One Dose of Radiation Causes 30 Percent Spongy Bone Loss
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http://www.physorg.com/news71910598.html


Mice receiving just one therapeutic dose of radiation lost up to 39%
of the spongy portion of their inner bone, reducing the inner bone’s
weight bearing connections by up to 64%, researchers reported. The
study, which appears in the online edition of the Journal of Applied
Physiology, has implications for patients receiving radiation therapy
and astronauts traveling on long space flights.

“We were really surprised at the extent of bone loss,” said lead
researcher Ted A. Bateman of Clemson University. “We’re seeing bone
loss at much lower doses of radiation than we expected.” The mice
suffered the loss of trabecular bone, the spongy area of bone inside
the dense outer area known as the cortical bone.

“It’s interesting that the trabecular bone, not the cortical bone,
suffered the damage,” said Bateman, a bioengineer who studies bone
biomechanics. The remaining spongy bone must redistribute the load to
bear the weight, but this makes the bone support structure less
efficient and leaves the bone more vulnerable to fracture.

“A murine model for bone loss from therapeutic and space-relevant
sources of radiation,” by Sarah A. Hamilton, Neil D. Travis, Jeffrey
S. Willey, Eric R. Bandstra and Ted A. Bateman, Clemson University;
and Michael J. Pecaut, Daila S. Gridley and Gregory A. Nelson, Loma
Linda University and Medical Center, appears in the online edition of
the Journal of Applied Physiology, published by The American
Physiological Society.

Mouse model applies to humans

The results of a mouse study cannot be directly applied to humans.
However, both mice and humans lose bone after radiation exposure, so
the results raise a red flag. Bateman noted that a recent clinical
study of 6,000 cancer patients reported in the Journal of the American
Medical Association found that post-menopausal women who received
pelvic radiation for cervical and colorectal cancer increased their
bone fracture risk by 60%. Radiation following anal cancer increased
the risk of fracture by 200%, he said.

Astronauts lose 2% of bone mass for each month they are exposed to the
effects of microgravity. So far, astronauts have not been exposed to
the increased radiation of outer space, but that will change when they
undertake a proposed 30-month trip to Mars, Bateman said. NASA has
focused on radiation’s cancer-causing properties and its ability to
compromise the central nervous and immune systems. But the effect on
bone health is an unexamined concern.

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The murine (mouse) model such as the one in this study provides a way
to study the physiological effects of radiation using controlled
experiments. Clinical studies of people who undergo radiation to treat
cancer are limited because of the complicating factors of the illness
itself and the chemotherapy which often accompanies it. “You can’t
study this in people, so having a well-defined animal model is
important,” Bateman said.

Study focuses on four types of radiation

In the current study, the mice received a single 2 Gray (Gy) dose,
which is comparable to the single dose of 1-2 Gy that human cancer
patients receive. However, cancer patients receive a series of doses
over the course of therapy, totaling 10-70 Gy. (The amount of
radiation in a Gy varies, because it is calculated based on the
recipient’s weight.)

The mice were divided into five groups. The control group received no
radiation. Each of the remaining four groups received a different type
of radiation: gamma, proton, ion or carbon. Those exposed to the
carbon radiation suffered 39% spongy bone loss; proton, 35%; ion, 34%;
and gamma, 29%. The loss of spongy connections in the four groups
ranged from 46-64%, he said.

Cancer patients typically receive either gamma or, less commonly,
proton radiation. Astronauts on a Mars mission are expected to receive
extended periods of low-dose radiation of multiple types, including
protons and heavy ions, Bateman said.

Source: American Physiological Society