Answer to Question #538 Submitted to "Ask the Experts"

Q

What are the different effects of radiation on the different connective tissues and how does it affect them? What are the mechanisms involved? Thank you!

A

There are no observable effects of small doses of radiation (such as those from environmental or diagnostic medical sources) on connective tissue. With larger doses (such as those delivered to part of the bodies of patients undergoing radiation therapy) the effects closely resemble the sequelae of inflammation: fibrosis, commonly called scarring. This is not surprising; tissues respond to any injury by inflammation—unless the injury is sufficient to cause necrosis (death of tissue). In the usual inflammatory response, dying or severely injured cells release chemical mediators which induce capillary leakage of both fluid (edema) and white blood cells (immune response). In connective tissues, radiation directly injures the endothelial lining of capillaries, leading to the same result. After healing, the result of radiation is perivascular fibrosis, which causes an increase in the barrier between the microvasculature and the dependent tissue. This leads to hypoxic injury of dependent tissue cells, resulting in release of chemical mediators of inflammation, setting up a cyclic phenomenon that increases in severity with time. This response appears common to all connective tissues. S. Julian Gibbs, DDS, Ph.D.