Radiation Therapy for Rhabdomyosarcoma

Radiation therapy uses high-energy radiation to kill cancer cells. It is often an effective way to kill cancer cells that can’t be removed with surgery. When radiation therapy is used to help treat rhabdomyosarcoma (RMS), it is typically given along with chemotherapy.

When might radiation therapy be used?

Radiation is most often used when some of the main tumor is still left after surgery (clinical group II or III), or if removing the tumor completely would mean loss of an important organ, like the eye or bladder, or would be disfiguring. It is not usually needed for children with embryonal rhabdomyosarcoma (ERMS) that can be removed completely by surgery (clinical group I).

Usually radiation therapy is given to any area of remaining disease after 6 to 12 weeks of chemotherapy. An exception is when a tumor near the meninges (linings of the brain) has grown into the skull bones, into the brain itself, or into the spinal cord. These patients are usually given radiation therapy right away (along with chemotherapy).

If the cancer has spread to another part of the body, radiation might be given to certain areas of known cancer spread to reduce any symptoms it is causing.

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 proper dose of radiation. This planning session is called simulation. Patients may also be fitted with a plastic mold resembling a body cast to hold them in the same position each time so that the radiation can be aimed more accurately.

Radiation is usually given 5 days a week for many weeks. Each treatment is much like getting an x-ray, although the dose of radiation is much stronger. For each session, the patient lies on a special table while a machine delivers the radiation from precise angles. The treatment is not painful.

Each session lasts about 15 to 30 minutes, with most of the time spent making sure the radiation is aimed correctly. The actual treatment time each day is much shorter. 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 help doctors aim the treatment at the tumor more accurately than they could in the past.

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. Radiation beams are then shaped and aimed at the tumor from several directions. Each beam alone is fairly weak, which makes it less likely to damage normal body tissues, but the beams come together at the tumor to give a higher dose of radiation there.

Intensity-modulated radiation therapy (IMRT): IMRT is an advanced form of 3D therapy. 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 doctors deliver a higher dose to the cancer areas. Many major hospitals and cancer centers now use IMRT.

Brachytherapy (internal radiation therapy): Another approach is to insert a radioactive source into or near the tumor for a short time. The radiation travels only a short distance, so the tumor gets most of the radiation. This approach may be especially useful in treating some bladder, vaginal, and head and neck area tumors. Some early studies suggest that this may be a good way to preserve the function of these organs in many children.

Other newer techniques, such as stereotactic radiotherapy and proton beam radiotherapy, are discussed briefly in What’s New in Rhabdomyosarcoma Research?

Possible side effects

The side effects of radiation therapy depend on where the radiation is aimed, the dose of radiation, and the person's age. (Young children are much more likely to be affected by radiation.) Some side effects are likely to last a short time, while others might last longer.

Short-term side effects can include:

• Fatigue
• Increased risk of infections
• Effects on the skin in areas that receive radiation, ranging from hair loss and mild sunburn-like changes to more severe skin reactions
• Nausea, vomiting, and diarrhea (from radiation to the abdomen or pelvis)
• Damage to the bladder, which might cause urinary problems (from radiation to the abdomen or pelvis)
• Mouth sores and loss of appetite (from radiation to the head and neck area)

Long-term side effects can be more serious, especially in growing children, so doctors try to limit them as much as possible.

Small children’s brains are very sensitive to radiation, so doctors try to avoid using radiation to the head whenever possible. If it is needed, it is aimed very carefully to try to limit how much reaches the brain. Side effects of radiation therapy to the brain can include headaches and problems such as memory loss, personality changes, and trouble learning at school. These problems tend to become most serious 1 or 2 years after treatment.

Other long-term problems can include the formation of scar tissue and the slowing of bone growth in areas that get radiation. Depending on the child’s age and what parts of the body get the radiation, this could result in deformities or a failure to grow to full height. Radiation can also raise the risk of cancer many years later. (For more on long-term side effects, see What Happens After Treatment for Rhabdomyosarcoma?)

To limit the risk of serious long-term effects from radiation, doctors use the lowest dose of radiation therapy that is still effective.