Dose Rate Reduction Research Articles

Dosimetric effects of composition, location and size of tissue heterogeneities on 252Cf neutron brachytherapy

The purpose of this study is to evaluate the effect of tissue heterogeneities on dose distribution in Californium-252 (252Cf) neutron brachytherapy. The effect of location and size of heterogeneity on dose distribution was also evaluated. Neutron and photon dose rate distributions were determined in a water phantom in presence of air, lung, soft tissue and bone heterogeneities using MCNPX code. To benchmark the Monte Carlo simulation of the 252Cf source, air kerma strength (SKN), dose rate constant (ɅN) and radial dose function (gN(r)) were calculated and compared with previously reported data. Results showed a considerable reduction of neutron dose rate (up to 66%) inside heterogeneities, especially in air and bone heterogeneities, while the reduction of total photon dose rate was found less significant (up to 10%). In the presence of a heterogeneity, dose rate, fluence and energy spectrum were significantly different with respect to the homogenous phantom. The contribution of photon dose to the total dose in the presence of air and bone was dominant, compared to the neutron dose, whereas this photon contribution was reduced after passing the heterogeneity. As the bone heterogeneity size was increased from 1 × 1 × 1 cm3 to 1 × 3 × 1 cm3, the total dose and neutron energy fluence decreased of about 50% and 70%, respectively.

Use of the Intratumoural Anticancer Drug Tigilanol Tiglate in Two Horses

Tigilanol tiglate is a novel small molecule approved as a veterinary pharmaceutical in Europe for intratumoural treatment of non-metastatic, non-resectable canine mast cell tumors. The drug has a “tumor agnostic” mode of action associated with induction of an acute inflammatory response at the treatment site, immune cell recruitment, and disruption of tumor vasculature. Consequently, tigilanol tiglate has potential in treating a range of tumor types in humans and companion animals. However, it is likely that species-specific dosing and concomitant medication protocols will be required, especially to manage the drug-induced acute inflammatory response at the treatment site. As an initial step in evaluating tigilanol tiglate for treating cutaneous tumors in horses, we developed an equine-specific protocol involving (a) a 30% reduction in intratumoural tigilanol tiglate dose rate compared to that used in dogs, and (b) a regime of concomitant medications to manage the drug-induced acute inflammatory response at the treatment site. Here we report a preliminary study in two horses using the protocol to treat (i) an aggressive fibroblastic sarcoid that had recurred following surgical excision and (ii) a fast-growing peri-ocular squamous cell carcinoma. Clinical response to tigilanol tiglate treatment in these cases was similar to that observed in canine and human patients. Localized inflammation and bruising developed rapidly at the treatment site with haemorrhagic necrosis of the tumor evident within 24 h. Slough of necrotic tumor mass occurred within 6–16 days followed by infill of the tissue defect and full re-epithelialisation of the treatment site with good functional outcome. Drug-induced inflammation and oedema at the treatment site were well controlled by the concomitant medications and largely resolved within 3 days, while the wound that formed following tumor slough healed uneventfully. Both patients displayed minor lethargy during the first 36 h after treatment and localized treatment-site discomfort was apparent over the first 3–5 days. There was no evidence of recurrence of the sarcoid at 93 days, or the squamous cell carcinoma at 189 days. The results from this study support continued development and evaluation of tigilanol tiglate as a potential future treatment option for cutaneous equine tumors.

Averting cumulative lifetime attributable risk (LAR) of cancer by decontamination of residential areas affected by a large-scale nuclear power plant fallout: time aspects of radiological benefits for newborns and adults

The averted cumulative lifetime attributable risk (LAR), the residual dose and highest ground deposition of 137Cs complying with a reference dose level of 20 mSv yr−1 to an individual returning after one year to an area contaminated by unfiltered releases of fission products from a nuclear power plant (NPP) were evaluated by applying an existing exposure model designed to compute age- and gender-dependent time-integrated LAR. The model was applied to four types of nuclear fallout scenarios, partly based on data from the Chernobyl and Fukushima releases and from theoretical source terms from Swedish NPPs. For rapid decontamination measures that achieve a 50% relative reduction in external dose rate within 1 year, compliance with the reference level 20 mSv yr−1 can be attained for an initial 137Cs ground deposition of up to 2 MBq m−2 with relaxed food restrictions. This compliance can be attained at even higher ground deposition (up to 4.5 MBq m−2) if using the strict food restrictions employed in Japan after 2011. Considering longer than 1 year return times it was also found that the benefit of implementing decontamination decreases rapidly with time (2–3 years half-time), especially if the fallout has a high initial 134Cs to 137Cs activity ratio and if the ecological half-time of the external dose rate is short (<5 years). Depending on fallout scenario the averted cumulative LAR for newborn girls by decontamination that is achieved after 5 years is only between 6% and 11% of that obtained by evacuation alone during the same time, indicating a rather limited radiological benefit of decontamination if delayed more than a few years. We conclude that decision makers and emergency response planners need to consider that protracted decontamination measures may have limited radiological benefit compared with evacuation in terms of averted future cancer cases, albeit it may have other societal benefits.

