External Beam Radiation Therapy

In external beam radiation therapy, radiation is produced by a machine called a linear accelerator. Short bursts of x-rays are fired from the machine at your cancer. The x-rays come out in a square-shaped manner, and the radiation oncologist designs special blocks to shape the radiation beam so that it treats the cancer and as little normal tissue as possible.

You may be treated with conventional external beam treatment, or your doctor may recommend one of several alternatives. These other methods are often designed to deliver high doses of radiation to the tumor site while still limiting the exposure of surrounding normal tissues.

  • IMRT (Intensity modulated radiotherapy) uses multiple thin beams to focus the highest does of radiation in the area of the tumor.
  • High dose brachytherapy uses catheters and tubes to deliver an extra dose of radiation to the tumor site and may occasionally be used to boost the radiation delivered to the site of a rectal tumor.

]]>Radiation therapy]]> is most often used to treat rectal cancer, metastatic colon or rectal cancer. It may be given in combination with chemotherapy and surgery for colon cancer. It is most often delivered externally with or without the addition of newer techniques, such as intensity modulation (IMRT). It may also be used to deliver an intraoperative dose (IORT) to a cancer. Your doctor will be able to discuss which, if any, of these treatment types is beneficial for you.

Radiation of a Tumor

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Like ]]>chemotherapy]]>, the side effects from radiation result from injury to the normal tissues. There are many new ways that the radiation oncologist can customize your treatment. The goal is to try and kill as much cancer while sparing as much normal tissue as possible. The radiation oncologist will determine how many treatments you will receive. Sometimes treatments are once a day and sometimes twice per day. Each treatment generally only takes a few minutes. The total treatment time can range from 5-8 weeks depending on the total dose required. The most common side effects of radiation for colorectal cancer are gastrointestinal symptoms, including diarrhea, cramping, and irritation of the surface of the bowel (colitis or proctitis). Long-term effects may include adhesions (scarring) between loops of bowel. This can cause blockages of the bowel.

Radiation therapy can be given to treat cancer at its initial site or once it has spread. In some cases, once cancer has spread, radiation is no longer curative. However, the treatments can help resolve problems that the cancer may be causing, including pain and weakness.

Many people believe that once you have received a certain dose of radiation you can no longer get any more treatment. It is true that each tissue in the body can only safely tolerate a certain dose of radiation. However, the therapy is very focused. It is possible that you can get additional treatments to an already treated area or certainly to an area not yet treated. Ask your radiation oncologist about what dose you can safely receive.