Κυριακή, 12 Μαΐου 2019

Radiation and Environmental Biophysics

Correction to: Dose–responses for mortality from cerebrovascular and heart diseases in atomic bomb survivors: 1950–2003

The article Dose–responses for mortality from cerebrovascular and heart diseases in atomic bomb survivors: 1950–2003, written by Helmut Schöllnberger.



Obituary Prof. Dr. Dietrich Harder (11 February 1930–10 February 2019)


Improved identification of DNA double strand breaks: γ-H2AX-epitope visualization by confocal microscopy and 3D reconstructed images

Abstract

Currently, in the context of radiology, irradiation-induced and other genotoxic effects are determined by visualizing DSB-induced DNA repair through γ-H2AX immunofluorescence and direct counting of the foci by epifluorescence microscopy. This procedure, however, neglects the 3D nature of the nucleus. The aim of our study was to use confocal microscopy and 3D reconstructed images to improve documentation and analysis of γ-H2AX fluorescence signals after diagnostic examinations. Confluent, non-dividing MRC-5 lung fibroblasts were irradiated in vitro with a Cs-137 source and exposed to radiation doses up to 1000 mGy before fixation and staining with an antibody recognizing the phosphorylated histone variant γ-H2AX. The 3D distribution of γ-H2AX foci was visualized using confocal laser scanning microscopy. 3D reconstruction of the optical slices and γ-H2AX foci counting were performed using Imaris Image Analysis software. In parallel, γ-H2AX foci were counted visually by epifluorescence microscopy. In addition, whole blood was exposed ex vivo to the radiation doses from 200 to 1600 mGy. White blood cells (WBCs) were isolated and stained for γ-H2AX. In fibroblasts, epifluorescence microscopy alone visualized the entirety of fluorescence signals as integral, without correct demarcation of single foci, and at 1000 mGy yielded on average 11.1 foci by manual counting of 2D images in comparison to 36.1 foci with confocal microscopy and 3D reconstruction (p < 0.001). The procedure can also be applied for studies on WBCs. In contrast to epifluorescence microscopy, confocal microscopy and 3D reconstruction enables an improved identification of DSB-induced γ-H2AX foci, allowing for an unbiased, ameliorated quantification.



Influence of the external and internal radioactive contamination of the body and the clothes on the results of the thyroidal 131 I measurements conducted in Belarus after the Chernobyl accident—Part 2: Monte Carlo simulation of response of detectors near the thyroid

Abstract

This paper describes the calculation of the response of the most common types of radiation detectors that were used within the first few weeks after the Chernobyl accident to determine the activity of 131I in the thyroids of Belarusian subjects of an epidemiologic study of thyroid cancer. The radiation detectors, which were placed against the necks of the subjects, measured the exposure rates due to the emission of gamma rays resulting from the radioactive decay of 131I in their thyroids. Because of the external and internal radioactive contamination of the monitored subjects, gamma radiation from many radionuclides in various locations contributed to the exposure rates recorded by the detectors. To estimate accurately the contribution from gamma rays emitted from various internal and external parts of the body, the calibration factors of the radiation detectors, expressed in kBq per µR h− 1, were calculated, by means of Monte Carlo simulation, for external irradiation from unit activities of 17 radionuclides located on 19 parts of the body, as well as for internal irradiation from the same 17 radionuclides in the lungs, from caesium radionuclides distributed uniformly in the whole body, and from 131I in the thyroid. The calculations were performed for six body sizes, representative of the age range of the subjects. In a companion paper, the levels of external and internal contamination of the body were estimated for a variety of exposure conditions. The results presented in the two papers were combined to calculate the 131I activities in the thyroids of all 11,732 Belarusian study subjects of an epidemiologic study of thyroid cancer and, in turn, their thyroid doses.



