Radiation Therapy for Retinoblastoma

Radiation therapy is an effective treatment for some children with retinoblastoma. Compared with surgery, it has the advantage of possibly saving vision in the eye.

Radiation uses high-energy x-rays or particles to kill cancer cells. Two types of radiation therapy can be used to treat children with retinoblastoma: brachytherapy and external beam radiation therapy.

Brachytherapy (plaque radiotherapy)

The use of brachytherapy, also known as internal radiation therapy or episcleral plaque radiotherapy, is limited to small tumors.

During brachytherapy, a small amount of radioactive material is placed on the outside of the part of the eyeball where the tumor is, and it stays there for several days. The radioactive material is put in a small carrier (known as a plaque), which is shaped like a very small bottle cap. The plaque is made of gold or lead to shield nearby tissues from the radiation. The radiation travels a very short distance, so most of it will be focused only on the tumor.

The plaque is sewn in place on the eyeball with tiny stitches during a short operation. It is then removed during a second operation several days later. Both operations are done while the child is asleep (under general anesthesia).

Possible side effects of brachytherapy

Brachytherapy is less likely to cause side effects than external radiation. The main concern is damage to the retina or optic nerve, which can affect vision many months later. Recent advances in treatment may make this problem less likely. Brachytherapy has not been linked to an increased risk of developing a second cancer.

External beam radiation therapy (EBRT)

EBRT uses a machine to focus a beam of radiation on the cancer from a radiation source outside the body. This was once a common treatment for retinoblastoma. Because of the side effects it can cause, it is now most often used only for cancers that are not well controlled with other treatments.

How EBRT 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 radiation beams and the proper dose of radiation. This planning session is called simulation. The radiation field, or area where radiation will be given, and the dose will be defined based on these tests.

Radiation is usually given 5 days a week for several weeks. Each treatment is like getting an x-ray, although the dose of radiation is much stronger. For each session, your child will lie on a special table while a machine delivers the radiation from precise angles.

Each session lasts only a few minutes. Most of the time for the treatment is spent making sure the radiation is aimed correctly. It is important that radiation is given to the exact field planned in the simulation. Patients may be fitted with a plastic mold that looks like a cast to hold them in the same spot for each treatment. Younger children may be given medicine before each treatment to make them sleep so they will not move during treatment.

Newer forms of EBRT

Many centers now use newer types of EBRT, which can target the tumor more precisely. This lowers the doses that surrounding normal tissues get, which may help reduce side effects.

Possible side effects of EBRT

Some of the side effects of radiation tend to go away after a short while and are usually not serious. Short-term problems might include:

• Mild sunburn-like changes to more severe skin reactions in the radiation field
• Hair loss (such as eyelashes or eyebrows)

More importantly, radiation can create long-term damage to some nearby tissues. This might lead to longer-term side effects, which might include:

• Cataracts, or clouding of the lens of the eye
• Damage to the retina or optic nerve, reducing vision
• Damage to the lacrimal gland (the structure that makes tears), causing dry eye
• Slowed growth of the bones and other tissues near the eye, which can change the way the area looks over time
• Second cancers due to damaged DNA inside exposed cells

Newer forms of EBRT, such as IMRT and proton beam therapy, target the tumor more precisely and spare more normal tissue. This may make some of these side effects less likely than in the past.