Hedvig Hricak, Chair of the Department of Radiology, and medical physicist Lawrence Dauer.
Hedvig Hricak and Lawrence Dauer have been helping the National Aeronautics and Space Administration (NASA) break down an extraterrestrial “glass ceiling.”
The Memorial Sloan Kettering radiation experts were contributors to a new report that endorses NASA’s plans to adopt a universal, dose-based limit for spaceflight-induced radiation exposure that would apply to all astronauts — regardless of age or gender. This universal standard would create greater equality of opportunity for spaceflight, especially for women, notes Dr. Hricak, who chaired the US National Academies of Sciences, Engineering, and Medicine (NASEM) committee that wrote the report.
NASA currently limits astronauts’ career exposure to spaceflight radiation based on how much it raises their individual risk of death from cancer, factoring in age and gender. The risk is generally estimated to be much higher for women than for men.
“As a result, women typically have been allowed drastically smaller amounts of time in space than men,” explains Dr. Hricak. For example, the permitted length of a mission to the International Space Station could be more than 200 days for a male astronaut but less than 50 days for a female.
“The existing standard was partly shaped by decades-old studies that looked at survivors of the Hiroshima and Nagasaki atomic bombings, which exposed victims to a one-time, acute dose of radiation,” says Dr. Hricak. “The atomic bomb survival studies found women were three times more likely than men to be diagnosed with lung cancer.”
“Science has evolved — we have an enhanced understanding of radiation toxicity, and we cannot make a comparison between a single acute high-energy exposure versus chronic exposure. The environment is different, health conditions are different. There are so many factors that are different,” she adds.
NASA’s keen interest in long crewed missions to the moon and Mars prompted the agency to propose the new standard and ask NASEM to review it.
The new proposal is based on a space mission’s most vulnerable population — 35-year-old women — and caps occupational radiation exposure at below 600 millisieverts (mSV). For perspective, Americans are exposed to an average of 3 mSV of background radiation per year, says Dr. Dauer.
Space agencies from Canada, Russia, and Europe have set their astronauts’ career dose limits at 1,000 mSV. NASA’s proposed limit of 600 mSV may seem conservative by comparison, but there remain many unknowns about solar particle events and galactic cosmic rays — all of which are effects of space radiation, explains Dr. Dauer.
In addition to endorsing the proposed new radiation standard, the NASEM report advises NASA on how to more clearly communicate individual cancer risks to astronauts so they can make informed choices.
“We drew from deep medical knowledge to help shape this report,” explains Dr. Dauer. “Our expertise with medical radiation — particularly with CT scans — and how we talk to MSK patients about their concerns with radiation exposure, all contributed to this report.”
