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

The current NASA radiation cancer risk projection model estimate the risk of radiation carcinogenesis is based on human epidemiological data and analysis 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. Furthermore, epidemiology has identified sex-dependent differences in radiation-associated cancer risk estimates with females having a higher lifetime risk compared to males that is largely based on tissue-specific contributions from the lung. Breast and ovarian cancers make further contributions to increased excess lifetime risk in females compared to males. 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. The current NASA model calculates excess lifetime cancer risk due to radiation exposure using a never-smoker US to represent the astronaut population. 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 (EAR or ERR) are weighted for each tissue and applied to the representative population also impact 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 space radiation exposure.

Approach 
Epidemiological analysis and expert evidence review of available human studies to assess tissue-specific and sex-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 and sex-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 tissue sensitivity and sex differences 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 and sex-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 representative populations to use in assessing lifetime risk in an astronaut population
Mappings
Risk Risk of Radiation Carcinogenesis
You are here! Gap Cancer-301: Determine the tissue-specific contributions to overall space radiation carcinogenic risk and whether there are sex-specific dependencies.
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