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[en] The main task of this study is to calculate the radiological hazards due to gamma rays emitted from naturally occurring radionuclides (226Ra, 232Th, 235U and 40K) in soil samples from some areas in Egypt. The mean activity concentration of 232Th, 226Ra, 235U and 40K are 26.7, 31.1, 11 and 320.1 Bq/kg, respectively. The parameters which are used to assess the radiological hazard from exposure to these soil samples are estimated. The average absorbed dose rate of the radionuclides of interest for all measured samples is 43.5 nGy/h, while the average annual effective dose in air outdoors and indoors due to gamma radioactivity are calculated to be 53.6 and 213.9 µSv/h, respectively. The data obtained by this study will offer a base for ecologists, geophysicists and soil scientists to explain and solve easier some radio-ecological problems related to the areas under investigation. The results are intended to be further used in order to develop a data base for building a radio-ecological atlas for Egypt, in the near future. (author).
[en] Present article is devoted to equivalent dose rate values on the territory of Dzhabbor Rasul District of Tajikistan. The radiation condition on the territory of Dzhabbor Rasul District of Tajikistan has been measured by dosimeters and Pack Eye complex. Monitoring has been conducted by means of unmounted method on all territory of district. In general, the value of equivalent dose rate throughout the territory is not dangerous to population from the radiation aspect.
[en] Recently developed radiochromic films can easily be used to measure absorbed doses because they do not need development processing and indicate a density change that depends on the absorbed dose. However, in GAFCHROMIC EBT2 dosimetry (GAF-EBT2) as a radiochromic film, the precision of the measurement was compromised, because of non-uniformity problems caused by image acquisition using a flat-bed scanner with a transmission mode. The purpose of this study was to improve the precision of the measurement using a flat-bed scanner with a reflection mode at the low absorbed dose dynamic range of GAF-EBT2. The calibration curves of the absorbed dose versus the film density for GAF-EBT2 were provided. X-rays were exposed in the range between ~0 and 120 mGy in increments of about 12 mGy. The results of the method using a flat-bed scanner with the transmission mode were compared with those of the method using the same scanner with the reflection mode. The results should that the determination coefficients (r2) for the straight-line approximation of the calibration curve using the reflection mode were higher than 0.99, and the gradient using the reflection mode was about twice that of the one using the transmission mode. The non-uniformity error that is produced by a flat-bed scanner with the transmission mode setting could be almost eliminated by converting from the transmission mode to the reflection mode. In light of these findings, the method using a flat-bed scanner with the reflection mode (only using uniform white paper) improved the precision of the measurement for the low absorbed dose range.
[en] Cell experiments have shown the proton relative biological effectiveness (RBE) to vary with dose and linear energy transfer (LET), which has led to development of variable RBE models. The RBE is normally estimated from two independent functions, the RBEmax and RBEmin, describing the extreme RBE at low and high doses. While there is consensus that RBEmax increases with increasing LET, the RBEmin is not uniformly defined and its dependency on LET is deviating. In this work, we analysed this dependency and its sensitivity to variations of the experimental dose range. We performed a literature search to find data from existing monoenergetic proton cell survival experiments with (α/β)x values below 5 Gy and dose averaged LET (LETd) values below 20 keV µm−1. From the experiments the doses and their corresponding survival data were extracted. Based on these data, multiple restricted databases were generated by sequential exclusion of low dose data in the experiments followed by a linear-quadratic (LQ) fit. The quadratic component from the LQ-fit was used to estimate RBEmin. The LETd dependency of RBEmin was determined by fitting a linear function to the RBEmin values estimated from the restricted databases. Our analysis showed the LETd dependency of RBEmin to be significantly influenced by the experimental dose range. By including experiments with doses below 1 Gy in the database, we found that RBEmin increased with increasing LETd. By excluding the low dose experiments in our database, the RBEmin became constant for all LETd values. For an LETd value of 5 keV µm−1, a restricted database including the data with the lowest doses gave an RBEmin of 1.4 ± 0.1, while databases with only high dose data (>2 Gy) gave an RBEmin of 1.0 ± 0.1. None of our restricted databases gave a decreasing RBEmin with increasing LETd. Our study showed that RBEmin has a small yet significant dependency on LETd for tissues with low (α/β)x ratio. The LETd dependency of RBEmin varied substantially with the experimental dose range. Including experiments with high minimum dose in RBE models may lead to underestimation of the RBE. (paper)
