Doses Of Alpha-particle Radiation Research Articles

Radon and environmental diseases

People are generally exposed to radiation from natural sources. Radon is the most important radiation source among natural sources. Radon is a naturally occurring, radioactive noble gas that is odorless and tasteless. Radon is normally found at very low levels in outdoor air and in drinking water from rivers and lakes but higher levels in indoor air in homes, schools, and office buildings, and in well water. When radon undergoes radioactive decay, it expels high-energy alpha particles. The alpha particle radiation dose from long-term exposure increases the chance of developing lung cancer. Radon is the second most important cause of lung cancer after smoking. There is no known threshold concentration below which radon exposure presents no risk. Even low concentrations of radon can result in a small increase in the risk of lung cancer. No study of the radon exposure-lung cancer association has been performed in Korea. What is needed is a large-scale prospective study of the association between residential radon exposure and lung cancer. The cumulative indoor radon exposure is an important environmental health hazard (carcinogen).

Dose response relationships for chromosome aberrations induced by low doses of alpha-particle radiation

Using a single colour fluorescence in situ hybridisation technique, dose-responses were derived for a range of chromosomally aberrant cell types and categories of aberrations induced in peripheral blood lymphocytes by alpha-particle radiation and analysed in their first in vitro division. For a range of doses that resulted predominantly in targeted cells receiving a single hit, i.e. 0-200 mGy, linear models fitted all the different categories of aberrant cells and aberration types but the profile of chromosome damage differed for 500 mGy, reflecting the effect of different track structure.

Immunochemical analysis of protein expression in breast epithelial cells transformed by estrogens and high linear energy transfer (LET) radiation

Breast cancer is a complex disease involving numerous genetic aberrations. Immunochemical analysis of protein expression is presented in a human breast epithelial cell line neoplastically transformed by high linear energy transfer (LET) alpha particle radiation in the presence of 17beta estradiol (E) and in the parental human breast epithelial cell line (MCF-10F) which served as a non-tumorigenic control. The aim of this work was to determine the levels of mRNA and protein expression in control and transformed cells at various stages of the neoplastic process. The levels of mRNA and protein expression of PCNA, c-fos, JNK2 and Fra-1 were increased in the transformed cell line compared to the levels in non-tumorigenic control cells. The transforming factor Rho A was significantly increased only in the tumor cell line. Furthermore, the levels of mRNA and protein expression of ErbB2 were significantly increased in the transformed cell line and in tumor cells derived from the transformed cells after injecting them into nude mice. A decrease in RbA/p48 protein expression and mRNA levels was observed in cells treated with double doses of alpha particle radiation in the presence of estrogen, regardless of tumorigenicity. Such expression was lower than that in the control untreated MCF-10F cells. In summary, these studies show that estrogen and high LET-radiation induce changes in oncoprotein expression and mRNA levels of human breast cell lines. These changes are indicative of a cascade of events that characterize the process of cell transformation in breast cancer. These results provide evidence that multiple steps with consecutive changes are involved when normal cells become tumorigenic cells as a result of alpha particle irradiation and estrogen treatments.

Comparative Stochastic Effects of Inhaled Alpha- and Beta-Particle-Emitting Radionuclides in Beagle Dogs

The stochastic effects of inhaled, insoluble particles of alpha- or beta-particle-emitting radionuclides were compared in dogs. Male and female beagle dogs were exposed briefly by nasal inhalation to relatively insoluble aerosols of (239)PuO(2) or (144)Ce in fused aluminosilicate particles (FAP) and observed for cancer for their lifetimes. The initial lung burden and retention of each radionuclide was determined by whole-body counting of the emissions from (144)Ce-(144)Pr- or (169)Yb-labeled (239)PuO(2). Lung doses were calculated for each dog from these data. The lung doses ranged from 0.21 to 1200 Gy for (144)Ce FAP and 1.6 to 58 Gy for (239)PuO(2). Dogs with doses to the lung of about 60 Gy or greater from (144)Ce or about 2 Gy or greater from (239)PuO(2) had an increased incidence of lung carcinomas. In dogs exposed to (144)Ce FAP, three organs were targets for neoplasia: lung, tracheobronchial lymph nodes, and heart. The insoluble FAP carried to the lymph nodes draining the lung delivered high radiation doses to the nodes and adjacent heart, resulting in hemangiosarcomas of these organs. In the lung, high radiation doses induced hemangiosarcomas and carcinosarcomas. At lower doses, carcinomas of various histological patterns were induced in the lung. In dogs exposed to (239)PuO(2), the lung was the sole target organ for neoplasia. Nearly all of these neoplasms were carcinomas of various histological patterns. These results indicated that relatively low doses of alpha-particle radiation can induce pulmonary cancers, but relatively large doses of beta-particle radiation are required. In addition, inhaled beta-particle emitters can also induce cancers in lung-associated lymph nodes and heart at these larger absorbed radiation doses.

