This article includes discussion of radiation: CNS complications; late radiation effects; radiation side-effects; and radiation toxicity. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.
Several early and late radiation-induced complications of the nervous system have been described. They may include radiation necrosis, cerebrovascular disease, cognitive deficits, endocrinopathies, encephalopathy, myelopathy, plexopathy radiculopathy, neuropathy, and secondary malignancies. This article discusses in detail the various radiation complications and therapeutic options. The author has added 2 new references about radiation-induced myelopathy following radiosurgery and usefulness of SPECT in differentiating recurrent tumor from radiation necrosis.
Historical note and terminology
Most cancer therapies are nonspecifically cytotoxic. This is especially true of radiation therapy. As a result, when radiation therapy is used to treat primary or metastatic nervous system cancers, or nonnervous system malignancies located close to neural structures, injury to the normal nervous system can occur and is often dose-limiting. The most dramatic example of this type of injury, brain radiation necrosis, was first recognized in 1930, soon after radiation was first used therapeutically for brain tumors (Fisher and Holfelder 1930). Since that time, a spectrum of injuries throughout the central and peripheral nervous system has been identified, and some of the details of specific syndromes have been elucidated. Despite this heightened awareness, the neurologic complications of radiation therapy continue to occur because individual tolerances to radiation are variable, safe radiation thresholds are not precisely known (and may be altered by concurrent chemotherapy or preexisting disease), and intentional "overdoses" may be given with curative or long-term palliative intent. In fact, the incidence of radiation-related nervous system injury appears to be increasing as conventional radiation therapy techniques are being applied more aggressively, new approaches (such as brachytherapy and radiosurgery) are becoming commonplace, and patients are surviving longer.
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