44 research outputs found
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Experimental radiation carcinogenesis: what have we learned
The author reviews the need for animal experiments in development of a biological model for radioinduced carcinogenesis. He concludes they are vital for: (1) study of mechanisms; (2) establishment of generalizations; (3) elucidation of dose-response and time-dose relationships; and (4) determination of dose-distributions and their results, particularly for radionuclides. (PSB
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Relevance of experimental animal studies to the human experience
Animal experiments are being used to examine a number of physical and biological factors that influence risk estimations though not usually in coordination with epidemiologists. It is clear that the different mechanisms involved in different types of tumors are reflected in the diversity of dose-response relationships. The forms of the dose-response relationships are influenced by both the initial events and their expression. Evidence is accumulating that many initiated cells do not get expressed as overt cancers and host factors may play a major role in the expression of potential tumor cells. There is a need for information about the relationship of the natural incidence and susceptibility to radiation induction for more tumor types. Such experiments will help answer the question of which risk estimate models are appropriate for different tumor types and can be carried out on animals. Perhaps because of the importance of host factors risk estimates as a percentage of the natural incidence appear to be similar for human beings and mice for a small number of tumor types. The elucidation of the mechanisms involved in different tissues while a slow business remains an important role of animal experiments
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Radiation protection guidelines for space missions
The original recommendations for radiation protection guidelines were made by the National Academy of Sciences in 1970. Since that time the US crews have become more diverse in their makeup and much has been learned about both radiation-induced cancer and other late effects. While far from adequate there is now some understanding of the risks that high-Z and -energy (HZE) particles pose. For these reasons it was time to reconsider the radiation protection guidelines for space workers. This task was undertaken recently by National Council on Radiation Protection (NCRP). 42 refs., 2 figs., 9 tabs
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Mice, myths, and men
The author discusses some examples of how different experimental animal systems have helped to answer questions about the effects of radiation, in particular, carcinogenesis, and to indicate how the new experimental model systems promise an even more exciting future. Entwined in these themes will be observations about susceptibility and extrapolation across species. The hope of developing acceptable methods of extrapolation of estimates of the risk of radiogenic cancer increases as molecular biology reveals the trail of remarkable similarities in the genetic control of many functions common to many species. A major concern about even attempting to extrapolate estimates of risks of radiation-induced cancer across species has been that the mechanisms of carcinogenesis were so different among different species that it would negate the validity of extrapolation. The more that has become known about the genes involved in cancer, especially those related to the initial events in carcinogenesis, the more have the reasons for considering methods of extrapolation across species increased
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Radiation carcinogenesis: radioprotectors and photosensitizers
This paper outlines 1) some of the salient features of radiation carcinogenesis that are pertinent to the questions of how the carcinogenic effects might be influenced, 2) the effects of radioprotectors on ionizing radiation-induced cancer, and 3) the effect of photosensitizers on UVR-induced skin cancer
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Approaches to radiation guidelines for space travel
There are obvious risks in space travel that have loomed larger than any risk from radiation. Nevertheless, NASA has maintained a radiation program that has involved maintenance of records of radiation exposure, and planning so that the astronauts' exposures are kept as low as possible, and not just within the current guidelines. These guidelines are being reexamined currently by NCRP Committee 75 because new information is available, for example, risk estimates for radiation-induced cancer and about the effects of HZE particles. Furthermore, no estimates of risk or recommendations were made for women in 1970 and must now be considered. The current career limit is 400 rem. The appropriateness of this limit and its basis are being examined as well as the limits for specific organs. There is now considerably more information about age-dependency for radiation and this will be taken into account. Work has been carried out on the so-called microlesions caused by HZE particles and on the relative carcinogenic effect of heavy ions, including iron. A remaining question is whether the fluence of HZE particles could reach levels of concern in missions under consideration. Finally, it is the intention of the committee to indicate clearly the areas requiring further research. 21 references, 1 figure, 7 tables
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Report on NCI symposium: comparison of mechanisms of carcinogenesis by radiation and chemical agents. II. Cellular and animal models
The point at which the common final pathway for induction of cancer by chemical carcinogens and ionizing radiation has not been identified. Although common molecular targets are suggested by recent findings about the role of oncogenes, the mechanism by which the deposition of radiation energy and the formation of adducts or other DNA lesions induced by chemicals affects the changes in the relevant targets may be quite different. The damage to DNA that plays no part in the transformation events, but that influences the stability of the genome, and therefore, the probability of subsequent changes that influence tumorigenesis may be more readily induced by some agents than others. Similarly, the degree of cytotoxic effects that disrupt tissue integrity and increase the probability of expression of initiated cells may be dependent on the type of carcinogen. Also, evidence was presented that repair of the initial lesions could be demonstrated after exposure to low-LET radiation but not after exposure to chemical carcinogens
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Risk assessment and late effects of radiation in low-earth orbits
The radiation dose rates in low-earth orbits are dependent on the altitude and orbital inclination. The doses to which the crews of space vehicles are exposed is governed by the duration of the mission and the shielding, and in low-earth orbit missions protons are the dominant particles encountered. The risk of concern with the low dose rates and the relatively low total doses of radiation that will be incurred on the space station is excess cancer. The National Council on Radiation Protection and Measurements has recently recommended career dose-equivalent limits that take into account sex and age. The new recommendations for career limits range from 1.0 Sv to 4 Sv, depending on sex and on the age at the time of their first space mission, compared to a single career limit of 4.0 Sv previously used by NASA. Risk estimates for radiated-induced cancer are evolving and changes in the current guidance may be required in the next few years. 10 refs., 1 fig., 3 tabs
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Radiation effects in space
The paper discusses the radiation environment in space that astronauts are likely to be exposed to. Emphasis is on proton and HZE particle effects. Recommendations for radiation protection guidelines are presented. (ACR
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Radiation protection guidelines for the skin
With the exception of the function of cells in the skin associated with immunocompetence nonstochastic effects have been well characterized and threshold doses are known with a precision appropriate for setting radiation protection standards. A dose limitation of 0.5 Sv per year and a working lifetime dose limit of 20 Sv should protect the worker population adequately and therefore, the current protection standards are quite adequate. The risk estimate for skin cancer is very dependent on the selection of the projection model and on the mortality rate assumed. Based on the relative risk model, a mortality rate of 0.2% and summing risks for both UVR exposed and shielded skin the risk is about twice (1.94/10{sup {minus}4} Sv{sup {minus}1}) that which ICRP derived in 1977. With the absolute model the risk is considerably less, about 0.5/10{sup {minus}4} Sv{sup {minus}1}. 47 refs., 3 figs., 1 tab