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  • 1995-1999  (24)
  • 1
    Electronic Resource
    Electronic Resource
    A hybrid likelihood algorithm for risk modelling (1995)
    Springer
    Radiation and environmental biophysics 34 (1995), S. 13-20 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The risk of radiation-induced cancer is assessed through the follow-up of large cohorts, such as atomic bomb survivors or underground miners who have been occupationally exposed to radon and its decay products. The models relate to the dose, age and time dependence of the excess tumour rates, and they contain parameters that are estimated in terms of maximum likelihood computations. The computations are performed with the software package EPICURE, which contains the two main options of person-by person regression or of Poisson regression with grouped data. The Poisson regression is most frequently employed, but there are certain models that require an excessive number of cells when grouped data are used. One example involves computations that account explicitly for the temporal distribution of continuous exposures, as they occur with underground miners. In past work such models had to be approximated, but it is shown here that they can be treated explicitly in a suitably reformulated person-by person computation of the likelihood. The algorithm uses the familiar partitioning of the log-likelihood into two terms,L 1 andL 0. The first term,L 1, represents the contribution of the ‘events’ (tumours). It needs to be evaluated in the usual way, but constitutes no computational problem. The second term,L 0, represents the event-free periods of observation. It is, in its usual form, unmanageable for large cohorts. However, it can be reduced to a simple form, in which the number of computational steps is independent of cohort size. The method requires less computing time and computer memory, but more importantly it leads to more stable numerical results by obviating the need for grouping the data. The algorithm may be most relevant to radiation risk modelling, but it can facilitate the modelling of failure-time data in general.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01210540
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  • 2
    Electronic Resource
    Electronic Resource
    Childhood leukemia in Belarus before and after the Chernobyl accident (1996)
    Springer
    Radiation and environmental biophysics 35 (1996), S. 75-80 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Childhood leukemia (ICD 204–208 [1]) incidence rates in the different regions of Belarus are reported for a period before and after the Chernobyl accident (1982–1994). There are, at this point, no recognizable trends towards higher rates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02434028
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  • 3
    Electronic Resource
    Electronic Resource
    Generalization of the variance-covariance method for microdosimetric measurements (1996)
    Springer
    Radiation and environmental biophysics 35 (1996), S. 111-115 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract   The variance method of microdosimetric measurements and its extension, the variance-covariance method, permit the determination of an essential parameter of radiation quality, the dose mean event size, y d . The methods have – among other advantages – the feature that they permit measurements for smaller simulated sites than the conventional single-event technique. It is, therefore, desirable to employ them also for the determination of further moments of the distribution of y. The formulae for the first three moments are here derived both for the case of constant dose rate and of fluctuating dose rates. A second article will use the same mathematical approach to deduce formulae that remain valid even if there are slow changes of the ratio of dose rates in the two detectors for the variance-covariance method. A third article will explore – in terms of microdosimetric data – the applicability of the formulae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050017
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  • 4
    Electronic Resource
    Electronic Resource
    Fallacies of numerology (1998)
    Springer
    Radiation and environmental biophysics 36 (1998), S. 215-216 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050074
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  • 5
    Electronic Resource
    Electronic Resource
    The dosimetry system DS86 and the neutron discrepancy in Hiroshima – historical review, present status, and future options (1998)
    Springer
    Radiation and environmental biophysics 37 (1998), S. 293-310 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The historical development of the dosimetry systems for Hiroshima and Nagasaki is outlined from the time immediately after the A-bomb explosions to the publication of the dosimetry system DS86 in 1987, and the present status of the so-called Hiroshima neutron discrepancy is summarized. Several long-lived radionuclides are discussed with regard to their production by neutrons from the A-bomb explosions. With the exception of 63Ni, these radionuclides have not, up to now, been measured in samples from Hiroshima and Nagasaki. Two of them, 63Ni in copper samples and 39Ar in granite samples, were predominantly produced by fast neutrons. 63Ni can be determined by accelerator mass spectrometry with a gas-filled analyzing magnet. It should be measurable, in the near future, in copper samples up to 1500 m from the hypocenter in Hiroshima. 39Ar can be measured in terms of low-level beta-counting. This should be feasible up to a distance of about 1000 m from the hypocenter. Three radionuclides, 10Be, 14C , and 59Ni, were produced predominantly by thermal neutrons with smaller fractions due to the epithermal and fast neutrons, which contribute increasingly more at larger distances from the hypocenter. State-of-the-art accelerator mass spectrometry is likely to permit the determination of 10Be close to the hypocenter and of 14C up to a distance of about 1000 m. 59Ni should be detectable up to a distance of about 1000 m in terms of accelerator mass spectrometry with a gas-filled magnet. The measurements of 10Be, 14C, 39Ar, 59Ni – and potentially of 131Xe – can be performed in the same granitic sample that was already analyzed for 36Cl, 41Ca, 60Co, 152Eu, and 154Eu. This will provide extensive information on the neutron spectrum at the specified location, and similarly complete analyses can conceivably be performed on granite samples at other locations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050131
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  • 6
    Electronic Resource
    Electronic Resource
    International radiobiology archives of long-term animal studies: structure, possible uses and potential extension (1999)
    Springer
