Radiation Therapy Used to Treat Ocular Melanoma While Preserving the Eye

From Mallinckrodt Institute of Radiology Focal Spot, Spring 2003, Volume 34, Number 1 by Vicki Kunkler

Ocular melanoma, or cancer of the eye, is one of the rarest forms of cancer. But choroidal melanoma, a tumor affecting the pigmented portion (choroid) of the eye tissue, is the most common type of eye cancer in adults. Over time, the tumor can enlarge, cause vision loss, and spread to other parts of the body.

Approximately 2,000 cases are diagnosed per year in North America and for more than a century, the standard treatment has been enucleation-or surgical removal of the eye. Now, radiation oncologists and ophthalmologists at Washington University Medical Center are recommending radiation therapy as an effective, conservation treatment for medium-size choroidal melanoma.

"Radiation has been used to treat ocular melanoma for around fifty years," says radiation oncologist Hsiu-san Lin, MD, PhD, "but within the past twenty years, the technique has been refined with the availability of better radioactive sources and the advent of practical treatment planning software." Lin, professor of radiation oncology and associate professor of molecular microbiology, heads the bistate region's only active eye plaque brachytherapy center. The center's treatment team is comprised of a radiation oncologist, an ophthalmologist, a medical physicist, and a brachytherapy technologist.

In eye plaque brachytherapy, small radioactive seeds are embedded in a plaque-a bowl-shaped device made of gold-that is fitted to each patient. This is pictured above. Patients receive either local or general anesthesia during the surgery to implant the plaque, which takes one to two hours. The ophthalmologist makes a small incision in the membrane (conjunctiva) covering the outside of the eye and sutures the plaque onto the surface of the eye over the base of the tumor. The conjunctiva is then sutured back into place over the plaque.

High doses of ionizing radiation from the radioactive iodine (I25) seeds can be directed via the plaque to the tumor, while sparing healthy surrounding tissue. The cells begin to die and, in most cases, the tumor shrinks within two to three months of therapy. Surgery-taking less than an hour- is required to remove the plaque and is usually performed within three to seven days following implantation.

"Most importantly, the eye is preserved, there is no cosmetic disfiguration, some visual function is retained, and no harm is caused to the other eye," says Lin. "Our success rate in eradicating the tumor in the eye is ninety-five percent, and the rate of tumor recurrence is quite low with brachytherapy."

Lin works closely with William Harbour, MD, associate professor of ophthalmology and director of the Ocular Oncology Service at Barnes Retina Institute at Washington University Medical Center. On average, Harbour refers 30 patients annually for eye plaque brachytherapy.

Under Harbour's leadership, Washington University was one of 43 clinical centers in the United States and Canada that participated in the Collaborative Ocular Melanoma Study (COMS). Initiated in 1986, the study was supported by the National Eye Institute and the National Cancer Institute, both affiliated with the National Institutes of Health.

One of the COMS goals was to determine through a randomized, controlled clinical trial whether patients with medium-size choroidal melanomas treated with eye plaque brachytherapy would survive as long as those patients who underwent enucleation. A medium-size tumor was defined as 2.5 millimeters to 10.0 millimeters in apical height and 16.0 millimeters or less in basal diameter.

From the more than 8,700 patients screened, there were 1,317 patients enrolled and clinically observed through mid 2000. Patients consented to be randomly assigned to undergo either enucleation or brachytherapy. The initial COMS findings published in 2001 reported the same survival rates for patients who had radiation therapy as for those who had the diseased eye surgically removed. As a result of this study, most ocular oncology centers are recommending more brachytherapy and less enucleation in appropriate patients.

Another issue to consider is the patient's quality of life. In brachytherapy, there is a chance of vision loss in the irradiated eye, but most patients retain useful vision. In less than five percent of patients, severe radiation complications require that the eye be removed. Patients undergoing brachytherapy have generally responded more positively to quality of life studies than have patients undergoing enucleation.

"Due in large part to the outstanding collaborative relationships that we have with Doctor Lin's group, our Ocular Oncology Service has grown into one of the top ten referral centers nationally for the treatment of eye cancer," says Harbour.