Last Published:  11/23/20 11:55:10 AM (Central)
Responsible Element: Space Radiation (SR)
Status: Open

The uncertainties in how low-dose-rate exposures to particle radiation affect the risk of radiation-associated health outcomes are a major contributor to overall uncertainty in risk estimates. Current risk estimates are primarily based on human epidemiological evidence from the Life Span Study of atomic bomb survivors who experienced a single, acute dose of radiation composed primarily of gamma rays with a contribution from neutrons. However, astronauts will be exposed to a chronic low-dose space radiation environment. Therefore, risk estimates from acute exposures are scaled using a dose and dose-rate effectiveness factor (DDREF) to reflect the chronic nature of space radiation. The current NASA model applies a central estimate for the DDREF of 1.5 to solid cancer risk estimates that was selected based on the BEIR VII report, which assessed terrestrial human epidemiology data and animal data. The uncertainty distribution around the central estimate (95% CI: 0.83 to 2.67) is based on terrestrial human epidemiological data, animal data, and cellular data. Both relative increases and decreases in carcinogenesis-related outcomes have been correlated with changes in dose-rate, dependent on examined endpoints, radiation type, and total dose. Additionally, the interaction between radiation quality, total dose and dose-rate has not been fully established. Limited human epidemiological data is available that may provide a more relevant description of the effects of the chronic or protracted low dose-rate exposures in the context of astronaut risk. It is important to note that particle radiation does not deliver dose at a low dose-rate in a conventional context because particles deposit energy as discrete, clustered ionization events. Historical technological limitations in ground-based accelerator design and capability have largely limited the generation of large experimental data sets that address dose-rate effects for particle exposures. Additionally, no data currently exists to provide understanding for the role of dose-rate in a mixed particle radiation field similar to that in space. Therefore, more data is necessary to characterize the role of dose-rate in radiation carcinogenesis for chronic space radiation exposures.

Ground-based research using appropriate in vitro and in vivo models to acquire the necessary data sets for accurate estimation of dose-rate effects for heavy ions and mixed field exposures. NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory (BNL) supports multiple ion and mixed field studies with fast ion switching for more complex mixed-field GCR simulations. Analysis and synthesis of data from relevant human epidemiological cohorts. Additional approaches also include advanced biostatistical methods to combine past, current, and future research results into data-driven models.

Target for Closure
  • Characterization and quantification of the impact of dose-rate on radiation-associated cancer risk relevant to the chronic space radiation environment.
  • Data-driven models of dose-rate effects that can be implemented to scale epidemiological excess cancer risk estimates to the space radiation environment.
Risk Risk of Radiation Carcinogenesis
You are here! Gap Cancer-201: Determine the role of dose-rate in space radiation-induced carcinogenesis.

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