This Master project looked at the Excess Relative Risk per unit of effective dose (ERR/mSv) of cancer mortality in four different cohorts exposed to ionizing-radiation along with a pooled analysis that accounts for inter-study variability.
It investigated the potential sex-differences in the risks of cancer mortality associated with ionizing radiation, particularly in the context of growing space exploration ambitions laid out by various governmental and private companies. Ionizing-radiation health effects data remains very limited and radiation effects are still under investigation. Ionizing radiation data pertaining to terrestrial exposures was used to estimate corresponding space-risks, assuming that the biological effects would be similar enough. To better understand those risks, mean external dose and SMR for cancer from four different epidemiological cohorts with terrestrial exposures were extracted from publications and converted to ERR/mSv.
Data from male and female populations of each cohort were separately extracted when available and compared using meta-analytic methods. This project made use of a random- effects meta-analysis model to account for inter-study variability across the different cohorts and derived a pooled-ERR/mSv based on all individual cohort risks, called “Pooled”. Python and its libraries were used to code forest-plots from the gathered data to better visualize results from the analysis. Results indicate the point estimates for females tend to be higher than for males, suggesting that females might have a higher ERR/mSv compared to males. Although not statistically significant, these results emphasize the need for more research into sex-specific considerations in space travel. The limitations of this project make it challenging to provide a definite assessment, as space radiation exposures greatly differ from the types of exposures received on Earth and sex-segregated data is not widely available from existing cohorts. Female-centric analyses in occupational or low-dose radiation studies are often limited by the small sample size of female subjects. This is also seen here where all cohorts are comprised of mostly male subjects.
However, this work pinpoints the current knowledge gap in providing evidence of ionizing- radiation sex-dependent effects and encourages further research on this topic. A bigger data pool, specifically regarding female data, is needed to hopefully generate risk and dosimetry models in the future that could better extrapolate to the radiation risk related to exposures in space.