer ionization chamber and related electrometer were used to measure the effects of exposing g_radiation of Co-60. The field size was varied for (5×5 cm2 to 20×20 cm2) with depths (5 to 9 cm) and the range of temperatures (30 to 50oC). The curves for variation of absorbed dose at different depth at different temperatures were drawn and a temperature enhancement ratio (TER) was introduced. Results: Our results showed that TER increases for all field sizes and depths with increase in temperature. A pronounced effect was observed at temperatures higher than 42oC.Conclusion: These findings suggest that the hyperthermia (above 42oC), caused a sudden variation of the structure of water and increased the absorption of radiation dose.

The purpose of this study is to assess a rare case of fetal radiation absorbed dose here through 18 F-Fludeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) in early pregnancy (5-week-old fetus). The fetal absorbed dose due to the radiation emitted from the mother's body, the fetus self-dose, and the dose received from CT were computed. The 35-year-old patient, weighing 85 kg, was injected with 370 MBq of 18 F-FDG. Imaging started at 1 h with CT acquisition followed by PET imaging. The photon and positron self-dose was calculated by applying the Monte Carlo (MC) GATE (GEANT 4 Application for Tomographic Emission) code. The volume of absorbed dose from the mother's body organs and the absorbed dose from the CT were added to the self-dose to obtain the final dose. The volume of self-dose obtained through MC simulation for the fetus was 3. 3 × 10-2 mGy/MBq, of which 2. 97 × 10-2 mGy/MBq was associated with positrons and 0. 33 × 10-2 mGy/MBq was associated with photons. Biologically, the absorbed dose from CT, 7. 3 mGy, had to be added to the total dose. The absorbed dose by the fetus during early pregnancy was higher than the standard value of 2. 2 × 10-2 mGy/MBq (MIRD DER) because, during the examinations, the mother's bladder was full. This issue was a concern during updating standards.

Background: Nnewi town has undergone a marked increase in industrialization over the years. Considering the continuous disposal of automotive and hospital wastes in dumpsites within the town there is a need to ascertain the background radiation level of some of its dumpsites. Objective: To evaluate the level of background radiation in some selected dumpsites in Nnewi and compare the background radiation dose levels with the worldwide recommended average natural dose of 2. 4mSv/yr to humans. Methods: The levels of background radiation in these dumpsites were estimated using a well-calibrated International Medicom CRM-100 Digital Radiation Monitor (survey meter). A cross-sectional survey was adopted for this study. Following the standard procedure, the radiation monitor was held at a distance of 1. 0 meters above the ground and three readings are taken at each location and the mean recorded. The Annual Absorbed Dose Rate (ADR), Absorbed Dose Rate (AD) and the Annual Equivalent Dose Rate (AEDR) were calculated. Descriptive statistics were used to summarize the data using Statistical Package for Social Sciences SPSS version 20. Results: The mean of the calculated Annual Absorbed Dose Rates recorded at 21 and 24 meters was marginally greater than the accepted exposure rate for the public with the values of 1. 5 mSv/year respectively. At 12 and 27 meters, the values were 1. 5 mSv/year for Bank Road dumpsite respectively. Other distances were below the limit of 1mSv/year for the public and also below the dose limit of 20mSv/year for radiation workers as recommended by the ICRP. Conclusion: The radiation levels emitted from the study area were within permissible limits for the general population. Therefore there is little risk of instantaneous radiation hazard with an estimated safety zone at 6 meters from the dumpsites.

