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D C Lloyd

Publications and source records attributed to D C Lloyd.

104 records · Page 6Linked to original sources
PubMed1976

Chromosome aberrations induced in human lymphocytes by neutron irradiation.

In vitro dose--response curves of unstable chromosome aberrations in human lymphocytes have been obtained for neutron spectra of mean energies 0-7, 0-9, 7-6 and 14-7 MeV. The aberration yields have been fitted to the quadratic function Y = alphaD + betaD2, which is consistent with the single-track and two-track model of aberration formation. However with high-LET radiation, the linear component of yield, corresponding to damage caused by single tracks, predominants, and this term becomes more dominant with increasing LET, so that for fission spectrum neutrons the relationship is linear, Y = alphaD. At low doses, such as those recieved by radiation workers, limiting r.b.e. values between 13 and 47 are obtained relative to 60Co gamma-radiation. At higher doses, as used in radiotherapy, the values are much lower; ranging from 2-7 to 8 at 200 rad of equivalent gamma-radiation. Both sets of r.b.e. values correlate well with track-averaged LET but not with dose-averaged LET. When the numbers of cells without aberrations are plotted against radiation dose, curves are obtained which are similar in shape to those for conventional cell-survival experiments with comparable neutron spectra. The Do values obtained in the present study are close to those from other cell system.

Chromosome Aberrations↗
PubMed1975

The relationship between chromosome aberrations and low LET radiation dose to human lymphocytes.

In vitro dose-response curves of unstable chromosome aberrations in human lymphocytes have been obtained for 250 kV X-rays and cobalt-60gamma-radiation. The aberration yields have been fitted to the quadratic function Y = alphaD +betaD2, which is consistent with the single-track and two-track model for aberration formation. The values of the coefficients alpha and beta support the hypothesis that the dose-rate effect is limited to the D2 term. The main difference between the coefficients for X- and gamma-radiation is in the alpha values, indicating that X-rays are slightly more efficient, at lower doses, in producing two lesions with a single ionizing track. The lower limits of dose estimate, with 500 cells analysed, are 4 rad for X-rays and 10 rad gamma-radiation. Further evidence is presented confirming that, for cytogenetic dosimetry, in vitro dose-response curves should be prepared by irradiating whole blood maintained at 37 degrees C and prior to PHA stimulation. Curves were plotted showing the variation of the number of cells without aberrations with radiation dose and the shape of these curves were compared with those from human cell survival experiments.

Adult↗
PubMed1975

An investigation of the characteristics of a negative pion beam by means of induced chromosome aberration in human peripheral blood lymphocytes.

The depth dose profiles of unstable chromosome aberrations were determined by irradiating blood samples at various depths in a plastic phantom exposed to a beam of negative pi mesons (pions). The pions were derived from an experimental beam line from the Nimrod 7 GeV proton synchrotron. With a momentum of 160 MeV/c and a spread of 15 per cent a Bragg profile was produced peaking at 13-9 cm. An ionization peak to plateau ratio of 1-6 was obtained and for cytogenetic damage this was increased to 2-9. Dicentric and acentric dose-response data from peak and plateau positions were fitted to Y=alphaD+betaD-2 models for comparison with data obtained from 60-Co gamma-rays and fission neutrons. With respect to 150 rads gamma-radiation, the r.b.e. values for the pion peak were 2-1 for dicentrics and 2-3 for acentrics. In the plateau the value for both aberrations was 1-5. At pion doses likely to be used as daily radiotherapy fractions, the aberrations predominantly resulted from single-track events, indicating little likelihood of interfraction recovery, particularly in the peak position. It is concluded that the biological damage characteristics of pion beams, as determined from a cytogenetic end-point, offer several features attractive to the radiotherapist.

Chromosome Aberrations↗
PubMedDate not supplied

ESR dosimetry of a deceased radiation worker.

A case of overexposure of an industrial radiographer using 192Ir sources and having a filmbadge dosimeter record of 104 mSv has been examined with ESR dosimetry of postmortem tooth and bone specimens. ESR measurements of the tooth enamel showed an intense signal of CO2- and gave the equivalent dose (ED) of 14 Gy by the additive dose method using gamma-rays from a source of 60Co. The doses for a finger bone and humerus were 14.7 and 7.0 Gy, respectively. It was concluded that he had been exposed to radiation repeatedly over 10 yr and that ESR dosimetry can give a life-long cumulative dose for personnel using radiation.

Bone and Bones↗
PubMedDate not supplied

Back pain in industry. A prospective survey.

Eight hundred and two subjects employed in N.W. England have been interviewed and examined after episodes of back or sciatic pain, using a standardized procedure. Data on recurrence of symptoms leading to further treatment or absence from work in the following two 12-month periods were obtained by postal questionary. Residual pain in the leg and a number of positive clinical signs of return to work, longer sickness--absence for the current attack, and two or more previous attacks were all associated with recurrence or persistence of symptoms. The prognosis also varied according to the cause of back pain, falls being associated not only with longer periods of absence in the current attack but with a higher rate of recurrence. The results have underlined the significance of a thorough examination on return to work after back pain for the industrial medical officer, as well as the epidemiological importance of this phase in the natural history of back and sciatic pain.

Absenteeism↗
PubMedDate not supplied

[The comparison of molecular-biochemical and cytogenetic analyses of blood cells of patients long after the acute radiation sickness].

Molecular-biochemical and cytogenetic analyses were made on blood cells of 17 radiation accident victims who, from 1.7 to 43.8 years previously, had suffered acute radiation sickness (ARS) ranging from severity grades I to IV. Molecular-biochemical data were obtained with patients' leukocytes and with mononuclear cells on their oxidative status by a) the level of an anion-radical O2*- in the 3-(4,5-dimethyl-2-thiazol-2-yl)-2,5-diphenyl-2-tetrazolium bromide (MTT) test and b) the sum of reactive oxygen species in the 2,7-dichlorodihydrofluorescein diacetate (DCFDA) test together with a test for DNA strand unwinding in alkaline conditions by measurements of fluorescence intensity of ethidium bromide. Each parameter was measured in freshly sampled cells and during a 5-hour incubation as absolute means on 5 measurements and in % change from the initial values. Cytogenetic data were obtained from the standard metaphase preparations scored for routine unstable chromosomal aberrations (us-CA)--dicentrics; and stable aberrations (sCA)--translocations. The latter ones were assayed by the FISH method using whole chromosome 2, 4 and 12 fluorescent probes and scaled up to genome equivalence. For all patients reduced oxidative status of about 25-30% was obtained by the MTT-test (p < 0.005), and the DCFDA-test (p < 0.027). The yield of usCA depended on the time after irradiation with higher yields associated with the shorter postirradiation times and reducing almost to expected background frequencies. The yield of sCA was high for all patients, correlating with the severity of ARS whilst the molecular-biochemical parameters showed no relationship with ARS. A correlation was observed between parameters of oxidative status and % of cells with usCA: by the MTT-test r = from 0.50 up to 0.61 (p = from 0.06 up to 0.003), but by the DCFDA-test the strength of correlation was smaller: r = from 0.38 up to 0.48. An inverse correlation was found between initial oxidative state of mononuclear cells and the frequency of CA in lymphocytes. Similarly a marked inverse correlation between degree of DNA unwinding by the ethidium bromide assay on leukocytes and sCA in lymphocytes was also noted. The feasibility of radiation-induced delayed genomic instability in vivo for humans long time after irradiation is discussed.

Chromosome Aberrations↗