Radiation therapy uses high-energy radiation to kill cancer cells. It is a common treatment for intraocular melanoma. Radiation therapy can often preserve some vision, although sometimes this is lost anyway because radiation damages other parts of the eye. Its main advantage is that the eye structure is preserved, which may result in a better appearance for the patient.
Different types of radiation therapy can be used to treat eye cancers.
Brachytherapy (episcleral plaque therapy)
This form of radiation therapy places small pellets (sometimes called seeds) of radioactive material directly into or very close to the cancer. This has become the most commonly used radiation treatment for most eye melanomas. Studies have shown that in many cases it is as effective as surgery (enucleation).
The pellets of radioactive material (usually radioactive iodine, ruthenium, or palladium) are attached to a small carrier (shaped like a very small bottle cap), which is placed on the outside of the eyeball with tiny stitches to keep it in place. The carrier is made of gold or lead to shield nearby tissues from the radiation. The radiation from the pellets travels a very short distance, so most of it will be focused only on the tumor.
An operation is needed to put the plaque (radioactive element and carrier) in place. This surgery usually takes 1 or 2 hours. The plaque is usually kept there for 4 to 7 days, depending on the size of the tumor and the strength of the radiation source. You will probably remain in the hospital during this time. Surgery to remove the plaque usually takes less than an hour, and you will probably be able to go home the same day. The full effect of the radiation on the tumor is not seen for 3 to 6 months.
This therapy cures about 9 out of 10 small tumors and can preserve vision in some patients, depending on what part of the eye the melanoma is in. The outlook for vision is less favorable if the tumor is located very close to the optic nerve, which carries signals 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. This is the type of radiation therapy used to treat eye lymphomas. For melanoma the use of this type of radiation therapy is generally limited to newer methods that focus narrow beams of radioactivity on the tumor. These techniques have not yet been widely used.
Conformal proton beam radiation therapy: Instead of using x-rays as in standard radiation therapy, this approach focuses proton beams on the cancer. Protons are positive parts of atoms. 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. This means that proton beam radiation may be able to deliver more radiation to the tumor and do less damage to nearby normal tissues.
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 not painful.
The machines needed to make protons are expensive, and there are only a handful of them in use in the United States at this time.
Stereotactic radiosurgery: This is a type of radiation treatment that delivers a large, precise radiation dose to the tumor area in a single session. (There is no actual "surgery" involved in this treatment.) The radiation may be delivered in one of two ways.
In one approach, radiation beams are focused at the tumor from hundreds of different angles for a short period of time. The machine used to deliver this type of radiation is known as a Gamma Knife.
A similar approach uses a movable linear accelerator (a machine that creates radiation) that is controlled by a computer. Instead of delivering many beams at once, this machine moves around the head to deliver radiation to the tumor from many different angles. Several machines do stereotactic radiosurgery in this way, with names such as X-Knife, CyberKnife, and Clinac.
Possible side effects of radiation therapy
The main concern with radiation therapy is damage to other parts of the eye, leading to problems such as cataracts, retinal detachment, glaucoma, and bleeding into the eye. These can result in loss of vision or other problems, which may not happen right away. The risk depends on the size and location of the tumor.
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