Introduction: This study aimed to investigate the absorbed dose of scatter radiation in coronary angiography. Material and Methods: The scatter radiation dose was measured for 20 patients at four different heights (50, 100, 150, and 165 cm) from the floor. The spatial dose was measured by RTI Piranha r100b solid-state dose probe at different points around the patient in an actual clinical situation and with a phantom. Also, the measurement was repeated using a designed phantom in fluoroscopy and cine mode in posterior anterior (PA), left lateral (LLAT), left posterior oblique (LPO45°, ), right posterior oblique (RPO45°, ), and right-lateral (RLAT)projections. Organ-absorbed doses were normalized to dose area product (DAP). Results: The dose rate at different heights between the projections on the patient and the phantom as well as organ dose DAP conversion coefficients were different (p˂, 0. 05). It was found that the dose rate changes in fluoroscopic mode compared to cine mode are significantly different (p = 0. 001). The dose rate in cine mode is approximately four times that in fluoroscopy mode. The dose rate around the cardiologist's waist could be reduced by 37 –,43 % with a displacement of 20cm away. In this study, the effective dose rate received by the cardiologist’, s eyes was higher than those reported by ICRP. Conclusion: Taking a suitable projection could reduce the dose rate delivered to the angiography team. Further studies should be conducted about the effect of different projections with the same clinical use on dose distribution in coronary angiography to provide the best working conditions for physicians and staff.

Background: Advances in radiation dosimetry concepts and the development of primary measurement standards based on absorbed dose to water over the last decades offer the possibility to calibrate ionisation chambers directly in terms of absorbed dose to water. The aim of this study is the investigation on utility of artificial body fluid (ABF) instead of water by comparing dosimetric measurements for radiotherapy between water and ABF which is more close to human tissue.Materials and Methods: The measurements were done using 60Co gamma source with a radiationfield sizes of 5×5, 10×10, 15×15, 20×20 and 25×25 cm2 at PTW Freiburg MP3 water phantom front surface. The comparisons of the dose measurements were obtained by using IAEA TRS-398 dosimetry protocols and Mephysto mc2 dose analyzer program. Percent depth dose (PDD), dose profiles and penumbras are compared for water and ABF.Results: When the results of the PDD for water and ABF were compared, the maximum difference was observed in big field sizes. The difference in penumbras was found 2.3 mm averagely for depth of maximum dose (dmax). In addition same differences were observed between water and ABF when the dose profiles were compared. It is found that PDD values taken for water are good agreed with PDD values published in British Journal of Radiology (BJR) Supplement 25.Conclusion: Since the ABF is more equivalent to human tissue than water, it is suggested that advanced dosimetric studies should be performed with ABF instead of water.

Panoramic radiography is one of the important diagnostic methods in dental radiology. Since this method has been used commonly in recent years, the assessment of absorbed doses received by critical organs in this radiographic technique is necessary. In this research, the absorbed doses of the eyes, parotids and thyroid glands were measured for 40 adult patients undergoing panoramic examination using Planmeca Panoramic Systems. To assess the dose, LiF thermoluminescent dosimeters were calibrated and placed on the above organs and the mean absorbed doses of the eyes, parotids and thyroid gland at two radiology centers of Isfahan (center 1 and 2). The values estimated for the eyes, parotids and thyroid at center 1 and 2 were: 91.5±10.0, 84.3±7.3, 2723±54.3 and 2657±72.4, 1514±28.4, 1461 ±40.0 micro- Gray respectively. Statistical tests revealed no significant difference (P>0.05) between the absorbed doses of the right and left eyes, the right and left sides of parotid glands and the right, middle and left parts of thyroid. These findings were expected considering the way the panoramic systems operate. On the other hand, the results acquired from the both centers were compared with each other. Analysis of the data revealed significant differences (P<0.05) between the two centers for all the organs. The reason for the differences observed may be the more workload of the center 1 and the lack of periodical calibration of the panoramic systems studied. It was also noted that the absorbed doses of the eyes estimated in this study were significantly lower than the dose limit recommended by the ICRP for the eyes. It is worth mentioning that although the estimated absorbed doses received by the organs/tissues of interest were quite low for the panoramic radiography techniques investigated in this study, according to the ALARA (As Low As Resonable Achievable) principles and because this imaging technique may be used frequently and in short intervals of time, some precautions -such as periodical calibration of equipments- must be taken into consideration.