ADAPTIVE BIOLOGICAL RESPONSES FOLLOWING EXPOSURES TO IONIZING RADIATION
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2007-31-03
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Dose-Response, vol 5, no 1, Cover
(2007-03-01)
Dose-Response, vol 5, no 1, Front Matter
(2007-03-01)
Dose-Response, vol 5, no 1, Table of Contents
(2007-03-01)
LOW DOSES OF RADIATION REDUCE RISK IN VIVO
(2007-03-01) Mitchel, REJ
The “Linear No Threshold” hypothesis, used in all radiation protection practices, assumes that all doses, no matter how low, increase the risk of cancer, birth defects and heritable mutations. In vitro cell based experiments show adaptive processes in response to low doses and dose rates of low LET radiation, and do not support the hypothesis. This talk will present cellular data and data from animal experiments that test the hypothesis in vivo for cancer risk. The data show that a single, low, whole body dose (less than about 100 mGy) of low LET radiation, given at low dose rate, increased cancer latency and consequently reduced both spontaneous and radiation-induced cancer risk in both genetically normal and cancer-prone mice. This adaptive response lasted for the entire lifespan of all the animals that developed these tumors, and effectively restored a portion of the life that would have been lost due to the cancer in the absence of the low dose. Overall, the results demonstrate that the assumption of a linear increase in risk with increasing dose in vivo is not warranted, and that low doses actually reduce risk.
DOE PROGRAM—DEVELOPING A SCIENTIFIC BASIS FOR RESPONSES TO LOW-DOSE EXPOSURES: IMPACT ON DOSE-RESPONSE RELATIONSHIPS
(2007-03-01) Brooks, Antone L; Couch, Lezlie
The DOE Low Dose Radiation Research Program focuses on biological mechanisms involved in response to low doses of both low and high-LET radiation (<0.1Gy). This research program represents a merging of new technologies with cutting edge biological techniques associated with genomics. This merger enables observation of radiationinduced cellular and molecular changes previously undetectable. These low-dose responses define mechanisms of interaction of radiation with living systems, and characterize the shape of dose-response. The research from this program suggests radiation paradigms regarding the involvement of radiation in the carcinogenic process. New biological phenomena observed at low doses include initial radiation-induced DNA damage and repair, changes in gene expression, adaptive responses and bystander effects. However, information from this cellular-molecular level cannot be directly extrapolated to risks in human populations. Links must be carefully developed between dose-response relationships at the cell and tissue levels and risk to human populations. The challenge and the ultimate goal of the Program is to determine if basic scientific data can be combined with more traditional epidemiological methods to improve the estimation of radiation risk from low level radiation exposures.