Radiation Therapy Principles

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Goals of radiation therapy

Most types of radiation are considered local treatments because the radiation is aimed at a specific area of the body (where there’s a tumor). Only cells in that area are affected. Most forms of radiation therapy can’t reach all parts of the body, which means they’re not helpful in treating cancer that has spread to many distant areas.

Radiation is used to treat cancer in several ways.

To cure or shrink early stage cancer

Some cancers are very sensitive to radiation. Radiation may be used by itself in these cases to make the cancer shrink or disappear completely. Sometimes, a few cycles of chemotherapy are given first. For other cancers, radiation may be used before surgery (as pre-operative or neoadjuvant therapy) to shrink the tumor, or after surgery to help prevent the cancer from coming back (this is called adjuvant therapy).

For certain cancers that can be cured either by radiation or by surgery, radiation may be preferred because it can sometimes preserve the organ’s function (such as that of the larynx or the anus).

In treating some types of cancer, radiation may also be used along with chemotherapy (chemo). This is because certain chemo drugs act as radiosensitizers; they make the cancer cells more sensitive to radiation. These drugs make the radiation work better. The drawback of giving chemo and radiation together is that side effects tend to be worse.

When radiation is used along with other forms of therapy, the treatment is planned by the surgeon, medical oncologist, and radiation oncologist, as well as the patient.

To stop cancer from recurring (coming back) somewhere else

If a type of cancer is known to spread to a certain area, doctors often assume that a few cancer cells might already have spread there, even when imaging scans (such as CT or MRI) show no tumors. That area may be treated to keep these cells from growing into tumors. For example, people with some types of lung cancer may get preventive (or prophylactic) radiation to the head because this type of cancer often spreads to the brain. Sometimes, radiation to prevent future cancer can be given at the same time that radiation is given to treat existing cancer, especially if the prevention area is close to the tumor itself.

To treat symptoms caused by advanced cancer

Sometimes cancer spreads too far to be cured. But even some of these tumors can still be treated to make them smaller so that the person can feel better. Radiation might help relieve symptoms such as pain, trouble swallowing or breathing, or bowel blockages that can be caused by advanced cancer. This is often called palliative radiation.


Last Medical Review: 10/27/2014
Last Revised: 10/27/2014