A SINGLE therapeutic dose of radiation can trigger dangerous amounts of bone loss, leaving bones hollowed out and frail 鈥� at least in mice. The finding has implications for cancer radiation therapies, but reports that the findings bode ill for astronauts on long space missions may be overstating the danger.
Ted Bateman and his colleagues at Clemson University in South Carolina analysed the bones of mice exposed to four kinds of radiation: gamma rays, protons, and high-speed carbon and iron nuclei. They created 3D computer scans of the spongy interior of the bones, and used these to calculate how much bone the irradiated mice lost relative to a control group.
In each case, the irradiated mice lost between 29 and 39 per cent of the bones鈥� spongy interior, which acts as a latticework to strengthen bones. 鈥淲e were surprised at how large the difference in bone mass was,鈥� says Bateman.
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The dose for each of the radiation types was 2 gray, which is comparable to a single dose of radiation therapy. Over a full course of such therapy, a patient may receive a total dose as high as 70 gray. Patients often suffer bone loss and are at a greater risk of fractures, but it was not clear until now that even a single dose of radiation can trigger bone loss, because cancer itself can reduce bone mass, as can the chemotherapy that often accompanies radiation therapy (Journal of Applied Physiology, DOI: 10.1152/japplphysiol.01078.2005).
However, extrapolating the results to people is a tricky business, says Bateman, in part because the mice鈥檚 bones were still growing, making them more susceptible to radiation.
Interpreting what this research means for human space flight is also tricky. Frank Cucinotta, NASA鈥檚 chief radiation health officer, is not convinced that there is cause for concern. He points out that the dose in the mouse experiments was 40 times what space station astronauts experience over a period of months, and 2 to 4 times what astronauts on a Mars mission would endure.
鈥淚rradiated mice lost between 29 and 39 per cent of the bones鈥� spongy interior, which acts as a lattice to strengthen bones鈥�
Previous studies by the International Atomic Energy Agency that looked at the medical histories of nuclear power plant technicians and radiologists, who receive long-term exposure to astronaut-like doses of gamma radiation, showed no increased risk of bone fractures. However, astronauts are also exposed to high-energy protons and iron nuclei, which in Bateman鈥檚 study caused a similar amount of bone loss as gamma rays. That implies astronauts should suffer no more bone loss from other kinds of radiation than the people in the IAEA study, Cucinotta says.