Monte Carlo dosimetric characterization of a new high dose rate Yb brachytherapy source and independent verification using a multipoint plastic scintillator detector.

A prototype Yb source was developed in combination with a dynamic rotating platinum shield system (AIM-Brachy) to deliver intensity modulated brachytherapy (IMBT). The purpose of this study was to evaluate the dosimetric characteristics of the bare/shielded Yb source using Monte Carlo (MC) simulations and perform an independent dose verification using a dosimetry platform based on a multipoint plastic scintillator detector (mPSD). The TG-43U1 dosimetric parameters were calculated for the source model using RapidBrachyMCTPS. Real-time dose rate measurements were performed in a water tank for both the bare/shielded source using a custom remote afterloader. For each dwell position, the dose rate was independently measured by the three scintillators (BCF-10, BCF-12, and BCF-60). For the bare source, dose rate was measured at distances up to 3cm away from the source over a range of 7cm along the catheter. For the shielded source, measurements were performed with the mPSD placed at 1cm from the source at four different azimuthal angles ( , 9 , 18 , and 27 ). The dosimetric parameters were tabulated for the source model. For the bare source, differences between measured and calculated along-away dose rates were generally below 5-10%. Along the transverse axis, deviations were, on average (range), 3.3% (0.6-6.2%) for BCF-10, 1.7% (0.9-2.9%) for BCF-12, and 2.2% (0.3-4.4%) for BCF-60. The maximum dose rate reduction due to shielding at a radial distance of 1 cm was 88.8±1.2%, compared to 83.5±0.5% as calculated by MC. The dose distribution for the bare/shielded Yb source was independently verified using mPSD with good agreement in regions close to the source. The Yb source coupled with the partial-shielding system is an effective technique to deliver IMBT.

Temporal Change in Radiological Environments on Land after the Fukushima Daiichi Nuclear Power Plant Accident

Massive environmental monitoring has been conducted continuously since the Fukushima Daiichi Nuclear Power accident in March of 2011 by different monitoring methods that have different features together with migration studies of radiocesium in diverse environments. These results have clarified the characteristics of radiological environments and their temporal change around the Fukushima site. At three months after the accident, multiple radionuclides including radiostrontium and plutonium were detected in many locations; and it was confirmed that radiocesium was most important from the viewpoint of long-term exposure. Radiation levels around the Fukushima site have decreased greatly over time. The decreasing trend was found to change variously according to local conditions. The air dose rates in environments related to human living have decreased faster than expected from radioactive decay by a factor of 2–3 on average; those in pure forest have decreased more closely to physical decay. The main causes of air dose rate reduction were judged to be radioactive decay, movement of radiocesium in vertical and horizontal directions, and decontamination. Land-use categories and human activities have significantly affected the reduction tendency. Difference in the air dose rate reduction trends can be explained qualitatively according to the knowledge obtained in radiocesium migration studies; whereas, the quantitative explanation for individual sites is an important future challenge. The ecological half-lives of air dose rates have been evaluated by several researchers, and a short-term half-life within 1 year was commonly observed in the studies. An empirical model for predicting air dose rate distribution was developed based on statistical analysis of an extensive car-borne survey dataset, which enabled the prediction with confidence intervals. Different types of contamination maps were integrated to better quantify the spatial data. The obtained data were used for extended studies such as for identifying the main reactor that caused the contamination of arbitrary regions and developing standard procedures for environmental measurement and sampling. Annual external exposure doses for residents who intended to return to their homes were estimated as within a few millisieverts. Different forms of environmental data and knowledge have been provided for wide spectrum of people. Diverse aspects of lessons learned from the Fukushima accident, including practical ones, must be passed on to future generations.