A study of the protective actions for a hypothetical accident of the Bushehr nuclear power plant at different meteorological conditions

Abstract

In this work, protective actions have been studied assuming a hypothetical severe accident of the Bushehr nuclear power plant at different meteorological conditions. Simulations of the atmospheric dispersion of accidental airborne releases were performed using the RASCAL code. Total effective dose equivalent (TEDE) and thyroid dose received by members of the public living within a radius of 40 km around the reactor site were calculated for various atmospheric stability classes and weather conditions. According to the results of the dose assessment and by following the protective action guide of the Environmental Protection Agency (EPA), the critical zone and appropriate protective actions were determined depending on various metrological conditions. It was found that, for atmospheric stability class F and calm weather conditions, the maximum distance from the site of release for which TEDE is greater than the corresponding dose limit and for which sheltering or evacuation response actions are required, is 11 km. For the same weather conditions, the corresponding maximum distance for which iodine prophylaxis is required is 32 km. Based on the present simulations, it can be concluded that the metrological condition has a great influence on the radionuclide atmospheric dispersion and, consequently, on the critical zone where protective actions are required after the assumed accident condition.



Efficient parameter estimation in multiresponse models measuring radioactivity retention

Abstract

After incorporation of radioactive substances, workers are routinely checked by bioassays (isotopic activity excreted via urine, measurements of radionuclides retained in the whole body or in the lungs, etc.). From the results, the isotopic activity incorporated by the worker is inferred, as well as the values of other parameters related to the metabolism of the incorporated substance, using the 'response function'. This function depends on several factors and it is usually obtained by solving a system of linear differential equations, resulting from the compartmental model which describes the human body (or a part of it). The possibility of using different types of bioassays from the same worker improves estimation of some of the parameters that characterize the solution of the system of equations, specially the unknown incorporated activity to the system. The transfer coefficients are usually considered to be known, using the values that are published in the corresponding International Commission of Radiological Protection (ICRP) publication. In the present study some practical cases will be presented, and optimal design criteria are developed that allow taking the bio-samples at the most informative times. The methodology presented here requires solving the models of element distribution in the human organism as a function of time, for which the recently updated models recommended by the ICRP have been used. Initially thought for workers in facilities dealing with radioactive substances, the study results, procedures and conclusions can be applied to other clinical or laboratory settings, and to the design of action protocols in case of environmental public exposure.



Dose optimization of lithium to increase the uptake and retention of I-131 in rat thyroid

Abstract

The present study was undertaken to optimize the dose of lithium, with an aim to increase the retention of I-131 in the thyroid follicles while maintaining the euthyroid state. 24 female Wistar rats weighing 110 ± 20 g were segregated into four groups. Animals in group I were fed standard laboratory feed and water throughout the period of experimentation. Animals in group II, III and IV were additionally fed with lithium in the form of lithium carbonate orally, at a dose of 10 mg/kg body weight, 20 mg/kg body weight, 30 mg/kg body weight respectively. The dose of lithium was started 1 week prior to radioiodine administration and continued thereafter for another 8 days. After 7 days of lithium treatment, 0.48 MBq of carrier-free I-131 was injected intraperitoneally into each rat, of the four groups. I-131 thyroidal uptake and biokinetics, as well as serum TSH, T3, T4 levels were estimated in all the treatment groups. A significant increase in the thyroid and whole body counts was observed after 4 and 24 h of I-131 aministration in lithium treated rats, compared to control animals. An increase in thyroidal effective t1/2 and serum TSH levels, along with decrease in the levels of serum T3 and T4 was observed with a dose of 20 mg/kg or higher. In Conclusion, a Lithium dose of 10 mg/kg body weight in rats could increase the uptake of I-131 in the thyroid, without disturbing the control circulating levels of thyroid hormones.



Validation of a system of models for plutonium decorporation therapy

Abstract

A recently proposed system of models for plutonium decorporation (SPD) was developed using data from an individual occupationally exposed to plutonium via a wound [from United States Transuranium and Uranium Registries (USTUR) Case 0212]. The present study evaluated the SPD using chelation treatment data, urine measurements, and post-mortem plutonium activities in the skeleton and liver from USTUR Case 0269. This individual was occupationally exposed to moderately soluble plutonium via inhalation and extensively treated with chelating agents. The SPD was linked to the International Commission on Radiological Protection (ICRP) Publication 66 Human Respiratory Tract Model (HRTM) and the ICRP Publication 30 Gastrointestinal Tract model to evaluate the goodness-of-fit to the urinary excretion data and the predictions of post-mortem plutonium retention in the skeleton and liver. The goodness-of-fit was also evaluated when the SPD was linked to the ICRP Publication 130 HRTM and the ICRP Publication 100 Human Alimentary Tract Model. The present study showed that the proposed SPD was useful for fitting the entire, chelation-affected and non-affected, urine bioassay data, and for predicting the post-mortem plutonium retention in the skeleton and liver at time of death, 38.5 years after the accident. The results of this work are consistent with the conclusion that Ca-EDTA is less effective than Ca-DTPA for enhancing urinary excretion of plutonium.



