Episcleral Eye Plaque Brachytherapy
Prior to the medical milestone of episcleral eye plaque therapy, the only form of treatment for ophthalmic tumors such as choroidal melanoma was enucleation (the removal of the eye). Episcleral eye plaque therapy is intended as an eye-conserving procedure in which a small metallic “plaque” containing sealed radioactive sources is temporarily placed on the eye adjacent to the tumor.
Eye Plaque Procedure Basics
First, the patient’s opthalmic tumor is measured using ultrasound. This is followed by a CT scan, which will indicate the exact size and shape of the patient’s eye. Photographic fundus imaging is also incorporated to create a highly accurate 3-D computer model showing the precise location of the tumor. This information allows the treatment team of radiation oncologists, ophthalmologists, and physicists to determine the proper dose rate, dose prescription, and the selection of the appropriate plaque and seeds, all of which will facilitate the delivery of a highly conformal dose of radiation to the tumor.
While the patent is under general anesthesia, a device called a “plaque” is attached to the eye. The plaque is about the size of an adult’s thumbnail and contains grooves which hold the radioactive seeds. Each seed is approximately a quarter of an inch long and is about the same diameter as the lead in a number 2 pencil.
The seed-loaded plaque is sewn to the eyeball under the top layer of the conjunctiva (the loose connective tissue that covers the white of the eye.) When the plaque is in place it is not visible from the outside, does not interfere with the patient’s vision, and seldom causes any discomfort.
The plaque is removed about a week after the initial surgery, and the size of the tumor is measured and monitored periodically over time, during subsequent patient visits.