Last Published:  07/30/21 01:05:31 PM (Central)
Responsible Element: Space Radiation (SR)
Status: Open
Description

The current NASA radiation cancer risk projection model estimates the risk of radiation carcinogenesis based on human epidemiological data and is dependent on crew sex, age at exposure, and attained age. Analysis of radiation-exposed human cohorts indicates tissue-specific sensitivity to radiation-associated carcinogenesis with some tissues contributing more to overall risk estimates than others. However, epidemiological analysis has been performed on datasets in which the radiation exposure, total dose, dose-rate, and type of radiation differs from the space radiation environment. Additionally, these epidemiological cohorts do not represent the astronaut population who are healthy workers, generally non-smokers, and whose level of fitness is beyond that of the general population.

Differential gene expression and epigenetic differences contribute greatly to tissue specific carcinogenesis risk, however the risk is not uniform across organs. The current NASA model calculates excess lifetime cancer risk due to radiation exposure using a never-smoker US population to represent the astronaut cohort. Because radiation-associated cancer risk is dependent on cancer mortality and incidence rates in the representative population, the selection of this population impacts the tissue-specific and overall cancer risk estimates. Further, how excess risk models (excess absolute risk – EAR, or excess relative risk – ERR) are weighted for each tissue and applied to the representative population also impacts tissue-specific excess risk estimates. Therefore, research is necessary to identify, quantify, verify, and translate the contributions of tissue-specific radiation sensitivity to overall cancer risk and determine if major sex-specific differences exist in the context of cancer risk from space radiation exposure.

Approach

Epidemiological analysis and expert evidence review of available human studies to assess tissue-specific cancer risk and update lifetime risk projection. Ground-based research using appropriate in vitro and in vivo models to identify and quantify tissue-specific radiation-associated cancer risks and translate and verify findings from epidemiological data sets. Comparative studies of both sexes will be required as well as studies of sex-specific organs, such as prostate and breast, to adequately describe sex dependence in risk assessments. Assessment of cancer outcomes in relevant comparison populations.  

Target for Closure
  • Identification of biological models to assess the role of tissue sensitivity in space radiation carcinogenesis and refine risk assessment models.

  •  Estimates of tissues-specific contribution to overall radiation-cancer risk following space radiation exposure based on biological models and relevant epidemiological cohorts.

  •  Recommendations for tissue-specific radiation risk coefficients and associated risk transfer weights based on epidemiological analysis that can be implemented into risk assessment model.

  •  Verification of findings from epidemiological studies using biological models.

  •  Recommendations for use of appropriate representative populations in assessing lifetime risk in an astronaut population.

Mappings
Risk Risk of Radiation Carcinogenesis
You are here! Gap Cancer-203: Evaluate the tissue-specific risks of space radiation exposure on cancer outcomes.
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