Monte Carlo-based determination of radiation leakage dose around a dedicated IOERT accelerator

Abstract

Evaluating the stray radiation around medical electron accelerators is a mandatory issue. Surveying the radiation leakage dose is important for patients, technicians, and health physicists, due to radiation protection aspects. Consequently, radiation leakage dose around the head of a mobile-dedicated intraoperative radiotherapy accelerator (LIAC), at different electron energies and field sizes have been evaluated in this study. More specifically, the MCNPX Monte Carlo code was used to model the LIAC head, connected applicator, and employed water phantom. Radiation leakage dose around the LIAC head was calculated for different energy and field sizes through tuning the Monte Carlo results to the practically measured doses. These measurements were performed using an Advance Markus ionization chamber inside an automated MP3-XS water phantom. The good agreement between the calculated dose distributions within the water tank and corresponding dose measurements show that the simulation model of the LIAC head is appropriate for radiation leakage assessment. The obtained radiation leakage dose distribution highly depends on the electron energy and applicator diameter. With increasing the electron energy, the leakage dose decreased, while increasing the field size increased the leakage dose. It is concluded that the rate of stray radiation and leakage dose around the LIAC head in both vertical and horizontal planes were acceptable according to the recommended radiation protection criteria. To meet the recommended dose limit (100 µSv/week for controlled areas), the maximum number of patients should be kept to four patients per week inside a standard and unshielded operating room.



Thyroid doses due to Iodine-131 inhalation among Chernobyl cleanup workers

Abstract

Several hundred thousand individuals, called 'cleanup workers' or 'liquidators', who took part in decontamination and recovery activities between 1986 and 1990 within the 30-km zone around the Chernobyl nuclear power plant in Ukraine, were mainly exposed to external irradiation. However, those who were involved in cleanup activities during the 10-day period of atmospheric releases also received doses to the thyroid gland due to internal irradiation resulting essentially from inhalation of 131I. The paper presents the methodology and results of the calculation of individual thyroid doses for cleanup workers. The model that was used considers several factors, including the ground-level outdoor air concentrations of 131I at the locations of residence and work of the cleanup workers, the reduction of 131I activity in inhaled air associated with indoor occupancy, the time spent indoors, the breathing rate, which depends on the type of physical activity, and the possible intake of potassium iodine (KI) for iodine prophylaxis. Thyroid doses were calculated for a group of 594 cleanup workers with individual measurements of exposure rate against the neck, called 'direct thyroid measurements', that were performed from 30 April to 5 May 1986. The measured values of exposure rate were corrected to subtract the contribution of short-lived radioiodine isotopes in the thyroid to the detector response. The average thyroid dose due to 131I inhalation by the cleanup workers was estimated to be 180 mGy, while the median was 110 mGy. Most of the cleanup workers (73%) received thyroid doses ranging from 50 to 500 mGy. The highest individual dose from 131I inhalation among the cleanup workers with direct thyroid measurements was 4.5 Gy. To validate the model, the 131I activities in the thyroids that were calculated using the model were compared with those derived from the direct thyroid measurements. The mean of the ratios of measured-to-calculated activities of 131I in the thyroid was found to be 1.6 while the median of those ratios was 0.8. For 60 cleanup workers with direct thyroid measurements, a detailed description of hour-by-hour whereabouts and work history was available. For these cleanup workers the mean of the ratios of measured-to-calculated activities was found to be 1.2 and the median of those ratios was 1.0. These encouraging results suggest that the thyroid dose due to 131I inhalation could be estimated for Chernobyl cleanup workers with a reasonable degree of reliability even in the absence of direct thyroid measurements. However, this conclusion assumes that detailed information on whereabouts and work history could be obtained for those cleanup workers who were not measured.



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