COVERING THE PATIENT'S ARM SUPPORT IN LEAD REDUCED THE RADIATION DOSE RATE TO THE CARDIOLOGISTS DURING PERCUTANEOUS CORONARY INTERVENTIONS: A PHANTOM STUDY.

The aim of the study was to estimate organ dose rate reduction to a female anthropomorphic phantom, which simulated the cardiologist, during percutaneous coronary interventions (PCI) when the patient's arm support was covered with 0.4-mm lead foil. Organ dose rates were determined using five radiation detectors inserted into the left eye, left thyroid, left breast, left liver lobe and uterus of the phantom. A male anthropomorphic phantom was placed on the examination table of an angiography system. Heart images of the patient phantom were acquired under 10 gantry angulations typical for PCI. The lead-covered arm support did not interfere with any of the cardiac images. The median organ dose rate reductions to the left eye, left thyroid, left breast, left liver lobe and uterus were 7.8, 36.0, 28.8, 35.7 and 33.5%, respectively. The lead-covered arm support substantially reduced scattered radiation to the female cardiologist without interfering with clinical environments.

Dose Rate Analysis of Upgraded Storage Drums for Disused Sealed Radioactive Sources by a Multivariate Interpolation Program Developed Using MCNP5

The DOST-PNRI maintains a centralized radioactive waste management facility (RWMF) that performs conditioning of disused sealed radioactive sources (DSRS). These radioactive wastes are encapsulated in stainless steel and deposited into storage drums, which are in turn piled within the facility. This work describes the enhancement of the storage drum design using a dual-layer shielding of lead and concrete. This enables the drums to contain a total of three stainless steel encapsulations, therefore minimizing radioactive waste volumes within the facility. For this design, the MCNP5 code was used to verify that the surface contact dose rate limits will not be surpassed, for all drums to be fabricated. Each drum will be designed with a lead thickness that depends on the strength of radioactive waste to be contained. In order to account for different volumes, activities, and radionuclide types of the encapsulated waste as well as the required lead shielding, series of simulations were prepared to create a program in Microsoft Excel that will interpolate results based on these variable parameters. This program was subsequently applied to three existing source capsules. Results were verified with good agreement by PHITS Monte Carlo (MC) models. Using the program, design parameters were also optimized by acquiring the optimum source volume fractions per capsule, activity insertion ratios, and the maximum insertable radioactivity per drum. The degree of dose rate reduction within the old single-layer design and the enhanced dual-layer design was shown by mesh diagram. The interpolation program can be used as a tool for rapid fabrication of enhanced storage drums that can increase the capacity of the facility due to minimization of radioactive waste volumes.

Biological polymeric shielding design for an X-ray laboratory using Monte Carlo codes.

Photon irradiation facilities are often shielded using lead despite its toxicity and high cost. In this study, three Monte Carlo codes, EGS5, MCNPX, and Geant4, were utilized to investigate the efficiency of a relatively new polymeric base compound (CnH2n), as a radiation shielding material for photons with energies below 150keV. The proposed compound with the densities of 6 and 8gcm-3 were doped with the weight percentages of 8.0 and 15.0% gadolinium. The probabilities of photoelectric effect and Compton scattering were relatively equal at low photon energies, thus the shielding design was optimized using three Monte Carlo codes for the conformity of calculation results. Consequently, 8% Gd-doped polymer with thickness less than 2cm and density of 6gcm-3 was adequate for X-ray room shielding to attenuate more than 95% of the 150-keV incident photons. An average dose rate reduction of 88% can be achieved to ensure safety of the radiation area.

REDUCTION IN AMBIENT GAMMA DOSE RATE FROM RADIOCESIUM DUE TO SNOW COVER.

In the present study, variations in ambient gamma dose rate associated with snow cover were examined in a radioactive-contaminated site in Fukushima Prefecture, Japan. The ambient gamma dose rates decreased with increasing snow depth. The reduction trends were different between fresh snow (0.1-0.2 g/cm3) and granular snow (0.3-0.4 g/cm3) depending on snow density. Snow cover water content (snow water equivalent) calculated from snow depth and density was a key parameter governing the reduction in the ambient gamma dose rate. The ambient gamma dose rates reduced to 0.6 and 0.5 at 4 g/cm2 and 8 g/cm2 of snow water equivalent, respectively. Based on gamma-ray flux density distributions, the ambient gamma dose rates from the primary gamma rays decreased more compared to those from scattered gamma rays due to snow cover.

