Development of a location exposure matrix for ionizing radiation in extraterrestrial environments and its application in the study of mortality for U.S. astronauts
This project sought to locate articles containing data on radiation dosimetry in outer space, to use those data to create a Location Exposure Matrix (LEM) for equivalent radiation doses in extraterrestrial environments, and then apply the LEM to the study of US astronaut mortality between April 1959 and December 2012. The first part of the project consisted of a systematic review of studies that contained equivalent dose measurements for locations in outer space. The search returned 369 articles. After applying inclusion and exclusion criteria, 38 were reviewed by a radiation safety specialist and found to be of acceptable quality. The final set contained data on US spacecraft and the Russian Mir Space Station. The data from the dosimetry articles allowed for estimates of equivalent dose rate for 14 locations in low Earth orbit (LEO) defined by orbital inclination, altitude, and spacecraft. The dose estimates in the LEM were calculated as micro-Sievert per hour (&mgr;Sv/hr) and ranged from a low of 3.5 &mgr;Sv/hr onboard the Space Shuttle to a high of 80.2&mgr;Sv/hr during extravehicular activity (EVA). The greatest exposures were, in general, at higher inclinations and at higher altitudes within inclinations, and those from EVA were greater than those from inside spacecraft. Data from the LEM were then used to estimate cumulative equivalent radiation doses for 330 US astronauts between April 1959 and December 2012. The astronauts accrued 8,232.7 person-years of follow-up and a total estimated equivalent radiation dose of 7,601.8 mSv in that period. Age-adjusted models provided no evidence of an increase in cancer mortality risk or mortality risk from all natural causes due to being at or above the median of total equivalent radiation dose. This work serves both as an update to earlier work on astronaut mortality and as a demonstration project of how to better use the wealth of radiation data available in the peer reviewed literature. Because low statistical power, insufficient dose, insufficient latency, and exposure misclassification may be masking a relationship between ionizing radiation and mortality risk, it is advised that periodic follow-ups be performed, especially among astronauts with the largest total doses. It is hoped that this work can be expanded in the near future, and that it may serve as a template for similar work with other routine exposures faced by astronauts as humans continue to explore the solar system.
Reynolds, Robert J, "Development of a location exposure matrix for ionizing radiation in extraterrestrial environments and its application in the study of mortality for U.S. astronauts" (2013). Texas Medical Center Dissertations (via ProQuest). AAI3604553.