[en] We developed and evaluated a novel inverse optimization (IO) model to estimate objective function weights from clinical dose-volume histograms (DVHs). These weights were used to solve a treatment planning problem to generate ‘inverse plans’ that had similar DVHs to the original clinical DVHs. Our methodology was applied to 217 clinical head and neck cancer treatment plans that were previously delivered at Princess Margaret Cancer Centre in Canada. Inverse plan DVHs were compared to the clinical DVHs using objective function values, dose-volume differences, and frequency of clinical planning criteria satisfaction. Median differences between the clinical and inverse DVHs were within 1.1 Gy. For most structures, the difference in clinical planning criteria satisfaction between the clinical and inverse plans was at most 1.4%. For structures where the two plans differed by more than 1.4% in planning criteria satisfaction, the difference in average criterion violation was less than 0.5 Gy. Overall, the inverse plans were very similar to the clinical plans. Compared with a previous inverse optimization method from the literature, our new inverse plans typically satisfied the same or more clinical criteria, and had consistently lower fluence heterogeneity. Overall, this paper demonstrates that DVHs, which are essentially summary statistics, provide sufficient information to estimate objective function weights that result in high quality treatment plans. However, as with any summary statistic that compresses three-dimensional dose information, care must be taken to avoid generating plans with undesirable features such as hotspots; our computational results suggest that such undesirable spatial features were uncommon. Our IO-based approach can be integrated into the current clinical planning paradigm to better initialize the planning process and improve planning efficiency. It could also be embedded in a knowledge-based planning or adaptive radiation therapy framework to automatically generate a new plan given a predicted or updated target DVH, respectively. (paper)
[en] This study aims to measure accumulating equivalent dose to the radiological workers (operator) under inspection cars drivers and then compare with constrains of radiation exposure used by other countries which use these systems as a first step to put the local limitations. The last published version of IAEA (G SR. Part no. 3) in 2011 mentioned that using of these systems are forbidden only after prevented the obtaining the justifications of the regulatory body for each country, knowing that it is a modern practice in the world and until now there are no such limitations in most countries. Some red eye devices have been given to the number of truck drivers of petroleum transport products and instructed them to pass through the scan system with different speeds to measure the accumulating equivalent doses in the truck drivers under inspection, radiological workers, and general people. The results accumulated equivalent doses were compared with theory results of the systems and also with documented results in the operation manual. The results showed that the doses are within the limitations only in the commitment with limitation documented in the operation manual of system.
[en] Radiochromic film dosimeters have a disadvantage in comparison with an ionization chamber in that the dosimetry process is time-consuming for creating a density-absorbed dose calibration curve. The purpose of this study was the development of a simplified method of creating a density-absorbed dose calibration curve from radiochromic film within a short time. This simplified method was performed using Gafchromic EBT3 film with a low energy dependence and step-shaped Al filter. The simplified method was compared with the standard method. The density-absorbed dose calibration curves created using the simplified and standard methods exhibited approximately similar straight lines, and the gradients of the density-absorbed dose calibration curves were -32.336 and -33.746, respectively. The simplified method can obtain calibration curves within a much shorter time compared to the standard method. It is considered that the simplified method for EBT3 film offers a more time-efficient means of determining the density-absorbed dose calibration curve within a low absorbed dose range such as the diagnostic range. (author)
[en] The test of concentric and centric rings allows to estimate the absorbed dose in people exposed to ionizing radiation from venous blood samples. In accidents with multiple victims, There are methodologies that allow increasing the response speed. The concentric count with Triage criteria (reduction in the number of cells analyzed) allows a decrease in the time of analysis, allowing the classification of the victims in dose ranges of clinical importance. The Validation of this methodology was carried out through the participation of the Biological Dosimetry Laboratory (LDB) of the Nuclear Regulatory Authority in three intercomparison exercises: 2 organized by the Canadian Ministry of Health (international) whose objective was the determination of the absorbed dose at 10 dose points in the range of 0 to 5 Gy, with an X-ray source; and 1 exercise regional organized by the LDB in which 2 dose points were evaluated in a range of 0 to 0.5 Gy with a source of Ir-192. The results showed a better fit for doses less than 2.5 Gy, with a tendency to overestimate for larger doses. However, for doses close to the limit of detection, greater uncertainty was observed in the dosimetric estimation. These exercises show that the analysis of 50 metaphases provides enough information to perform a classification of victims in dose ranges for medical decision making, allowing the use of this methodology for the purpose of mutual assistance in the region. (author)
[en] Clinical studies have demonstrated that HPV induced tumors constitute a specific subclass of cancer with a better response to radiation treatment. The purpose of this study was to investigate meaning of viral E2-gene for radiosensitivity. W12 cells contain episomal HPV 16 genomes, whereas S12 cells, which derive from the W12 line, contain HPV DNA as integrated copies. Clonogenic survival was analyzed using 96-well in vitro test. Using flow cytometry cell cycle analyses were performed. Expression of pRb and p53 were analyzed using intracellular staining. W12 cells (intact E2 gene) showed a lower survival fraction than S12 cells. W12 cells developed a G2/M block 24 h after irradiation with 2 Gy whereas S12 showed no G2/M bloc. After irradiation S12 cells developed polyploidy and pRb-positive cells decreased. W12 cells showed no change of pRb-positive cells. Depending on E2 gene status differences in cell cycle regulation might cause radioresistance. The E2/E7/pRb pathway seems to influence HPV-induced radiosensitivity. Our experiments demonstrated an effect of HPV on radiosensitivity of cervical keratinocytes via viral transcription regulator E2 pathway