    Radiation and environmental biophysics 38 (1999), S. 75-79 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract  Animal experiments have contributed a great deal to our information on effects and risks arising from exposure to radionuclides. This applies, in particular, to alpha-emitting radionuclides where information from man is limited to thorotrast, 224Ra and 226Ra. The late C.W. Mays was the first to suggest that animal data in conjunction with epidemiological data could allow estimates of human risks for radionuclides – predominantly from actinides – where information in man is scarce. The ’International Radiobiology Archives of Long-term Animal Studies’ were created through the combined efforts of European, American and Japanese scientists and aim to safeguard the large amount of existing data on long-term animal experiments and make them available for, among others, an improved assessment of risks from alpha-emitting radionuclides. This paper summarizes the structure of the archives and reviews their present status and future plans. It also demonstrates the extensive information available in these archives on alpha-emitting radionuclides which is suitable for further analysis. Also, the structure of the animal archives could – in a slightly modified form – accommodate the epidemiological data available on 224Ra and thorotrast and, thus, facilitate a direct comparison of data from man, dogs and rodents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050141
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  • 7
    Electronic Resource
    Electronic Resource
    Response of pig lung to irradiation with accelerated 12C-ions (1999)
    Springer
    Radiation and environmental biophysics 38 (1999), S. 185-194 
    Details
    ISSN: 1432-2099
    Keywords: Key words Normal tissue ; Minipig ; Lung ; Heavy particles ; Carbon ionsIntroduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract  The response of pig lungs to irradiation with 12C-ions was assessed in two experiments to validate the procedures for heavy ion therapy planning at the Gesellschaft für Schwerionenforschung (GSI) and to explore their range of applicability. In both experiments, the target volume (spread-out Bragg peak, SOBP) was planned to be a 4 cm long cylinder with a diameter of 4 cm. Doses in the SOBP were prescribed to be equivalent to 5×4 Gy, 5×5.5 Gy and 5×7 Gy of x-rays in the first experiment, and to 5 fractions of 7 Gy and 9 Gy in the second experiment. The lung response in the first experiment was less than expected on the basis of earlier experiments with photons. Pneumonitis reaction and chronic fibrotic changes were observed outside the prescribed high-dose region. In the second experiment, the effects were more pronounced than had been expected on the basis of the first experiment. Changes were most intense in the high-dose region, but were also seen throughout the lung along the beam channel. Moreover, significant skin reactions were observed at the beam entrance site in all animals and – less pronounced – at the beam exit site in 3 of the 6 animals. In conclusion, the complex irradiation geometry of the pig lung, the changes of body weight between the two experiments, and insufficient accounting for a change in the relative biological effectiveness (RBE) computation led to substantial deviations of the observed reactions from expectations, the reasons for which could be identified in a subsequent analysis. The less pronounced lung reaction in the first experiment was due to an overestimation of RBE in a preliminary version of the algorithm for its determination. The extension of the fibrotic reaction resulted from the smear-out of the high-dose region due to density variations in tissue structures, respiratory movement, and limited positioning accuracy. The skin reactions at the entrance port reflect the different treatment geometry in the two experiments. The one unexplained observation is the mild skin reaction that was observed in the second experiment at the beam exit site.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050154
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of wire eccentricity on the performance of cylindrical proportional counters (1995)
    Springer
    Radiation and environmental biophysics 34 (1995), S. 245-249 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract A theoretical and experimental investigation of the influence of eccentricity of the multiplication wire on the performance of cylindrical proportional counters is presented. The electric field in the counter is calculated by the method of images, and the Townsend formalism is used to derive the gas gain. The experimental determination of detector performance is carried out with37Ar. The dependence of the gas gain and of the counter resolution on eccentricity is discussed, and it is shown that eccentricities up to 0.2 are of no concern in microdosimetric measurements with cylindrical proportional counters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01209750
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  • 9
    Electronic Resource
    Electronic Resource
    Analysis of chromosome aberrations in human peripheral lymphocytes induced by in vitro α-particle irradiation (1996)
    Springer
    Radiation and environmental biophysics 35 (1996), S. 179-184 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Irradiation of human lymphocytes by α-particles under different conditions has been seen to be substantially more effective in the induction of dicentric chromosomes than irradiation by γ-rays. However, the relative biological effectiveness (RBE) determined in these studies differed by a factor of more than 10. These variations in RBE are likely to be due in part to differing exposure conditions. Therefore, a technique designed to insure uniformity of irradiation was developed in the present study, and complications due to the cell cycle kinetics were controlled. After stimulation with phytohaemagglutinin (PHA), separated lymphocytes were allowed to attach for 3 h to the thin foil bottom of an irradiation chamber. Cell monolayers were exposed with α-particles from 241Am. Strong over-dispersion was noted for the cell-to-cell variance of the number of dicentrics. The dose response of dicentrics was linear, with a yield of 0.27 dicentrics per cell and per Gy. This corresponds to a low dose RBE of 15 relative to 137Cs γ-ray exposure under the same experimental conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/
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  • 10
    Electronic Resource
    Electronic Resource
    Postgraduate studies in radiation biology in Europe (1998)
    Springer
    Radiation and environmental biophysics 37 (1998), S. 139-142 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The present system of radiobiological research in universities and research centres is no longer able to train radiobiologists who have a comprehensive understanding of the entire field of radiation biology including both `classical' and molecular radiation biology. However, such experts are needed in view of the role radiation protection plays in our societies. No single institution in Europe could now run a 1-year, full-time course which covers all aspects of the radiobiological basis of radiation protection. Therefore, a cooperative action of several universities from different EU member states has been developed and is described herein.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050107
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