UPTON, NY - It doesn't just matter how much radiation an astronaut is exposed to, time and the order in which charged particles strike human cells are important factors as well. That's the main finding of a study simulating radiation exposure conducted at the U.S. Department of Energy's Brookhaven National Laboratory and published in the September 2006 edition of Radiation Research. In the study, human cells were three times more likely to develop properties similar to those in the initial stages of cancer when they were exposed to two types of high-energy particles in a short period of time.
The radiation field in space contains high levels of high-energy protons and much lower levels of high atomic number, high-energy (HZE) particles such as iron and titanium.
"Most people studying the effects of space radiation have looked at the effects of just one type of particle, either the protons or the HZE particles," said Brookhaven biologist Betsy Sutherland, the paper's lead author. "This is one of the first studies to try to imitate real space radiation conditions closely, where, on average, a cell will be hit by a proton first and then by an HZE particle. We decided to examine what this does to human cells."
To test the effect of dual-particle irradiation, Sutherland's team at the NASA Space Radiation Laboratory, a facility built at Brookhaven Lab specifically for space radiation studies, first exposed normal human cells to a beam of protons. Then, anywhere from 2.5 minutes to 48 hours later, they exposed the cells to iron or titanium particles. After
allowing the cells to grow, the researchers counted the number of cells that survived to form colonies and those that acquired the ability to grow without being affixed to a solid surface. This characteristic, known as anchorage-independent growth, is an early indicator that these cells might be on the pathway to cancer.