Feasibility of clay-shielding material for low-energy photons (Gamma/X)

Abstract While considering the photon attenuation coefficient (μ) and its related parameters for photons shielding, it is necessary to account for its transmitted and reflected photons energy spectra and dose contribution. Monte Carlo simulation was used to study the efficiency of clay (1.99 g cm−3) as a shielding material below 150 keV photon. Am-241 gamma source and an X-ray of 150 kVp were calculated. The calculated value of μ for Am-241 is higher within 5.61% compared to theoretical value for a single-energy photon. The calculated half-value layer (HVL) is 0.9335 cm, which is lower than that of ordinary concrete for X-ray of 150 kVp. A thickness of 2 cm clay was adequate to attenuate 90% and 85% of the incident photons from Am-241 and X-ray of 150 kVp, respectively. The same thickness of 2 cm could shield the gamma source dose rate of Am-241 (1 MBq) down to 0.0528 μSv/hr. For X-ray of 150 kVp, photons below 60 keV were significantly decreased with 2 cm clay and a dose rate reduction by ∼80%. The contribution of reflected photons and dose from the clay is negligible for both sources.

The deposition densities of radiocesium and the air dose rates in undisturbed fields around the Fukushima Dai-ichi nuclear power plant; their temporal changes for five years after the accident

The deposition densities of radiocesium and the air dose rates were repeatedly measured in a large number of undisturbed fields within the 80 km zone that surrounds the Fukushima Dai-ichi Nuclear Power Plant site between 2011 and 2016, and features of their temporal changes were clarified. The average air dose rate excluding background radiation in this zone decreased to about 20% of the initial value during the period from June 2011 to August 2016, which was essentially a result of the radioactive decay of 134Cs with a half-life of 2.06 y. The air dose rate reduction was faster than that expected from the decay of radiocesium by a factor of about two, with most of this reduction being attributed to the penetration of radiocesium into the soil. The average deposition densities of 134Cs and 137Cs in fields that were not decontaminated were found to have decreased nearly according to their expected radioactive decay, which indicated that the movement of radiocesium in the horizontal direction was relatively small. The effect of decontamination was apparently observed in the measurements of air dose rates and deposition densities. Nominally, the average air dose rates in the measurement locations were reduced by about 20% by decontamination and other human activities, of which accurate quantitative analysis is and continue to be a challenge. In this paper, new original data obtained during 2013–2016 were added to the previously reported data collected up to 2012, and it is discussed throughout.

Radiation protection value to the operator from augmented reality smart glasses in interventional fluoroscopy procedures using phantoms

IntroductionSmart glasses can be adapted to display radiographic images to allow clinician's gaze not to be directionally fixed or predetermined by computer monitor location. This study presents an analysis of eye lens dose during interventional fluoroscopy guided procedures, comparing fixed monitor positions against the use of smart glasses. MethodsUsing a head phantom (simulating the clinician), thermoluminescent dosimeters and lead shielded glasses, the dose to the eye was measured for different head ‘rotations and tilts’ for: gaze directed towards the main scattering source (patient/primary beam) to represent potential gaze direction if smart glasses are used; gaze directed to a range of potential computer monitor positions. An anthropomorphic pelvis phantom was utilised to simulate the patient. Accumulated dose rates (μGy sˉ1) from five 10-second exposures at 75 kV 25.2 mAs were recorded. ResultsAn average DAP reading of 758.84 cGy cm2 was measured during each 10 second exposure. Whilst wearing lead shielded glasses a 6.10 – fold reduction in dose rate to the lens is possible (p < 0.05). Influence of the direction of gaze by the clinician demonstrated a wide range of dose rate reduction from 3.13% (p = 0.16) to 143.69% (p < 0.05) when the clinician's gaze was towards the main scattering source. Increased dose rate to the clinician's eyes was received despite wearing lead shielded glasses, as the angle of gaze moved 45° and 90° from 0°. ConclusionIf the clinician's gaze is directed towards the main scattering source a potential exists for reducing eye lens dose compared with fixed location computer monitors. Introduction of lead lined smart glasses into interventional radiology may lead to improvements in patient care, reducing the need for the clinician to look away from the patient to observe a radiographic image.

