Orbital radiation therapy is a form of treatment that focuses on using external radiation to destroy white blood cells. The word “orbital” refers to the anatomic term that describes the space enclosed by the borders of the eye socket. The white blood cells that infiltrate the tissues surrounding the eyeballs in the setting of thyroid eye disease are exquisitely sensitive to the effects of the energy delivered by external beams of radiation. Over time, as repeated doses of this energy are directed towards this space, infiltrating white blood cells are gradually destroyed. This may help to reduce the inflammation that contributes to the development of complications. Orbital radiation therapy is usually administered in ten fractionated doses delivered over the course of two weeks.
Responses to treatment with orbital radiation therapy may be marked by decreased inflammation, decreased proptosis, and gradual improvement in the function of compressed optic nerves and trapped extraocular muscles. Side effects may include temporary loss of hair at the temples, the development of cataracts, and damage to the retinas that may impair vision. Orbital radiation therapy may be used in combination with immunosuppressive therapy to treat thyroid eye disease. It may also be used as primary therapy to treat patients who are unable to tolerate side effects associated with the administration of prednisone or cyclosporine A.