Comparative Dosimetry of Radon in Mines and Homes (1991) / Chapter Skim
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Other Considerations
Other Considerations
Pages 52-59
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From page 52... ...
The second of these components is discussed in the BEIR IV report (NRC, 1988) and this chapter as it is a major source of uncertainty in extrapolating risks due to radon and its decay products.
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From page 53... ...
Heightened cell proliferation may also reflect a state of tissue injury that may facilitate the outgrowth of transformed cells into tumors, but the proliferation per se may not be the proximate cause of the enhanced clonal expansion of transformed cells. The importance of tissue factors on tumor formation has been shown in experiments that demonstrate the presence of a large number of transformed cells in the carcinogen-treated rat tracheal epithelium under conditions that produce few tumors (Terzaghi, 19791; also, neoplastic transformants have been shown to be nontumorigenic when used, together with normal cells, to repopulate the denuded tracheal epithelium (Terzaghi-Howe, 1987~.
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From page 54... ...
Cells that are held in a confluent state in tissue culture, with very little cell proliferation, rapidly repair tumorigenic damage caused by low-LET radiation (Borek and Sachs, 1968~; in contrast, alpha-particle irradiation of confluent cells in culture shows no evidence of such repair (Robertson et al., 19831. Reversal of the tumorigenic effect of low-LET radiation, ranging from 0.1 to 10 keV/,~bm, in the rat skin with dose fractionation has a half-life of several hours and eventually reaches about 90% completion; the time pattern is about the same as that in tissue culture and may correspond to the repair of chromosomal breaks (Bums and Albert, 1986; Burns et al., 1979~.
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From page 55... ...
The BEIR IV committee's examination of the miners experience indicates that the tumorigenic effect of radon exposure fades with time after the exposure is discontinued (NRC, 1988~. Nevertheless, uncertainty remains concerning the effects of dose rate and duration of exposure at very low levels of exposure.
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From page 56... ...
Lung tumor induction by plutonium-238 appears to be much enhanced in regions of the lung where the radioactive particles cluster and produce local tissue damage (Sanders et al., 1988~. Tissue wounding or damage with its associated regeneration appears to be an exaggerated form of tissue growth, because like growth, regenerative proliferation is associated with retention of the multiplying cells, and thus, clonal expansion of neoplastically transformed cells is favored.
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From page 57... ...
The BEIR IV committee assumed a multiplicative interaction between these two factors in producing lung cancer. The committee based this decision on the weight of the evidence from the literature and on its own analysis of data from two studies of uranium miners.
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From page 58... ...
1987. Inhibition of carcinogen altered rat tracheal epithelial cell proliferation by normal epithelial cells in-vivo.
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From page 59... ...
Department of Health and Human Services, Public Health Service, Centers for Disease Control, Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health. Wehner, A
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