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A A Edwards

Publications and source records attributed to A A Edwards.

At least 19 recordsLinked to original sources
PubMed2003

The present ICRP protection quantitites are seriously flawed. Opposing the proposition.

Our debaters have agreed to defend positions that appear to be diametrically opposed; nevertheless, they have acknowledged some common ground. Although it was not explicitly stated, they would no doubt agree that workers and the public are adequately protected by our present system of radiation regulations. Our debaters have overtly agreed that it would be desirable to have measurable radiation protection quantities. Whether or not this is advantageous, or even possible, will depend upon which argument swayed your opinion. The ICRP is presently examining its recommendations and will, over the next few years, update those recommendations. Therefore, the contributions of our debaters will surely be relevant to this process.

Humans↗
PubMed2002

Modelling radiation-induced chromosome aberrations.

PURPOSE: To review the data and models on the induction of chromosomal aberrations by a single acute dose of radiation, then critically to assess progress that has been made so far to make a judgement about prospects for increased understanding. MATERIALS AND METHODS: Drawing upon many years of personal experience, a consistent set of data on the radiation-induced dicentric yield in human lymphocytes was produced. Other data concerning the production of complex rearrangements and the time-course of the appearance of dicentrics has also been reviewed. Three basic models have been reviewed and compared with respect to their ability to predict the judged dose-effect relationships as well as the time-course and complexity of the aberration production. CONCLUSIONS: None of the three basic models alone can explain adequately all of the available data. A combination of the models has succeeded to a greater extent, but there is still no complete agreement. The major reason for the discrepancy between the measured yield curves and their predictions lies in the variation of the quadratic term in the dose-response relationship with increasing linear energy transfer. Further experimental work is required to resolve this.

Animals↗
PubMed2002

Cytogenic investigations of serious overexposures to an industrial gamma radiography source.

This paper describes the sequence of events, medical aspects and dose estimations for two radiographers and their driver who were seriously exposed to an iridium-192 industrial radiography source that became detached from its wind-out cable. The men came to medical attention about 1 month later by which time all three were severely leucopenic and one had skin burns on both hands. Doses were estimated by (i) physics calculations combined with their accounts of the event. (ii) the levels of depression of their blood neutrophils, (iii) electron spin resonance on tooth enamel and (iv) blood lymphocyte chromosomal analyses by the conventional dicentric and the fluorescence in situ hybridisation methods. Intercomparison of these methods for estimating doses showed a good level of agreement. In brief, the averaged whole body dose for the most seriously exposed man was about 2.5-3.0 Gy and for the others it was 1.0-2.0 Gy.

Acute Disease↗
PubMed2001

In vitro transmission of chromosomal aberrations through mitosis in human lymphocytes.

Stable and unstable chromosome aberrations in human lymphocytes exposed to 2 and 4Gy of X-rays in G(0) were analyzed in M1 and M2 cells harvested at 72h to investigate how the scoring protocol influences the yields of aberrations transmitted through one mitosis. Metaphase chromosomes 2, 3, and 5 were painted using fluorescence in situ hybridization (FISH) whole chromosome probes, together with a pan-centromeric probe and stained by the harlequin-FISH method, to allow the cell cycle status of each cell to be determined as it was scored. A strict scoring criterion was adopted so that each metaphase had to contain 46 centromeres and each dicentric/centric ring had to have an acentric present. In addition to scoring the painted material, unstable aberrations in the whole genome were also recorded. The yield of complete dicentrics decreased by more than a factor of 2 in going from M1 to M2. The decrease was greater at the lower dose. Two-way translocations appeared stable, but one-way translocations decreased. This suggests that if translocation yields are to be used for biological dosimetry purposes, then the two-way type should be used.

Adult↗
PubMed2001

Lack of detectable transmissible chromosomal instability after in vivo or in vitro exposure of mouse bone marrow cells to 224Ra alpha particles.

Several studies over recent years have highlighted the possibility that radiation can induce transmissible genomic instability. Most of these involve in vitro irradiation and usually in vitro culture. Here it is reported that the short-half-life bone-seeking alpha-particle emitter (224)Ra did not induce excess transmissible chromosomal instability in CBA/H mouse bone marrow cells in a 100-day period after in vivo or in vitro exposure. Similarly, no excess transmissible chromosomal instability could be detected after in vivo whole-body X irradiation. It was noted, however, that short-term culture of murine bone marrow cells elevated yields of aberrations, as did transplantation of untreated marrow into radiation-ablated hosts. These findings emphasize the sensitivity of murine hemopoietic tissue to experimental manipulation and reinforce the importance of appropriate concurrent control experiments in any investigation of transmissible genomic instability.