Unexpected Sensitivity to the Induction of Mutations by Very Low Doses of Alpha-Particle Radiation: Evidence for a Bystander Effect

We examined the induction of HPRT mutations in CHO cells exposed to low fluences of (238)Pu alpha particles from a specially constructed irradiator. The dose-response relationship was linear over the dose range of 5 cGy-1.2 Gy. However, unexpected sensitivity, leading to a significantly higher frequency of mutations than would be predicted by a back extrapolation from the data for higher doses, was observed in the dose range below 5 cGy, where the mean number of alpha-particle traversals per nucleus was significantly less than one (0.05-0.3). The frequency of mutations induced by a single alpha particle traversing the nucleus of a cell was increased nearly fivefold at the lowest fluence studied. The data are consistent with the conclusion that the enhanced efficiency of each nuclear traversal at low particle fluences is the result of mutations arising in nonirradiated, bystander cells.

Personal monitoring of 218Po and 214Po radionuclide deposition onto individuals under normal environmental exposure conditions

Personal dosemeters have been utilized to monitor the deposition of the radon decay products 218Po and 214Po onto individuals under normal environmental exposure conditions. Each detector consists of TASTRAK alpha-sensitive plastic incorporated into an ordinary working wristwatch. Subsequent analysis provides energy discrimination of the detected alpha-particle decays, and allows events from the individual radon decay products 218Po and 214Po, attached to the detector surface, to be uniquely identified. Assuming similar deposition onto skin and detector surfaces, the activity per unit area of deposited radionuclides can be determined for exposed skin. Forty-one personal dosemeters were issued to volunteers selected through the hospital medical physics departments at Reading, Northampton, Exeter and Plymouth. Each volunteer was also issued with a personal radon dosemeter to determine their individual radon exposure. The volunteers wore the two dosemeters simultaneously and continuously for a period of around one month. Correlations were observed between the radon exposure of the individual and the activity per unit area of 218Po and 214Po on the detector surface. From these correlations it can be estimated that at the UK average radon exposure of 20 Bq m-3, the number of decays/cm2/year on continuously exposed skin surface is between 3500 and 28 000 for 218Po, and between 7000 and 21 000 for 214Po. These results can be combined with theoretical modelling of the dose distribution in the skin to yield the alpha-particle radiation dose to any identified target cells.

Radon decay in bone marrow fat cells and the possible induction of leukaemia

The alpha particle radiation dose to haemopoietic stem cells and marrow was determined with Monte Carlo modeling using input data generated from autopsy specimens of normal marrow and compared with the dose estimates obtained using the Bristol image analysis and dose calculation system on those same marrow specimens. There was very good agreement between the two dose calculation methods. The project confirmed that the spatial distribution of haemopoietic stem cells in normal human marrow was random, and a trimodal distribution of haemopoietic stem cell diameters was described (possibly due to different stages of the cell cycle, as previously described in the mouse). Modeling of the dose to marrow with different fat fractions showed a positive linear relationship between the fat fraction and both the proportion of haemopoietic stem cells “hit” and the proportion of “hit” survivors. Modeling of the dose to haemopoietic stem cells in the marrow of the underground miners showed a positive linear relationship between the radon concentration in external air and both the proportion of haemopoietic stem cells “hit” and the proportion of “hit” survivors. In all the modeling the mean number of alpha particle passages per haemopoietic stem cell was approximately 1.02, with doses of 0.86, 0.20, and 0.12 Gy for haemopoietic stem cells of diameter 5.71, 11.63, and 14.79 μm, respectively.

