Radiation therapy uses high-energy rays or particles to destroy cancer cells. Radiation may be used for eye cancer:
The amount of radiation given during treatment, and when and how it is given, will be different for each person. The type of radiation therapy used will depend on the type and stage of eye cancer being treated.
Radiation can often preserve some vision. However, radiation may sometimes damage other parts of the eye and cause vision loss. The structure of the eye is preserved with radiation therapy, so the person’s appearance is not affected as much with this treatment.
Brachytherapy is internal radiation therapy. A radioactive material (radioactive isotope) is placed onto, or very close to, the tumour. Small pellets (or seeds) of radioactive material enclosed in a concave container (or carrier) is placed directly on the eye. This is called plaque therapy or plaque radiation therapy. The radiation kills the cancer cells over time.
Plaque therapy is the most common type of radiation therapy used to treat eye melanomas. For medium-sized eye melanomas, it is as effective as surgery. Radioactive materials can also be placed in the area where the tumour was removed after surgery.
Surgery is done to place the radioactive plaque (or disc). The radioactive plaque is placed over the eye tumour and sewn into the sclera to keep it in place. This usually takes 1–2 hours. The plaque is left in place for about 4–7 days, depending on the type and dose of the radiation that is given. Some types of radioactive materials used for plaque therapy include iodine-125, ruthenium and palladium. Other radioactive materials may be used as well.
The person usually stays in the hospital while the plaques are in place because special radiation precautions are needed. When the desired dose of radiation therapy has been delivered, the plaque is surgically removed.
There is less chance of damaging surrounding tissues with plaque therapy because the radiation is placed close to the tumour. However, plaque radiation therapy can cause some damage to the blood vessels in the eye. Vision can be preserved in some people, depending on the location of the tumour. The container or carrier for the pellets is usually made of gold and helps shield nearby tissues from radiation. Most of the radiation from the pellets is directed to the tumour.
Brachytherapy can be used to treat small to medium-sized eye melanomas. It may take 3–6 months for radiation to stop the growth of the tumour.
Some types of eye cancer are also treated with external beam radiation therapy. A machine directs radiation to the tumour and some of the surrounding tissue.
External beam radiation therapy to the eye is used most often to treat ocular lymphoma. It can also be used for eye melanomas. There are a few different types of external beam radiation therapy that may be used to treat eye melanoma, such as stereotactic radiation therapy and proton beam (charged particle) radiation therapy.
Before having external beam radiation therapy, the person with eye cancer may need to have a small operation to put in metal clips (tags) at the back of the eye. These are used to help plan and deliver the treatment. The clips are put in under general anesthetic and stay in place after treatment, but do not affect vision.
For some types of eye-related tumours, such as eyelid tumours, the lens of the eye is shielded to protect it during radiation therapy.
Proton beam radiation therapy is a form of external radiation that uses high-energy (charged) proton particles instead of x-ray beams. Proton beam radiation therapy is also called charged particle radiation therapy. Protons deliver a higher dose of radiation, but cause less damage to nearby tissues than conventional external beam radiation therapy because they can be aimed more precisely at the target tissues in the eye.
Proton beam radiation therapy is occasionally used for melanoma of the eye, except for very large melanomas. It is not used very often to treat intraocular melanoma.
The treatment is usually given once a day over several weeks. However, because this type of radiation therapy requires special equipment, it is not widely available in Canada.
Stereotactic radiation therapy is another type of external beam radiation therapy that may be used to treat eye melanomas in some situations. Stereotactic radiation therapy allows radiation beams to be given to a specific area. It may be used for tumours at the back of the eye near the optic nerve, if plaque radiation therapy cannot be used.
Stereotactic radiosurgery (SRS) delivers a single high dose of radiation to the tumour (called a single fraction). Stereotactic radiosurgery doesn’t involve surgery at all – an incision is not made and tissue is not surgically removed.
This treatment is usually given over 5 days. However, this type of radiation therapy requires specialized equipment and training, so it may not be available at all cancer treatment centres in Canada.