Thirty or forty years ago, the ability to diagnose and treat an individual with a brain tumor was limited by crude surgical and radiological tools. Modern neurosurgical tools and techniques and advanced imaging modalities such as CT and MRI now allow brain tumors to be identified much earlier in the course of the disease. Even when a cure is not possible, an earlier diagnosis can result in an improved outcome for the patient through more appropriate utilization of radiation therapy.
Radiation therapy uses high energy light beams (X-rays or gamma rays) or charged particles (electron beams or proton beams) to damage critical biological molecules in tumor cells. If enough damage is done to the chromosomes of a cell, it will spontaneously die or it will die the next time it tries to divide into two cells. Radiation therapy is usually done on an outpatient basis with treatment occurring each workday for a period of several weeks. If the patient has had surgery for the tumor, radiation therapy typically begins a week or two after surgery.
Radiation therapy is an effective cancer therapy. In surgery, a surgeon may be constrained in resecting the cancer by the presence of critical structures that cannot be removed. The side effects of chemotherapy on normal tissues far away from the brain may limit the ability of a medical oncologist to deliver appropriately intensive treatment to a brain tumor. In radiation therapy, a non-invasive treatment can be given repetitively over several weeks to months and can be aimed specifically at the area where treatment is needed, minimizing side effects for uninvolved normal tissues.
This repetitive treatment is called fractionation because a small fraction of the total dose is given in each treatment. The skills of the radiation oncologist, physicist and dosimetrist allow complex plans to be devised to minimize side effects for normal tissues. Radiotherapy can only be performed with linear accelerator technology.
Conventionally administered external beam radiation therapy gives a uniform dose of radiation to the entire region affected by the tumor. There is only a small variation of the dose delivered to various parts of the tumor. Radiation therapy may not be as effective as stereotactic radiosurgery, which can give higher doses of radiation to the tumor itself.
Treatment of brain tumors with external beam radiation therapy has been an area of intense research activity over the past several decades. Through clinical research, conducted on patients, much has been learned about how to appropriately use radiation therapy for various types of brain tumors. External beam radiation therapy is a valuable component of therapy for nearly all brain tumors; treatment can be delivered to any part, or all, of the central nervous system. The ability to assure uniform doses of radiation to the areas being treated is one of the major strengths of modern external beam radiation therapy.
There are some side effects that may be seen with radiation therapy for a brain tumor. Specific side effects may also vary with the part of the brain being treated. Radiation therapy for a brain tumor is usually associated with hair loss in the area of the scalp that the X-ray beams are going through; this may be temporary or permanent. It may cause some reddening and scaling of the scalp as well.
Fatigue is commonly seen and there may be loss of appetite or a change in one’s sense of taste. Occasionally, there is nausea and rarely, vomiting; medications usually alleviate these symptoms.
If the inner ear is irradiated while the tumor is being treated, there may be fluid build-up behind the eardrum, which is usually treated with decongestants. Following radiation therapy, there may be persistent fatigue that can sometimes last for several months. Steroids (such as dexamethasone) may lessen some of these symptoms, but the minimum effective dose should be used because of possible systemic side effects.
The most noticeable long-term side effect is a gradual decline in some higher brain functions, which will occur over a few years. Many patients notice this as a memory problem. It would seem reasonable that the area of the brain irradiated and the dose of radiation given would be important factors that might influence this side effect, but this has never been conclusively proven. It is not certain whether this gradual decline in higher brain functions stabilizes after several years, but many patients believe it does.
Very occasionally, radiation therapy given in doses that are safe for the vast majority of patients can cause damage to normal brain tissue, resulting in its destruction. For more information on side effects and radiation injury Click Here.