Radiation therapy is one component in the treatment of tumors of the nervous system. It is directed at the general area (such as the whole head) when people have several tumors or a tumor that does not have distinct borders. When the tumor has distinct borders, therapy can be directed specifically at the tumor.
Radiation from these treatments sometimes damages the nervous system, despite the best efforts to prevent damage.
Whether damage occurs and how severe it is depend on several factors:
How much radiation is given over the entire course of treatment (total cumulative dose)
How much radiation is given in each dose
How long the treatments are given
How much of the nervous system is exposed to radiation
How susceptible the person is to radiation damage (susceptibility depends on age, genetic susceptibility, general state of health, and other factors)
Giving radiation therapy over several days to several weeks increases its effectiveness and reduces damage to normal tissue.
Symptoms of radiation damage may be
Acute: Occurring in the first few days
Early-delayed: Occurring in the first few months of treatment
Late-delayed: Occurring several months or years after treatment
Symptoms can remain the same or worsen and can be temporary or permanent.
Acute encephalopathy
Early-delayed radiation damage can cause symptoms similar to those of acute encephalopathy. Symptoms of early-delayed damage may develop in children when whole-brain radiation therapy is used to treat leukemia. These symptoms usually diminish on their own over several days to weeks, sometimes more rapidly if corticosteroids are used.
If radiation is directed at the spine in the neck or upper back, early-delayed radiation myelopathy may develop. This disorder sometimes causes a sensation similar to an electric shock. The sensation begins in the neck or back, usually when the neck is bent forward, and shoots down to the legs (a response called Lhermitte sign). Early-delayed radiation myelopathy usually resolves without treatment.
Late-delayed radiation damage causes symptoms many months or years after radiation therapy. This type of damage can develop in children and adults who receive whole-brain radiation therapy. The most common cause in children is radiation therapy to treat a type of brain tumor called medulloblastoma. For most other tumors, radiation therapy is avoided in children because some organs and tissues including the brain, are more sensitive to radiation than in adults. Thus, damage due to radiation therapy is more likely. Symptoms of late-delayed radiation damage can include progressively worsening dementia, memory loss, difficulty thinking, personality changes, and unsteadiness in walking.
Radiation directed at tumors near the spine may damage the spinal cord itself. When it does, late-delayed myelopathy may develop. Often, the first symptoms of myelopathy are progressive loss of sensation, inability to detect the position of the hands or feet, and weakness. When people bend their neck, they may feel an electrical shock or a tingling sensation shooting down the back, down both legs, down one arm, or down one side of the body (Lhermitte sign).
Late-delayed radiation myelopathy can be permanent and often results in paralysis.