Optimization of an Am-Be neutron source shield design by advanced materials using MCNP code

Nowadays, neutron sources are employing widely in many research as well as industrial and medical applications. A suitable neutron source with reasonable intensity, dimensions and weight is required in these applications. Am-Be is considered as an important and most famous neutron source,provides adequate neutron intensity for research and industrial applications. Typical shield materials of this source consist of some conventional and well known moderators as well as neutron and gamma absorbers. In many designs, a combined multi-layer configuration of these materials is required for better shielding efficiency which leads to a massive large shield design. Consequently, someone usually considers an Am-Be neutron source as a fixed one. However; some advantages are attributed to a portable neutron source in industriall applications. Some high-tech advanced materials have been proposed to reduce the weight and dimensions of shield design. These advance materials are much lighter and enhance shielding properties in a great extent. For example in neutron absorber advanced materials hydrogen and/or carbon content has been increased drastically leads to superior slowing down capability of these advanced materials in comparison to conventional competitors. The main objective of this work is dedicated to optimization of weight and dimensions in conventional 241Am-Be shield design using some state of the arts advanced materials. MCNP Monte Carlo code was employed for this purpose and equivalent neutron and gamma dose rates were calculated. The results showed that the use of advanced materials has a significant effect on total dose rate reduction. “Magnesium Borohydride” and “Kennertium” materials have the best performance in neutron and gamma dose reduction, respectively. The combination of these two materials can reduce the total dose rate in to one third of the reference value. Finally, two alternative shield designs were proposed. The first one is based on the combination of “Magnesium Borohydride” and “Kennertium”, for neutron and gamma absorption. The results showed that the volume and weight in the first case are reduced by 60% and 27%, respectively. In the second case the Kennertium was replaced by “Polyethylene-78.5% Bismuth” alloy to obtain much lighter shield design. The volume and weight in the second case were reduced by 49% and 67%, respectively.

Summary of temporal changes in air dose rates and radionuclide deposition densities in the 80 km zone over five years after the Fukushima Nuclear Power Plant accident

We summarized temporal changes in air dose rates and radionuclide deposition densities over five years in the 80 km zone based on large-scale environmental monitoring data obtained continuously after the Fukushima Nuclear Power Plant (NPP) accident, including those already reported in the present and previous special issues. After the accident, multiple radionuclides deposited on the ground were detected over a wide area; radiocesium was found to be predominantly important from the viewpoint of long-term exposure. The relatively short physical half-life of 134Cs (2.06 y) has led to considerable reductions in air dose rates. The reduction in air dose rates owing to the radioactive decay of radiocesium was more than 60% over five years. Furthermore, the air dose rates in environments associated with human lives decreased at a considerably faster rate than expected for radioactive decay. The average air dose rate originating from the radiocesium deposited in the 80 km zone was lower than that predicted from radioactive decay by a factor of 2–3 at five years after the accident. Vertical penetration of radiocesium into the ground contributed greatly to the reduction in air dose rate because of an increase in the shielding of gamma rays; the estimated average reduction in air dose rate was approximately 25% with penetration compared to that without penetration. The average air dose rate measured in undisturbed fields in the 80 km zone was estimated to be reduced owing to decontamination by approximately 20% compared to that without decontamination. The average deposition density of radiocesium in undisturbed fields has decreased owing to radioactive decay, indicating that the migration of radiocesium in the horizontal direction has generally been slow. Nevertheless, in human living environments, horizontal radiocesium movement is considered to contribute significantly to the reduction in air dose rate. The contribution of horizontal radiocesium movement to the decrease in air dose rate was estimated to vary by up to 30% on average. Massive amounts of environmental data were used in extended analyses, such as the development of a predictive model or integrated air dose rate maps according to different measurement results, which facilitated clearer characterization of the contamination conditions. Ecological half-lives were evaluated in several studies by using a bi-exponential model. Short-term ecological half-lives were shorter than one year in most cases, while long-term ecological half-lives were different across the studies. Even though the general tendency of decrease in air dose rates and deposition densities in the 80 km zone were elucidated as summarized above, their trend was found to vary significantly according to location. Therefore, site-specific analysis is an important task in the future.

