Radiation Therapy for Ewing Tumors

Radiation therapy focuses high-energy beams at the tumor from a machine outside the body to kill the cancer cells.

Ewing tumors (Ewing sarcomas) are very sensitive to radiation, so radiation therapy can sometimes be helpful in treating them. It may be used withsurgery, or it may be used instead of surgery, especially if it would be hard to remove the entire tumor. In either case, chemotherapy is usually given before, during, and afterward.

How radiation therapy is done

This type of treatment is given by a doctor called a radiation oncologist. Before treatments start, the radiation team takes careful measurements with imaging tests such as MRI scans to determine the correct angles for aiming the beams and the right dose of radiation. This planning session is called simulation. Patients may also be fitted with a plastic mold resembling a body cast to keep them in the same position each time so that the radiation can be aimed more accurately.

Most often, radiation treatments are given 5 days a week for several weeks. Each treatment is much like getting an x-ray, but the dose of radiation is much higher. The treatment is not painful. For each session, the patient lies on a special table while a machine delivers the radiation from precise angles.

Each treatment lasts only a few minutes, but the setup time – getting the patient into place for treatment – usually takes longer. Some younger children may be given medicine before each treatment to make them sleep so they won’t move during treatment.

Types of radiation therapy

Modern radiation therapy techniques let doctors focus the radiation more precisely than in the past. These techniques include:

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 that can be especially useful for tumors with complex shapes or tumors near important structures, such as the spine. Along with shaping the beams and aiming them at the tumor from several angles, the intensity (strength) of the beams is adjusted to limit the dose reaching the most sensitive normal tissues. This lets the doctor deliver a higher dose to the tumor. Many major hospitals and cancer centers now use IMRT, especially for tumors in hard-to-treat areas such as the spine or pelvis (hip bones).

Conformal proton beam radiation therapy: Proton beam therapy is another type of 3D therapy. But instead of using x-rays, it focuses proton beams on the tumor. Unlike x-rays, which release energy both before and after they hit their target, protons cause little damage to tissues they pass through and then release their energy after traveling a certain distance. Doctors can use this property to deliver more radiation to the tumor and do less damage to nearby normal tissues.

This approach may be helpful for hard-to-treat tumors, such as those on the spine, skull, or pelvic bones. However, the machines needed to make protons are expensive, and there are not many of them in the United States at this time.

Possible side effects of radiation therapy

Because of the possible side effects of radiation therapy (especially in growing children), surgery is often preferred if it is possible. But improvements in the way radiation therapy is given now allow children with Ewing tumors to be treated with lower doses than were used in the past, helping to reduce some of the side effects.

The side effects of radiation therapy depend mainly on the dose of radiation and where it is aimed. Some effects may last only a short time, while others might last longer.

Short-term side effects

Radiation might cause some short-term side effects, which usually go away within a week or two after treatment. For example:

• Radiation can affect the skin in areas that are in the path of the radiation. Effects can range from mild sunburn-like changes and hair loss to more severe skin reactions.
• Radiation might lower blood cell counts. This can be worse if radiation is being given at the same time as chemo, which can also lower blood cell counts.
• Radiation to the head and mouth area might cause mouth sores or dry mouth.
• Radiation to the abdomen or pelvis might cause nausea, diarrhea, or urinary problems.

Late and long-term side effects

Some side effects might last longer, or they might not show up until some time after treatment is finished. These types of side effects can often be more serious, especially in growing children, so doctors try to limit them as much as possible.

A serious effect of radiation therapy in children is slowed bone growth, especially in younger children. For example, radiation to the bones in one leg may result in it being much shorter than the other. Radiation of facial bones may cause uneven growth, which might affect how a child looks. But if a child is fully or almost fully grown, this is less likely to be an issue.

Depending on where the radiation is aimed, it can also damage other organs:

• Radiation to the chest wall or lungs can affect lung and heart function.
• Radiation to the pelvis can damage the bladder or intestines, which can lead to problems with urination, digestion, or bowel movements. It can also damage reproductive organs, which could affect fertility later in life, so doctors do their best to protect these organs by shielding them from the radiation or moving them out of the path of radiation whenever possible.
• Side effects of radiation therapy to the spinal cord or skull may include nerve damage, headaches, and trouble thinking, which usually become most serious a year or two after treatment. Fortunately, Ewing tumors rarely spread to the brain, but they can sometimes extend into the brain from nearby bones of the skull.

Another major concern with radiation therapy is that it might cause a new cancer to form in the part of the body that was treated with the radiation. This is most often a different type of bone cancer called an osteosarcoma. This small risk should not keep children who need radiation from getting it. Still, it’s important to continue follow-up visits with your child’s doctor so that if problems come up they can be found and treated as early as possible.