Retina Consultants of Southern California works in conjunction with the radiation oncology department at Loma Linda University Medical Center to treat choroidal melanomas with proton beam radiation.
Choroidal melanomas are malignant tumors that arise from pigmented cells in the choroid, which is the vascular layer of the eye directly behind the retina. These tumors usually start as a pigmented spot that is detected on photographs of the retina or on examination of the retina through a dilated pupil. These pigmented areas must be distinguished from moles or freckles, which occur naturally in many normal eyes, and from other types of tumors and lesions which are not always cancerous.
The diagnosis of a choroidal melanoma is most often done by way of indirect tests such as photography, angiography and ultrasound. Some centers routinely do tumor biopsies, but this is controversial since the procedure is technically difficult, with a significant rate of complications which can result in irreversible vision loss.
Biopsies can be done for two reasons. One is to establish the diagnosis. However, biopsies are not always conclusive, and many studies have shown that, even without a biopsy, the incidence of falsely diagnosing a tumor with the previously mentions indirect imaging studies is very low.
The other reason for a biopsy is to perform a genetic profile on the tumor. This can tell us whether the tumor has a high or low risk of spreading by metastasis. This might be very helpful if we had an effective treatment for treating metastatic tumors, but currently we don’t. Giving this information to patients may decrease their anxiety if the results show a low risk of metastasis, but it could be psychologically harmful to tell a patient that they have a tumor with a high risk of metastasis but there is no additional treatment we can offer. For these reasons we currently do not perform biopsies on choroidal melanomas.
How is Treatment Performed?
Proton beam radiation treatment is a 2 step process.The first step is to perform an operative procedure in which tantalum rings are sutured to the sclera, on the outside of the eye, demarcating the edges of the tumor. The purpose of this is to make the margins of the tumor visible with X Ray for calculating the parameters for the proton beam treatment. Tantalum is a nonmagnetic metal, and the rings are approximately the size of the flat end of a pin. This procedure is performed in the operating room under local anesthetic with sedation and takes about an hour. During the procedure the superficial layer of the eye, the conjunctiva, is dissected away from the globe of the eye. The eye socket and the outside wall of the eye are then examined for evidence of extension of the tumor outside of the eye. The eye is then transilluminated by shining a bright light through the pupil, which casts a shadow of the tumor on the sclera. Four tantalum rings are then sewn to the outside wall of the eye, demarcating the edges of the tumor, using permanent sutures.
The conjunctiva is then sutured back into position with dissolvable stitches. After the procedure the tantalum rings can't be seen or felt and the sutures dissolve over a period of approximately 6 weeks. There is only mild discomfort following the surgery which gradually improves over several weeks. The tantalum rings do not have to be removed. They are permanently implanted. They very rarely cause any complications in the future, although on very rare occasions they can become exposed and they can easily be removed if necessary. Since they are nonmagnetic, there is no problem with performing an MRI with the tantalum rings in place.
The second step in the process is the proton beam radiation treatment. After the eye has had a sufficient time to heal, and the patient is comfortable, a facial mask is created by the radiation oncology department in order to help in positioning the patient during treatment. The treatment itself is performed at Loma Linda University Medical Center, as an outpatient, over several consecutive days.
The follow up visits after proton beam radiation treatment are intended to detect any evidence of tumor growth, tumor spread outside of the eye, or complications from the radiation treatment.
The patient is usually monitored by a retina specialist to detect any evidence of tumor growth. This usually requires three or four visits within the first six months, and every six months thereafter. If definite evidence of tumor growth is detected, additional radiation treatment is sometimes possible, but in some cases enucleation, or removal of the eye, is recommended.
A yearly work up by the patient’s primary care physician is recommended to detect any evidence of tumor spread, or metastasis. This usually includes liver function tests, chest X Ray, and an abdominal CT scan.
Complications of Radiation Treatment
We feel that proton beam radiation treatment has an advantage over other conventional forms of radiation, since the proton beam can be focused directly on the tumor, resulting in less collateral damage to adjacent tissues. However, complications can occur with any form of radiation treatment.
1. Short term side effects
Redness and irritation of the eyelids
2. Long term complications
Some of these side effects can be self-limited and resolve overtime without treatment. Others can be successfully treated, but permanent vision loss is always a possibility. It is important to understand that the goal of treatment is to prevent a fatal metastasis of the tumor. Every effort is made to reduce the likelihood of complications, but sometimes these are unavoidable.
Although the overall success rate of proton beam radiation treatment for choroidal melanomas is very good, the likelihood of successfully treating a tumor depends on multiple factors including tumor size, location, and genetic profile. Prior to treatment a full systemic work up is always performed to detect any tumor spread that has occurred outside of the eye. Your doctors will discuss your specific prognosis and whether you are a good candidate for proton beam radiation treatment.