Design of Band-Pass Filters by Experimental and Simulation Methods at the range of 100-125 keV of X-ray in Fluoroscopy

The determination of filters that remove low-energy and attenuate high-energy spectra does not essentially influence image quality, so it can reduce the absorbed patient dose. This work examines the impacts of thickness and filter material on contrast, resolution, absorbed patient dose and image quality. Based on the attenuation curves of elements and taking into account the cost-effectiveness and availability factors, four elements including tin, tungsten, lead and copper in different thicknesses was studied at the range of 100-125 keV. The simulations were executed using MCNPX code with an error less than 1% that represented the accuracy. Experimental data were obtained based on the results of calculations and simulations using fluoroscopy equipment. The results showed that applying the filters caused improving the resolution and image quality, and also remarkable reduction in output dose rate. In conclusion, the 0.1 mm thick lead element was taken as the most appropriate element in filtration.

Increased radiation dose and projected radiation-related lifetime cancer risk in patients with obesity due to projection radiography

Purpose. Primarily to evaluate the radiation dose delivered to patients with obesity in projection radiography and its relationship to the patient’s size. A secondary purpose is to estimate the subsequent projected radiation-related lifetime cancer risk to patients with obesity compared to normal-weight patients. Method and material. Data from 1964 patients from a bariatric clinic in the UK were reviewed with the relevant permission. 630 patients were identified to have a projection radiography history and were included in the study. Patients’ dose area product (DAP) data were collected for all projection radiography. Multiple exams in one day including a single DAP reading and exams with no records of DAP and exposure factors were excluded. Correlations were calculated and data analysed to yield the third quartile for each examination using STATA 14. Absorbed doses were generated from PCXMC simulation, utilising DAP data from this study and the UK national diagnostic reference level (NDRL), to calculate the effective risk for patients with obesity compared to patients with normal-weight. Results. Patients with obesity received higher DAPs for all examinations included in this study compared to NDRL. Abdominal and lumbar spine radiographs DAPs were the highest (17.6 and 30.31 Gy cm2) compared to the NDRL (2.5 and 4 Gy cm2). Only moderate to low correlations were found between patient’s size and DAPs in the abdomen and chest radiographs. The projected radiation-related lifetime cancer risk for patients with obesity is up to 153% higher than for adult patients with normal weight. Conclusion. Patients with obesity receive higher DAPs than normal-weight adults which may be in excess of that expected due to their size. Therefore, radiation-related lifetime cancer risk is increased in patients with obesity as a result of medical radiation exposures. This indicates more dose optimisation research is needed in this group of patients to reduce dose rate and variation.

Characterizing regional-scale temporal evolution of air dose rates after the Fukushima Daiichi Nuclear Power Plant accident

In this study, we quantify the temporal changes of air dose rates in the regional scale around the Fukushima Dai-ichi Nuclear Power Plant in Japan, and predict the spatial distribution of air dose rates in the future. We first apply the Bayesian geostatistical method developed by Wainwright et al. (2017) to integrate multiscale datasets including ground-based walk and car surveys, and airborne surveys, all of which have different scales, resolutions, spatial coverage, and accuracy. This method is based on geostatistics to represent spatial heterogeneous structures, and also on Bayesian hierarchical models to integrate multiscale, multi-type datasets in a consistent manner. We apply this method to the datasets from three years: 2014 to 2016. The temporal changes among the three integrated maps enables us to characterize the spatiotemporal dynamics of radiation air dose rates. The data-driven ecological decay model is then coupled with the integrated map to predict future dose rates. Results show that the air dose rates are decreasing consistently across the region. While slower in the forested region, the decrease is particularly significant in the town area. The decontamination has contributed to significant reduction of air dose rates. By 2026, the air dose rates will continue to decrease, and the area above 3.8 μSv/h will be almost fully contained within the non-residential forested zone.

PECULIARITIES OF DYNAMICS OF PERIPHERAL BLOOD CELL COMPOSITION IN CHRONICALLY-EXPOSED INDIVIDUALS IN THE PERIOD PRIOR TO LEUKEMIA DEVELOPMENT.

