Radiation Hazards to Crews of Interplanetary Missions Biological Issues and Research Strategies (1996) / Chapter Skim
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4: Priority Research Questions and Strategies
4: Priority Research Questions and Strategies
Pages 42-54
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From page 42... ...
For types of radiation with differing LET the dose is converted to a dose equivalent in sieverts and the risk calculated as above. However, the proper conversion factors for HZE particles and the products they generate in passing through shielding are poorly known at present, as chapters above emphasize.
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From page 43... ...
First, can the risk due to irradiation by protons in the energy range of the space environment be predicted on the basis of the risk posed by exposure to low-LET radiation; i.e., is it appropriate to assume that the quality factor is 1, and is there evidence for repair of damage in cells following fractionated exposure to protons and HZE particles? Second, what are the appropriate quality factors for making risk calculations with respect to HZE particles?
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From page 44... ...
The task group recommends that bone marrow cells and peripheral lymphocytes, which are easily analyzed cytogenetically, be analyzed for chromosomal aberrations. Based on the information obtained in these cytogenetic studies, it would then be feasible to design a study to assess induction of leukemia and breast cancer in mice exposed, behind shielding, to acute doses of HZE particle radiation incident on the shielding if it appears necessary from the cellular studies.
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From page 45... ...
Question 3: Are there studies that can be conducted to increase the confidence of extrapolation from rodents to humans of radiation-induced genetic alterations that in turn could enhance similar extrapolations for cancer? The studies recommended for addressing question 2 would give relative sensitivity factors for mutations, chromosomal aberrations, and cell killing in rodent and human cells in vitro, and the in vivo cytogenetic studies would allow comparison of in vitro and in vivo responses in a single species, most likely the mouse.
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From page 46... ...
Reductions in the uncertainties in the values of the specific input quantities have differing effects on the magnitude of the uncertainty of the total risk, depending on the method chosen. For example, in the conventional approach, the squares of the fractional uncertainties in the absolute physical doses and in the quality factors will contribute additively to the total uncertainty irrespective of the absolute values of the two quantities if they are two independent quantities.
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From page 47... ...
Current knowledge of the fragmentation products produced by HZE particles is limited to only a few particles in a few materials. For knowledgeable shielding design, the initial radiation fields, the reaction probabilities, and the secondary particles produced as a function of angle must be determined through physical measurements, at a HZE particle accelerator, of the particle types and energies resulting behind different compositions and thicknesses of shielding.
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From page 48... ...
Ideally, the studies should include the effects of repeated exposure to protons and heavy ions at low fluences. However, protracted exposure to gamma rays may be the most practical approach, and gamma rays should be an adequate surrogate for protons.
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From page 49... ...
These studies would require access to appropriate facilities for irradiation with HZE particles. Under current conditions (2 weeks' available beam time per year)
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From page 50... ...
The task group recommends that, if the goal of safe interplanetary missions with human crews is sought, NASA explore various possibilities, including the construction of new facilities, to increase the research time available for experiments with HZE particles.
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From page 51... ...
In both figures, the bottom axis indicates the estimated amount of time required to carry out the various strategies; the top axis indicates the general dependence of the mission time line on the research. Strategies that can be carried out independently are separated by dotted lines.
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From page 53... ...
PRIORITY RESEARCH QUESTIONS AND STRATEGIES 53 Ct ·Ct Cal o sly ;^ no rim o o ~ _ _I Ct ·_.
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From page 54... ...
1987. Effects of heavy ions on rabbit tissues: Induction of DNA strand breaks in retinal photoreceptor cells by high doses of radiation.
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