The same traits that make proton therapy a good option for patients with cancer in other areas - the prostate and the brain, for instance - make proton therapy ideal for treating cancer of the eye.

Because the eyes are surrounded by such important structures and vulnerable tissues, it's important to treat eye cancer with radiation that can be carefully controlled. Because proton therapy is more precise than conventional radiotherapy, oncologists can deliver powerful doses of proton therapy to the tumor site without causing unnecessary damage to surrounding tissue in the eye and head.

Types of Eye Cancer Treated with Proton Therapy

Eye Melanoma

Eye melanoma starts from pigment cells called melanocytes, which are found throughout the eye. The most common eye melanoma involves the part of the eye called the uvea. The uvea includes the iris, which forms the colored part of the eye; the ciliary body, which helps change the shape of the lens inside the eye so that it can focus; and the choroid, which is the posterior part of the eye deep to the retina and the most common site of involvement of uveal melanoma. Though it is uncommon, uveal melanoma is the most common primary eye tumor in adults; approximately 2000-2500 people are diagnosed with the disease each year in the United States. Factors associated with the disease's development include light skin color, environmental exposure and genetic predisposition. Other eye melanomas arise from the conjunctiva, the lining of the anterior surface of the eye and inner surface of the eyelids.

If the melanoma begins in the iris or conjunctiva, it may appear as a dark spot on the eye. However, if it begins in the ciliary body or choroid, symptoms may appear as vision problems or cancers are detected during a routine examination. The diagnosis of uveal melanoma is usually established through clinical findings and biopsy is typically not required, although it may be done to confirm malignancy or for gene expression profiling to determine how likely the cancer will spread to other parts of the body.

Historically, the standard treatment for intraocular melanoma was surgical removal of the eye, or enucleation.  This remains the standard for very large tumors or when preferred by patients. Because of this procedure's effect on a patient's appearance and visual function, eye-sparing alternative therapy, mainly with radiotherapy, is preferred by most doctors and patients when feasible. Randomized trials have established the safety and efficacy for the eye-sparing approach, which does not compromise survival, with clear physical and psychological benefits over enucleation. Eye-sparing treatments include proton therapy, radiation with radioactive plaques, laser photocoagulation, transpupillary thermotherapy and cryotherapy. Of these, proton therapy appears to offer the best tumor control with eye preservation and a low risk of damage to healthy tissue around the eye. The efficacy of proton therapy for uveal tract melanomas has been assessed in multiple studies resulting in a very high chance of tumor control. With proton therapy, however, most patients are able to retain the affected eye.

Eye metastasis

Eye metastasis is a cancer of the eye that occurs when a cancer spreads to the eye from another primary site.  Although the eye is rarely involved with metastasis, this most commonly happens with primary cancers of the breast, lung, and thyroid gland, and the choroid is the most commonly involved metastasis site in the eye; in these situations, the goal of treatment is to improve the patient's quality of life by preserving the eye and vision when feasible. As with primary eye melanoma, proton beam therapy can be used to apply more precise radiotherapy to the eye metastasis while sparing the uninvolved eye and other sensitive tissue around the treatment site.  Recent studies have demonstrated the effectiveness of proton therapy in the management of eye metastasis.

Retinoblastoma

Retinoblastoma is an uncommon pediatric cancer of the eye. It begins in the retina, a nervous tissue that lines the back of the eye, senses light and sends images to the brain. Retinoblastoma accounts for about 3% of cancers in children younger than 15 years - about 4 cases per million. It most often occurs before the age of two, with 95% of retinoblastoma diagnosed before the age of five. The tumor may affect one eye (about 75% of cases), or both eyes (25% of cases). More than 90% of retinoblastomas that do not spread beyond the eye will be cured. Retinoblastoma is sometimes caused by an inherited gene mutation; when it occurs in both eyes, it is always the result of a gene mutation.

Treatment of retinoblastoma requires a multidisciplinary approach and should emphasize curing the cancer as well as retaining vision. If the tumor is especially large, or if there is little expectation of retaining normal vision, surgery may be considered. Other options include cryotherapy, photocoagulation, chemotherapy and radiation therapy. External beam radiation therapy with protons has been used in select cases to control tumors. Proton therapy avoids unnecessary irradiation of normal ocular tissues.

Choroidal hemangiomas

Choroidal hemangiomas are benign vascular tumors that often result in vision loss from associated retinal detachments. Treatment of choroidal hemangiomas is meant to reduce fluid collection under the retina and decrease the size of the tumor. Standard treatment involves photodynamic therapy, photocoagulation, and transpupillary thermotherapy. In recent years, radioactive plaque treatment and proton beam radiation treatments have been used to successfully treat tumors that recur or don’t respond to standard therapies. Proton beam therapy shares the precise tumor targeting ability of radioactive plaques but provides a more even dose to the entire tumor.