A retrospective analysis of the peripheral blood cell composition (PBCC) has been performed among 43 chronically-exposed Techa riverside residents later diagnosed with chronic myeloid leukemia (CML) or acute leukemias (AL). Prior to CML development, a significant increase in peripheral blood neutrophil count has been noted in exposed individuals for many years. Neutrophil count grew most significantly after reduction of exposure dose rate to red bone marrow (RBM) to ≤0.1 Gy, which was typical both for CML and AL. An increase of a relative neutrophil count remained in the CML latency period along with relative lymphocytopenia. Peculiarities of PBCC among individuals with AL at a later date were 'rejuvenation' of neutrophils in the period of maximum exposure and in leukemia latency period. During haematopoiesis restoration period, high mean values of mature neutrophils were detected in the majority of exposed individuals with AL together with decreased lymphocyte and eosinophil count. Later higher mean values of neutrophils remained in these individuals.

Issues and challenges of space radiation risk assessment in manned deep space exploration missions

The plan and implementation of manned deep space exploration missions should first ensure the health and safety of astronauts. Space radiation, mainly coming from galactic cosmic rays (GCR), solar particle events (SPE) and trapped belt radiation (TBR), has been generally considered to be one of the most important risk factors threatening the health of astronauts in deep spaceflight missions. Health risks from these exposures mainly include four aspects: carcinogenesis, acute radiation syndrome, central nervous system damage and degenerative tissue effects, and the risk of carcinogenesis remains a primary concern for manned deep space explorations. The difference in the radiation environment between the deep space and the ground leads to a high uncertainty on the estimated health risk, which is currently the main hindrance to manned interplanetary exploration. The issues and challenges related to health risk assessment of space radiation for astronauts during manned deep space exploration missions are systematically summarized and analyzed in this paper. Six main issues were raised in space radiation risk assessment, including estimation of space radiation quality, extrapolation of low-dose/dose-rate radiation risk, prediction of dose- and dose-rate reduction effectiveness factor (DDREF), screening of differences in individual radiosensitivity, effects of microgravity and other stressors on space radiation risk, and assessment of acute radiation syndromes caused by SPE. In addition, six corresponding key technologies were also discussed to address these scientific issues and challenges for future studies and practice: (1) The more dose-response data in experimental animals is needed for estimating the relative biological effectiveness (RBE) for different high-energy charged (HZE) particle types in different tissues. (2) The improved radiobiological models including targeted and non-targeted effects models, are required for accurately estimating space radiation quality factors. (3) It is necessary to accurately estimate the DDREF for low dose and dose-rate radiations, and it should be further comfirmed whether the linear-no-threshold (LNT) model is the most appropriate way to extrapolate risk estimates in low dose and dose-rate through more relevant theoretical and experimental researches. (4) The biomarker selection techniques are important to identify the potential biomarkers associated with space radiation, and the integrated risk assessment models based on the space radiation sensitive biomarkers using systems biology approaches can improve the accuracy of predicting individual radiosensitivities and disease risks induced by space radiation. (5) The influence of microgravity and other stressors on space radiation risk need to be further investigated. (6) More accurate SPE prediction models and the corresponding acute radiation risk assessment models are also necessary in further studies. The goal of reducing the uncertainties in space radiation risk assessment can be fulfilled by an international co-operative effort in these critical technologies. The arrangement and analysis of the critical issues and key technologies of space radiation risk assessment in manned deep space exploration missions can provide the strategies of reducing the health risk of astronauts induced by space radiation.

Characterizing regional-scale temporal evolution of air dose rates after the Fukushima Daiichi Nuclear Power Plant accident

In this study, we quantify the temporal changes of air dose rates in the regional scale around the Fukushima Dai-ichi Nuclear Power Plant in Japan, and predict the spatial distribution of air dose rates in the future. We first apply the Bayesian geostatistical method developed by Wainwright et al. (2017) to integrate multiscale datasets including ground-based walk and car surveys, and airborne surveys, all of which have different scales, resolutions, spatial coverage, and accuracy. This method is based on geostatistics to represent spatial heterogeneous structures, and also on Bayesian hierarchical models to integrate multiscale, multi-type datasets in a consistent manner. We apply this method to the datasets from three years: 2014 to 2016. The temporal changes among the three integrated maps enables us to characterize the spatiotemporal dynamics of radiation air dose rates. The data-driven ecological decay model is then coupled with the integrated map to predict future dose rates. Results show that the air dose rates are decreasing consistently across the region. While slower in the forested region, the decrease is particularly significant in the town area. The decontamination has contributed to significant reduction of air dose rates. By 2026, the air dose rates will continue to decrease, and the area above 3.8 μSv/h will be almost fully contained within the non-residential forested zone.