Stereotactic radiosurgery is based on the same principles as other forms of radiation treatment. It does not remove the tumor or lesion, but the radiation beams distort the DNA of the tumor cells. The cells then lose their ability to reproduce and retain fluids. The tumor reduction occurs at the rate of normal growth for the specific tumor cell. In lesions such as AVMs (a tangle of blood vessels in the brain), radiosurgery causes the blood vessels to thicken and close off. The shrinking of a tumor or closing off of a vessel occurs over a period of time. For benign tumors and vessels, this will usually be 18 months to two years. For malignant or metastatic tumors, because these cells are very fast-growing, results may be seen in a few months.
- Swelling: As with all radiation treatments, the tumor cells lose their ability to regulate fluids, and edema or swelling may occur. This does not happen in all treatments. If swelling does occur, and it causes symptoms that are unpleasant, then a mild course of steroid medication may be given to reduce the fluid within the tumor cavity.
- Necrosis: The tumor tissue that remains after the radiation treatment will typically shrink. On rare occasions this necrotic or dead tissue can cause further problems and may require removal. This occurs in a very small percentage of cases.
- Other effects: Other side effects may occur dependent upon the target site and the dose of radiation received. This should be discussed thoroughly with your physician.
Because all forms of radiation treatments work over time, this course of treatment may be inappropriate if symptoms are severe or life-threatening. For example, if relief of acute symptoms is urgent, the first treatment choice may be traditional open surgery or medication to relieve symptoms affecting quality of life. Secondary treatment may then be radiosurgery. In other cases where cells are extremely fast growing (with or without severe symptoms), such as in brain metastases, radiosurgery can quickly control the brain tumors to allow time to treat the primary cancer site. Medication can be given for the side effects (such as edema), and radiation therapy may be used over a period of time to help eliminate stray cancer cells from the brain.
Stereotactic radiosurgery can be used in patients where standard radiation techniques have failed, or in patients where the maximum radiation dose permissible has been administered. There is little literature on radiation-induced new tumors caused by stereotactic radiosurgery. It is expected that the possibility of developing a tumor is 1 in 10,000 cases. This may be attributed to the precision of the treatment and the sparing of healthy nerves and tissues. A patient who has had stereotactic radiosurgery for a tumor or another condition may have open surgery later without problems. In many cases, stereotactic radiosurgery can be performed again if necessary.
There are three basic forms of stereotactic radiosurgery represented by three different technological instruments. Each instrument operates differently, has a different source of radiation and may be more effective under different circumstances.
- Cobalt-60 based (photon)
- Linear accelerator based (linac)
- Particle beam (proton)
Stereotactic radiosurgery may or may not be appropriate for a condition. It may be used as the primary treatment or recommended in addition to other treatments that are needed. The members of the multi-disciplinary radiosurgery treatment team make the determination as to whether or not someone can be treated.