Radiation Therapy for Eye Cancer

Radiation therapy uses high-energy x-rays to kill cancer cells. It is a common treatment for eye melanoma. Radiation therapy can often save some vision in the eye. Sometimes vision might be lost if the radiation damages other parts of the eye. An advantage over surgery is that the eye structure is preserved, which can result in a better appearance after treatment.

Different types of radiation therapy can be used to treat eye cancers.

Brachytherapy (plaque therapy)

This form of radiation therapy might also be called ocular brachytherapy or episcleral plaque therapy. This has become the most common radiation treatment for most eye melanomas. Studies have shown that in many cases it is as effective as surgery to remove the eye (enucleation).

In this approach, a small carrier containing radioactive “seeds” (known as a plaque) is placed on the outside of the eyeball over where the tumor is. The plaque is typically shaped like a very small bottle cap and has gold or lead on the outside 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. This can sometimes be done with local anesthetic (numbing medicine) and sedation, although sometimes general anesthesia might be needed (where you are in a deep sleep). The plaque is usually left in place for at least a few days, although the exact amount of time depends on the size of the tumor and the strength of the radiation source. You will probably stay in the hospital during this time. Another surgery is then done to remove the plaque. You will probably be able to go home the same day.

The full effect of the radiation on the tumor is not usually seen for 3 to 6 months.

This treatment cures about 9 out of 10 small to medium size tumors and can preserve vision in some people, depending on what part of the eye the melanoma is in. The outlook for vision is not as good if the tumor is very close to the optic nerve, which carries visual images from the eye to the brain.

External beam radiation therapy

In this approach, radiation from a source outside the body is focused on the cancer. For eye melanomas, the use of this type of radiation therapy is generally limited to newer methods that focus narrow beams of radiation on the tumor.

Proton beam radiation therapy: Instead of using x-rays as in standard radiation therapy, this approach aims proton beams toward the cancer. Unlike x-rays, which release energy both before and after they hit their target, protons cause little damage to tissues they pass through and release their energy only after traveling a certain distance. This means that proton beam radiation may be able to deliver more radiation to the tumor but do less damage to nearby normal tissues. This type of radiation treatment is used more often for larger tumors and for tumors that are closer to the optic nerve.

Getting treatment is much like getting an x-ray, but the dose of radiation is much higher. In most cases, the total dose of radiation is divided into daily fractions (usually given Monday thru Friday) over several weeks. The treatment is typically not painful.

The specialized machines needed to make protons are only found in certain centers in the United States at this time.

Stereotactic radiosurgery: Despite the name, there is no actual surgery involved in this treatment. The term "surgery" is used to describe the accurate nature of the radiation beams. This type of treatment delivers a large, precise radiation dose to the tumor area in a single session. It is not used as often as brachytherapy or proton beam therapy as the initial treatment for eye melanomas. Different machines can be used to deliver radiation in one of two ways:

• A Gamma Knife stays in one place and focuses radiation beams from hundreds of different angles at the tumor all at once for a short period of time in one treatment session.
• Several machines, such as CyberKnife® or Clinac® use a computer to control a radiation machine that moves in a circular motion (180 degrees) over the tumor to deliver individual radiation beams at separate times from many different angles. These treatments are done over multiple days.

Possible side effects of radiation therapy

The main concern with radiation therapy is damage to parts of the eye, leading to problems such as blurry vision, dry eye, cataracts, retinal detachment, glaucoma (increased pressure inside the eye), loss of eye lashes, problems with tear ducts, or bleeding into the eye. Some of these treatments can result in partial or complete loss of vision or other problems, which might not happen right away and may worsen with time. The risk depends on the size and location of the tumor.

Because the radiation is focused only on the affected eye, it is not likely to affect vision in the other eye or to cause other side effects sometimes linked with radiation therapy, such as hair loss or nausea.