Experimental study shows one therapeutic radiation dose decreases trabecular bone

The research findings offer insight into radiation-induced osteoporosis.

A single dose of radiation at a therapeutic level caused almost a 40% loss in trabecular bone in mice, an experimental study found.

“We were really surprised at the extent of bone loss,” Ted A. Bateman, PhD, director of Clemson University’s Osteoporosis Biomechanics Laboratory, said in a press release announcing the results. “We’re seeing bone loss at much lower doses of radiation than we expected.

“It’s interesting that the trabecular bone, not the cortical bone, suffered the damage,” he added.

Bateman conducted the study with colleagues at the center to evaluate the effects of radiation on bone loss. The researchers used female C57BL/6 mice, which were divided into a control group and 4 study groups, each exposed to 2 Gy of a different radiation type — gamma, proton, carbon or iron radiation, according to the study.

After 110 days post-irradiation, the researchers euthanized the mice and analyzed changes to the tibial and femoral diaphyses using microcomputed tomography. They found that all 4 types of radiation caused losses in trabecular architecture.

For carbon radiation, trabecular architecture decreased 39%, while it decreased 35% from proton radiation, 34% from iron radiation and 29% from gamma radiation, according to the study.

Irradiation also affected trabecular connectivity in the 4 radiation groups, ranging from 46% to 64% losses, according to the release.

The study authors noted that there was no previous animal model for radiation-induced osteoporosis.

Clinical studies of cancer patients have been limited because of the complicating factors of both the illness itself and the accompanying chemotherapy. Although the current study results cannot be directly applied to humans, the mouse model does allow research into the physiological effects of radiation exposure.

Bateman noted that a recent clinical study of 6,000 cancer patients, published in the Journal of the American Medical Association, found postmenopausal women treated with pelvic radiation for cervical and colorectal cancer had a 60% increased fracture risk. Radiation following anal cancer increased fracture risk by 200%.

The researchers used the 2-Gy radiation dose because it is similar to the gamma or proton radiation doses used to treat human cancer patients, although such patients typically receive a series of doses over the course of therapy, totaling 10 Gy to 70 Gy, according to the release.

“These data have clear implications for clinical radiotherapy, in that bone loss in an animal model has been demonstrated at low doses,” the authors said in the study.

For more information:
Hamilton SA, Travis ND, Willey JS, et al. A murine model for bone loss from therapeutic and space-relevant sources of radiation. J Appl Physiol. Published online ahead of print. June 8, 2006. Available at http://jap.physiology.org/cgi/content/abstract/01078.2005v2.