Alpha Particles↗
PubMed2001

A study to verify a reported excess of chromosomal aberrations in blood lymphocytes of Namibian uranium miners.

This report describes a study to verify an earlier report of excess chromosomal damage in the blood lymphocytes of uranium miners. Coded blood samples from 10 miners and 10 controls were analyzed conventionally for unstable aberrations and by FISH for translocations. Conventional analysis, scoring 1000 metaphases per subject, showed no significant difference between miners and controls in the frequencies of chromosome- and chromatid-type aberrations. Investigators at two laboratories undertook FISH analyses, each scoring 4000 metaphases per subject. When the data from each laboratory were examined separately, one found slightly more translocations in the miners while the other found fewer. In neither case was the difference significant at the 95% level of confidence. Combining the data likewise showed no significant excess of damage in the miners. This applied to simple one- and two-way translocations and to cells with complex exchanges. There was no correlation between levels of translocations and total lifetime doses from occupational and/or background irradiation. A borderline significant excess of rogue cells was found in the miners. This may be a chance observation, as these rare, highly abnormal cells are considered to be unrelated to radiation exposure and are probably due to a virus. The overall conclusion is that the frequency of chromosomal damage in the miners did not exceed that in the controls. Therefore, the result of the earlier study was not confirmed.

Chromosome Aberrations↗
PubMed2001

Lymphocyte chromosomal aberrations and their complexity induced in vitro by plutonium-239 alpha-particles and detected by FISH.

G0 human lymphocytes were exposed in vitro to plutonium-239 alpha-particles, with doses ranging from 0 to 1.62 Gy, to provide a dose response curve and to compare complex rearrangements produced by high LET radiation with low LET data from previous work. Metaphase chromosomes 1 and 2 were painted using fluorescence in situ hybridization (FISH) whole chromosome probes. All unstable and stable aberrations involving the painted chromosomes were scored. The whole genome corrected alpha-coefficient for dicentrics was 0.244 +/- 0.023 and for total translocations 0.346 +/- 0.032, when considering simple and complex exchanges. The ratio of bicoloured total translocations to bicoloured dicentrics was 1.21 +/- 0.15 and the ratio of 2-way to 1-way translocations was 1.73 +/- 0.27 for apparently simple exchanges only. A correlation was noted between the distributions of dicentrics and translocations and this applied even when the complex rearrangements were removed. 20% of the observed rearrangements were complex and this observation was independent of dose. Qualitatively, following irradiation with alpha-particles the complex rearrangements observed were of a greater complexity than seen after X- or gamma-rays. Using the Savage and Simpson system to classify the complex rearrangements, the higher order complexes were found to be the most common type observed. However the insertion type increased while the 2F + 2G types decreased when complex rearrangements induced by alpha-particles were compared to those formed after X- or gamma-irradiation.

Alpha Particles↗
PubMed2001

RBE of radiations in space and the implications for space travel.

Space travellers are irradiated with cosmic rays to a dose rate considerably higher than that received on earth. In order to make sensible judgements about space exploration, the risks to health of such radiation need to be assessed. Part of the assessment of risk is to allow for the enhanced biological effectiveness of high LET radiations with respect to others. In space the high LET radiations of concern are high energy neutrons and charged particles. At the doses and dose rates encountered in space, the important risk is the induction of cancer in the astronauts. For this biological end-point there is no direct human evidence for the relative effectiveness of these radiations. There are some data for neutrons for cancer and life-shortening in laboratory animals but these are for fission spectra neutrons, which are of lower energy than those encountered in space. There is a small amount of data for protons and high energy heavier charged particles. The remaining evidence comes from cellular experiments observing chromosome aberrations and gene mutations. From this sparse information, pragmatic choices need to be made for application to protection in space. The data are reviewed and the bases for the pragmatic choices discussed.

Animals↗
PubMed2000

The role of cytogenetics in early triage of radiation casualties.

Preliminary dose estimates by chromosomal analysis can be made rapidly in order to supplement early triage of radiation casualties based on clinical signs. An in vitro simulation of an accident with many casualties receiving whole or partial body exposure in the range 0-8 Gy is described. Faced with an urgent need for rapid results, confirmation of clinical triage can generally be obtained from scoring 20 metaphases per subject. Scoring should be increased to 50 cells where there is disagreement with the initial assessments or evidence of significantly inhomogeneous exposure.