A comparison of the risks of leukaemia and non-Hodgkin's lymphoma in the first generation offspring of the Danish Thorotrast patients with those observed in other studies of parental pre-conception irradiation

The high doses of alpha-particle radiation which Thorotrast delivers to the testes makes the study of offspring of patients, who were administered this diagnostic contrast medium, particularly relevant to the controversy regarding childhood leukaemia in the offspring of the male Sellafield workforce, as it has been suggested that the alpha-particle dose from actinides may, in part, account for the observed association between paternal pre-conception external irradiation and leukaemia. The risks of childhood leukaemia and non-Hodgkin's lymphoma found among the offspring of the male Danish cohort of neurosurgical patients injected with Thorotrast for cerebral arteriography are compared with those observed in the offspring of the Sellafield (western Cumbria), Ontario and Scottish radiation workers and in the offspring of the Japanese atomic bomb survivors. Risks are compared using linear and exponential forms of a relative risk model. The pre-conception exposure risks of leukaemia, or of leukaemia and non-Hodgkin's lymphoma, in the Danish study are statistically incompatible with the corresponding risks in the children of the Sellafield workforce ( P < 0.01), which is entirely due to incompatibility with the risks in the children of the Sellafield workforce born in Seascale ( P < 0.01). Indeed no cases arose in the Danish study. The statistical incompatibility between the offspring of the Danish patients and the Seascale-born offspring of the Sellafield workforce is independent of the models used and is insensitive to uncertainties in the gonadal dose estimates in the respective datasets or to uncertainties in the estimates of the background cancer rates in the Seascale and Danish populations. The risks of leukaemia and non-Hodgkin's lymphoma in the Danish dataset are statistically compatible with the risks observed in the offspring of the Sellafield workforce born elsewhere in western Cumbria and with those seen among the offspring of the Ontario or Scottish radiation workforces as well as with those in the offspring of the Japanese atomic bomb survivors. The statistical compatibilities of the leukaemia pre-conception exposure risks in these various groups are also independent of the models used. It is most unlikely that the Seascale childhood leukaemia cases are caused by paternal exposures to alpha-particle emitters such as plutonium. In each non-Seascale dataset the risks are consistent with there being no excess hazard of leukaemia associated with paternal pre-conception exposure to ionising radiation, and it would seem that the association seen for Seascale-born children should be attributed to chance.

Primary Liver Tumors among Danish Patients Exposed to Thorotrast

The potential carcinogenic effects of internally deposited alpha-particle-emitting nuclides, notably plutonium, in the liver in humans are unknown but are of concern in relation to exposures from the nuclear industry. However, patients injected with the radiographic contrast medium Thorotrast are chronically exposed to alpha-particle radiation from 232ThO2 in the liver. Among 1003 patients injected with Thorotrast, 584 of whom were alive 15 years after the injection and 40 at the end of follow-up, a total of 127 liver cancers were diagnosed, 45 of which were hepatocellular carcinomas, 41 cholangiocarcinomas and 33 hemangiosarcomas. The median time from injection to diagnosis was 35 years (range 18-48) and the cumulative frequency was 55.4% after 48 years. In univariate and multivariate analyses, the cumulative frequency of liver cancer was best described as a function of the estimated mean cumulative alpha-particle radiation dose to the liver 15 years ago, being independent of age, gender and volume of injected Thorotrast. This may be interpreted to mean that the liver cancer rate is not related to the dose rate and that the period from malignant transformation to diagnosis of cancer is 15 years. The risk of liver carcinogenesis induced by alpha-particle radiation, assuming 15 years from induction to diagnosis, was estimated to be 712 cases/10(4) persons per gray. This value is considerably higher than estimated earlier.

Morphological, Biochemical, and Molecular Changes in Endothelial Cells after Alpha-Particle Irradiation

The response of cultured bovine aortic endothelial (BAE) cells after exposure to alpha-particle radiation from chelated 212Bi has been evaluated. The results suggest that even relatively high doses of alpha-particle radiation from 212Bi (20-72 Gy) cause only minor acute changes in the morphology of BAE cells (light and electron microscopy) under conditions of confluent monolayer growth. Significant morphological changes can be detected in cells that detach from the monolayer, though it is unclear whether these changes represent a genuine response to irradiation or reflect the causes or effects of monolayer detachment with the consequent loss of intercellular biochemical communication. After alpha-particle irradiation (20-40 Gy) angiotensin-converting-enzyme activity was not detectable in the monolayer culture medium but was significantly decreased within the cell monolayer. Neutral-elution-assay data demonstrated that DNA double-strand-break (DSB) damage occurred in these cells and that about 35% of the DSBs were repairable.

