Radiation Hazards to Crews of Interplanetary Missions Biological Issues and Research Strategies (1996) / Chapter Skim
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1: Introduction
1: Introduction
Pages 5-12
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From page 5... ...
The last concern is a serious one because the levels of radiation in space are high enough and the missions are long enough that adequate shielding is necessary to minimize carcinogenic, cataractogenic, and possible necrologic effects for crew members. A question still to be answered is what will provide the necessary protection, for the extent of a mission, against the biological effects of high-energy galactic cosmic ray particles ranging from energetic protons with low mean linear energy transfer (LET)
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From page 6... ...
This dose reduction, in going from acute to chronic exposure, also depends on the biological system and may range from a factor of 2 to 10.4 The dose rate reduction factor for HZE particles is not well known but is probably closer to 1.5 Two other factors that must be considered, but whose impacts are currently unknown, are the effects of biochemical or cellular repair reactions following exposure to HZE particles and the effects of microgravity on such reactions. Thus, in estimating the risks to humans exposed to radiation in space, the uncertain factors are the radiation fields behind the shielding and the extrapolation, via cell culture and animal experiments, from the uncertain risks posed by acute low-LET exposure to risks posed by chronic high-LET exposure.
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From page 7... ...
recommend research programs required to fill gaps representing deficiencies in current knowledge relative to accomplishment of the above objectives. The panel's report, Radiobiological Factors in Manned Space Flight, was published in 1967 and still remains an essential reference.8 It was the main source of information for the guidelines recommended in 1970 by the NRC to NASA9 for establishing radiation exposure limits for space crew members.
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From page 8... ...
Effects Induced by Protons While the estimated risks of adverse biological effects calculated from the data on atomic bomb survivors are the basis for current radiation protection limits, the types of radiation received by the atomic bomb survivors differ markedly from the types of radiation to which space crews would potentially be exposed. In deep space, the radiation environment consists mainly of galactic cosmic radiation (OCR)
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From page 9... ...
Although the work of Lett and coworkers and of Worgul and coworkers suggests that it may be possible, with further data, to extrapolate across species to obtain RBE values for cataract induction, current data do not allow reliable estimation of the risk of cataract induction occurring in humans as a result of exposure to radiation in deep space.36 37 Observations on radiotherapy patients indicate that very high doses of low-LET radiation give rise to deterministic-type damage. HZE particles produce high-dose ionization tracks and kill the cells they traverse.
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From page 10... ...
It is agreed that the RBE for carcinogenesis increases with the increasing LET of the radiation. The evidence comes largely from animal experiments with fission neutrons but also from data on induction of lung tumors in humans exposed to alpha particles from radon.38 There has been only one systematic study of the relationship between the LET of heavy ions and the RBE values of the ions for tumor induction, which was carried out on the Harderian gland of mice.39 Although this gland is a suitable epithelial system, it is the only tumor model that has been examined over the range of LET values encountered in space.
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From page 11... ...
1957. The relative biological effectiveness of various ionizing radiations in mammalian systems.
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From page 12... ...
1994. Fluence-based relative biological effectiveness for charged particle carcinogenesis in mouse harderian gland.
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