Chromosome Aberrations↗
PubMed2000

Comparison of cytogenetic damage in cultured cells from cobalt-60 gamma-radiation and the Auger emitter zinc-65.

PURPOSE: To assess the ability of the Auger-emitting nuclide, zinc-65 (65Zn), relative to gamma-irradiation, to cause chromosomal aberrations in cultured rat prostate cells. MATERIALS AND METHODS: Rat prostate adenocarcinoma cells in culture were exposed to doses of 1, 2, 3 or 5 Gy of external gamma-irradiation for 24h or incubated with 0.7, 1.5, 1.8 or 2.8 MBq of 65Zn for 24 h. The uptake by and clearance from cells of 65Zn was measured. Metaphase spreads prepared from washed cells were scored for chromatid- and chromosome-type aberrations. RESULTS: Following exposure to 65Zn or gamma-irradiation, chromatid-type damage was more commonly observed than chromosome-type aberrations. The relationship between induced chromatid damage and gamma dose (to 3 Gy) was best fitted by a second-order polynomial function, while the activity response relationship for chromatid damage caused by 65Zn appeared to be best fitted by a straight line. Measurements of the uptake of 65Zn by cells showed that average concentrations within cells were about 100 times the concentration in the culture medium. Assuming uniform distribution of 65Zn within cells, with 36% in the nucleus, the dose was estimated as 0.70 Gy per MBq added 65Zn, with Auger electrons contributing most (93%) of the dose. Assuming that 20% of cellular zinc was localized in the nucleus, based on previous measurements, the dose to the nucleus was calculated as 0.44 Gy per MBq added 65Zn. RBE values for chromatid damage induced by 65Zn compared to gamma-radiation range from about 1 to 3 based on a uniform dose throughout the cell and from about 2 to 5 based on 20% of 65Zn in the cell nucleus. CONCLUSION: The observed radiotoxicity of 65Zn is consistent with its behaviour as an Auger-emitting radionuclide that is localized to some extent in the nucleus.

Adenocarcinoma↗
PubMed1999

The 60Co gamma ray dose-response for chromosomal aberrations in human lymphocytes analysed by FISH; applicability to biological dosimetry.

PURPOSE: To investigate the in vitro dose-response for 60Co irradiated human lymphocytes assayed by FISH, and to consider how this may be applied to retrospective dosimetry. METHOD: Blood was irradiated with doses in the range 0.25-4.0 Gy. Cultured lymphocytes were scored for all stable and unstable aberrations involving painted chromosomes 2, 3 and 5 and, in addition, all unstable aberrations in the counterstained chromosomes. A pancentromeric probe was included. RESULTS: The relative numbers of painted and full genome dicentrics agreed well with the Lucas hypothesis for calculating genome equivalence. The involvement of each painted chromosome in exchanges agreed with their relative arm lengths. The dose-response relationship fitted well to the linear quadratic model; Y=(0.9 x 10(-2))D+(6.5 x 10(-2))D2 where D is the dose in Gy for the incidence Y, of all one plus two-way translocations in all cells corrected for genome equivalence. Complex rearrangements also became more frequent with increasing dose. A correlation was noted between the distributions of dicentrics and translocations among the cells and this was entirely due to complexes. CONCLUSIONS: For retrospective dosimetry it is recommended to use an in vitro dose-response for apparently simple translocations in stable (Cs) cells. To date, acute linear yield coefficients from FISH data carry statistical uncertainties too large for useful application to retrospective dosimetry of persons exposed to chronic or low doses. As an interim measure it is suggested that one may derive a linear term from full genome dicentrics corrected by a factor representing the translocation to dicentric ratio.

Cells, Cultured↗
PubMed1999

Simple chromosome exchanges are not linear with dose.

PURPOSE: To check whether simple chromosome exchanges are linearly related to radiation dose. MATERIALS AND METHODS: Go-irradiated lymphocytes were cultured to produce metaphase preparations. Chromosomes 1 and 2 were painted different colours and the remaining chromosomes counterstained. Cells containing a colour junction involving both chromosomes 1 and 2 were scored fully, so that simple and complex rearrangements were distinguished. RESULTS: At doses of 2 Gy and below very few complex rearrangements were seen. About 90% of exchanges were simple. At these doses the linear component of the dose-effect curve accounts on average for only approximately 30% of the observed yield. CONCLUSIONS: There is a square-law dose component to the yield of simple exchanges in addition to the linear term.

Cells, Cultured↗