Leukemia and Other Related Hematological Disorders among Danish Patients Exposed to Thorotrast

At least 60 case studies of leukemia among people exposed to chronic low-dose alpha-particle radiation from injections with the radiographic contrast medium Thorotrast and 115 cases from follow-up studies have been described in the literature. In the present study, malignant hematological diseases among 1003 Danish patients injected during 1935-1947 and followed to 1992 accruing 20,433 person-years were assessed and available histopathological specimens revised. The mean cumulative bone marrow alpha-particle radiation dose (1.34 Gy) was estimated from records of the amount of Thorotrast injected (mean 18.7 ml). Sixteen cases of acute myelogenous leukemia (AML) and seven cases of myelodysplastic syndrome (MDS) were diagnosed 8-40 years after injection, the cumulative frequency reaching 7.6%. No significant relationship was seen between the cumulative frequency of AML + MDS and the age at injection, gender, or amount of Thorotrast injected, but a multivariate analysis described data best by a model with the bone marrow dose and the power of the attained age. The risk estimate for AML + MDS was 173 cases/10(4) persons per Gy. If also considering cases of acute lymphocytic leukemia (1), chronic myelogenous leukemia (3), non-Hodgkins lymphoma (4), and multiple myeloma (2), the risk estimate became 248 cases/10(4) persons per Gy. It is suggested that RBE of alpha particles from thorium may be lower than 20.

Response of X-Ray-Sensitive CHO Mutant Cells (xrs-6c) to Radiation: II. Relationship between Cell Survival and the Induction of Chromosomal Damage with Low Doses of α Particles

The induction of cytotoxicity, chromosomal aberrations, and sister chromatid exchanges (SCEs) was measured in CHO K-1c cells and in isogenic X-ray-sensitive mutant xrs-6c cells that had been irradiated with X rays and alpha particles in isoleucine-deficient alpha-minimal essential medium in G1 phase of the cell cycle. There was a noticeable shoulder region on the survival curve for CHO K-1c cells irradiated with very low doses of alpha particles, whereas this feature was absent for xrs-6c cells with alpha-particle doses as low as 0.5 cGy. Higher frequencies of chromatid-type aberrations were induced in G1-phase xrs-6c cells than in G1-phase CHO K-1c cells by both gamma- and alpha-particle irradiation. Induction of nonlethal chromosomal aberrations was observed following exposure to 2-6 cGy of alpha particles, doses yielding 97-100% cell survival. Irradiation with 0.5 cGy of alpha particles induced SCE; nearly 60% of irradiated cells contained significantly increased levels of SCE. However, only 3% of the nuclei of cells exposed to 0.5 cGy of alpha-particle radiation were actually traversed by an alpha particle. The observation that a large fraction of cells apparently survive exposure to very low doses of alpha-particle radiation with persistent genetic damage manifested by both chromosomal aberrations and SCEs may have important implications for the carcinogenic hazards of high-LET radiation.

The biodistribution and toxicity of plutonium, americium and neptunium

In the nuclear fuel cycle the trunsuranic radionuclides plutonium-239, americium-241 and neptunium-237 would probably present the most serious hazard to human health if released into the environment. Despite differences in their solution chemistry the three elements exhibit remarkable similarity in their biochemical behaviour, apparently sharing similar transport pathways in blood and cells. After entering the blood the elements deposit predominantly in liver and skeleton, where retention appears to be prolonged, with half-times of the order of years. The principal late effects of all three radionuclides are the induction of cancers of bone, lung or liver. For the latter tumours the induction risk per unit radiation dose appears similar for the three radionuclides. But in bone there are indications that, due to microscopic differences in the distribution of the alpha-particle radiation dose, the efficiency of bone cancer induction may increase in the order americium-241 < plutonium-239 < neptunium-237. No case of human cancer induced by these radionuclides is known.