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13 Summary and Research Needs
Pages 313-324

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From page 313...
... evaluated with respect to the cellular mechanisms involved. In vitro data on the introduction of gene mutations by low- For animal models of radiation carcinogenesis that are deLET ionizing radiation are consistent with knowledge of pendent on cell killing, there tend to be threshold-like doseDNA damage response mechanisms and imply a non- responses and high values of DDREF; therefore, less weight threshold low-dose response for mutations involved in was placed on these data.
From page 314...
... At this time, the assumption that any stimulating Consideration of Phenomena That Might Affect Risk effects from low doses of ionizing radiation will have a sigEstimates for Carcinogenesis at Very Low Doses nificant effect in reducing long-term deleterious effects of A number of biological phenomena that could conceiv- radiation on humans is unwarranted. ably affect risk estimates at very low radiation doses have been reported.
From page 315...
... A further though examples of apparent stimulatory or protective ef- conclusion was that there is little evidence of specific tumorifects can be found in cellular and animal biology, the pre- genic signatures of radiation causation, but rather that radiaponderance of available experimental information does not tion-induced tumors develop in a tumor-specific multistage support the contention that low levels of ionizing radiation manner that parallels that of tumors arising spontaneously. have a beneficial effect.
From page 316...
... The DD, therefore, provides a conve in DNA damage response and tumor-suppressor-type genes nient yardstick to express risks and a perspective of whether can serve to elevate radiation cancer risk. the predicted increases are trivial, small, or substantial rela Limited epidemiologic data from follow-up of second tive to the baseline.
From page 317...
... atomic bombings in Hiroshima and Nagasaki continues to Risk estimates have been made only for the first two post- serve as a major source of information for evaluating health irradiation generations. The population genetic theory of risks from exposure to ionizing radiation, and particularly equilibrium between mutation and selection (i.e., the equi- for developing quantitative estimates of risk.
From page 318...
... age 60) for atomic bomb survivors with doses in each of 10 lines are approximate 95% confidence intervals.
From page 319...
... The excess risks Ideally, where population-based cancer registries do appear to be higher in populations of women treated for not exist to establish cohorts of cancer survivors, benign breast conditions, suggesting that these women may hospital-based registries can be established to identify be at an elevated risk of radiation-induced breast cancer. The cohorts of exposed patients whose mortality and morhemangioma cohorts showed lower risks, suggesting a pos- bidity can be followed.
From page 320...
... Risk estimates from these studies are gene-radiation interactions that may render particular variable, ranging from no risk to risks an order of magnitude subsets of the population more sensitive to radiation- or more than those seen in atomic bomb survivors. induced cancer.
From page 321...
... follow-up -- of these workers, as they enter an age Ecologic studies of persons exposed to environmental range when cancer incidence and mortality rates in- sources of ionizing radiation have not been useful in devel crease, will provide useful improvements of the direct oping risk estimates. Exposure levels are low, the studies cancer risk estimates drawn from these studies of relate to exposure of populations rather than individuals, and exposure to low-dose, low-LET radiation.
From page 322...
... of risk estimates based on Japanese atomic bomb survivors · Genetic variation in the population is a potentially im- to use in estimating risks for the U.S. population.
From page 323...
... Epidemiologic studies in general uncertainty in the factor used to adjust risk estimates for ex Data from the LSS should be supplemented with posure at low doses and low dose rates, and uncertainty in data on populations exposed to low doses and/or low the method of transport. Additional sources of uncertainty dose rates, especially those with large enough doses to would increase the width of these intervals.


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