Radiation therapy for Wilms tumor

Radiation therapy uses high-energy rays or particles to kill cancer cells. Radiation therapy is usually part of treatment only for more advanced Wilms tumors (stages III, IV, and V) and for some earlier stage tumors with unfavorable histology.

The type of radiation used for Wilms tumors, known as external beam radiation therapy, focuses radiation from outside the body on the cancer. It is much like getting an x-ray, although the dose of radiation is much higher. The total dose of radiation is divided into daily fractions, usually given over a couple of weeks.

Before treatments start, the radiation team takes careful measurements with imaging tests such as CT or MRI scans to determine the correct angles for aiming the radiation beams and the proper dose of radiation.

For each treatment session, your child lies on a special table while a machine delivers the radiation from a precise angle. Your child may be fitted with a plastic mold resembling a body cast to keep him or her in the same position each time so that the radiation can be aimed more accurately. Each session lasts about 15 to 30 minutes, with most of the time being spent making sure the radiation is aimed correctly. The actual treatment time each day is much shorter. The treatment is not painful, but some younger children may be given medicine to make them drowsy before each treatment to help make sure they stay still.

Some newer radiation techniques allow doctors to focus the radiation more precisely.

Three-dimensional conformal radiation therapy (3D-CRT)

3D-CRT uses the results of imaging tests such as MRI and special computers to precisely map the location of the tumor. Several radiation beams are then shaped and aimed at the tumor from different directions. Each beam alone is fairly weak, which makes it less likely to damage normal body tissues, but the beams converge at the tumor to give a higher dose of radiation there.

Intensity modulated radiation therapy (IMRT)

IMRT is an advanced form of 3D therapy. In addition to shaping the beams and aiming them at the tumor from several angles, the intensity (strength) of the beams can be adjusted to limit the dose reaching the nearby normal tissues. This may allow the doctor to deliver a higher dose to the tumor. Many major hospitals and cancer centers now use IMRT.

Possible side effects of radiation therapy

Radiation is often an important part of treatment, but young children’s bodies are very sensitive to it, so doctors try to use as little radiation as possible to help avoid or limit any problems. Radiation therapy can cause both short-term and long-term side effects. Side effects depend on the dose of radiation and where it is aimed.

Possible short-term effects:

• Effects on skin areas that receive radiation can range from mild sunburn-like changes and hair loss to more severe skin reactions.
• Radiation to the abdomen (belly) can cause nausea or diarrhea.
• Radiation therapy can make a child tired, especially toward the end of treatment.

Possible long-term effects:

• Radiation therapy can slow the growth of normal body tissues (such as bones) that get radiation, especially in younger children. In the past this led to problems such as short bones or a curving of the spine, but this is less likely with the lower doses of radiation used today.
• Radiation that reaches the chest area can affect the heart and lungs. This does not usually cause problems right away, but in some children it may eventually lead to heart or lung problems as they get older.
• Radiation to the abdomen in girls may damage the ovaries. This might lead to abnormal menstrual cycles or problems getting pregnant or having children later on.
• Radiation can damage DNA. As a result, radiation therapy slightly increases the risk of developing a second cancer in the areas that get radiation, usually many years after the radiation is given. This doesn't happen often with Wilms tumor because the amount of radiation used is low.

Parents should continue to have their child watched closely by doctors so that they can treat any problems quickly if they come up. See the section, “What happens after treatment for Wilms tumor?” for more on the possible long-term effects of treatment.

For more information on radiation therapy, see the separate American Cancer Society document, Understanding Radiation Therapy: A Guide for Patients and Families.