New NASA radiation standards for astronauts seen as leveling field for women

New NASA radiation standards for astronauts seen as leveling field for women

A blue-ribbon panel has endorsed NASA’s plans to revise its standard for exposing astronauts to radiation in a way that would allow women to spend more time in space.

A report by the U.S. National Academies of Sciences, Engineering, and Medicine released on 24 June encourages NASA to proceed with its plans to adopt a new standard that limits all astronauts to 600 millisieverts of radiation over their career. The current limit is the amount of radiation that correlates with a 3% increase in the risk of dying from a cancer caused by radiation exposure—a standard that favored men and older astronauts whose cancer risk from radiation was lower. The proposed standard would limit all astronauts to the allowable dosage for a 35-year-old woman.

The changes are in line with current data and puts women on an equal footing, says Hedvig Hricak, a radiologist at Memorial Sloan Kettering Cancer Center and chair of the committee that wrote the report. “There’s no evidence for significant gender difference in the radiation exposure, and associated risk of cancer,” she says.

The new standard comes as NASA gears up for renewed exploration of the Moon and, eventually, a mission to Mars. The change should remove gender from the list of factors used to decide who gets chosen for those missions, says Paul Locke, an environmental health expert at Johns Hopkins University who was not on the committee. “Women will not be penalized because they are, under the old model, at higher risk,” he says.

Whereas some experts lauded NASA’s intentions, others worry the proposal ignores the complexities and uncertainties of deep space travel. “I think they’ve pulled together the best data they have. But again, I think, more research is going to be needed,” says Albert Fornace, a radiobiologist at Georgetown University. With so few people having traveled beyond low-Earth orbit, most of the data for setting radiation exposure limits in space come from survivors of the atomic bombs in Japan and studies of people, like uranium miners, who work in conditions with high exposure to radiation. The long lead time for voyages to Mars also gives scientists time to develop ways to shield astronauts from higher levels of radiation, Fornace adds.

Francis Cucinotta, a biophysicist at the University of Nevada, Las Vegas, doesn’t agree with the report’s backing of a single dosage level. Instead, the former chief scientist for NASA’s radiation program thinks equity should come in the form of equal risk rather than equal dosages of radiation.

“[It] sounds like they’re just going to ignore the science and try to make it comfortable for everybody,” Cucinotta says, arguing that age, sex, and race affect an individual’s risk of developing cancer and should be factors when determining the amount of time astronauts can spend in space. “When they’re selected to be astronauts, there’s a lot of things where it’s not equal—it’s based on performance capability. But they’re not applying that model here.”

Cucinotta would stick with the 3% increase in the risk of dying of cancer. For a Mars mission, which is expected to expose astronauts to 1000 millisieverts, he proposes raising that maximum risk to 5% after conducting research on countermeasures and weighing genetic markers that lower an astronaut’s risk of developing cancer.

Although a mission to Mars is not planned for another decade, NASA also wants to improve how it tells astronauts about the risks. In particular, the agency proposed using a stoplight, color-coded system—using green for those at lowest risk, yellow for those with higher risk, and red for those that would exceed the lifetime radiation limit. Any astronaut on a mission expected to exceed the proposed limit would be asked to sign a waiver.

Ann Bostrom, a risk communication expert at the University of Washington, Seattle, who served on the committee, worries such a system may not be able to convey such complex information. “Sometimes if it’s too simplistic, it causes people to overlook nuances that they would otherwise see,” Bostrom says. “So [NASA] really needs to test this.”

But Scott Kelly, a former astronaut that spent nearly an entire year in space, said he values the simplicity of the traffic light system and notes that it mirrors other systems in place at NASA. “I love that thing. … That doesn’t necessarily mean it’s the best tool. But it’s one that I was very happy with,” he says.

Cucinotta and others worry astronauts don’t have the perspective to make an informed decision to accept the likely health risks of their next mission. But Kelly, who was exposed to 240 millisieverts of radiation during his 20-year career—which translates to a 1.4% increase in his risk of developing cancer—pushes back.

“There are so many factors in whether you get a fatal disease,” he says. “You’re accepting a lot of other risks by flying in space, and this one is not the biggest.”

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