Answer
Plaque brachytherapy (see the image below) is a widely accepted alternative to enucleation for medium-sized posterior uveal melanomas (< 10 mm in height and < 15 mm in diameter).
Intraoperative photograph showing placement of a radioactive plaque for posterior choroidal melanoma.
Plaques containing various radioactive isotopes (eg, iridium, cobalt, and ruthenium) have been used. The most common material used in modern plaques is iodine-125, because of its lower energy emission (lack of alpha and beta rays), its good tissue penetration, and its commercial availability.
Radiation from this source causes tumor destruction through damage of DNA in cancerous cells and tumor vessels, with consequent tumor necrosis and regression. However, it is not devoid of complications. Detorakis et al found that after iodine-125 brachytherapy for choroidal melanoma, iris and anterior chamber angle neovascularization developed in 23% of eyes. [14]
A computerized calculation is used to determine the dose and the duration of plaque application for a radiation delivery of approximately 400 Gy to the base and 80-100 Gy to the apex of the tumor, at 50-125 cGy/h.
The basal size of the melanoma is estimated preoperatively and confirmed during surgery. Appropriately sized plaques are sutured temporarily to the sclera and limbus underlying the melanoma. A margin of 2 mm over the largest tumor basal dimension is adequate. Intraoperative techniques, such as transillumination or ultrasonography, are used to ensure proper plaque placement under the tumor.
Postoperative imaging confirmation of correct plaque localization is required. Radioactive plaques are left in place for 3-7 days. The goal of successful treatment is to achieve arrest of tumor growth or regression in size.
Local recurrence, usually requiring enucleation, occurs at a rate of about 12-16%. Plaque brachytherapy can cause complications, including cataract, rubeosis, scleral necrosis, keratopathy, radiation retinopathy, and optic neuropathy, but at a reduced rate compared with external beam irradiation.
A multicenter randomized trial from the COMS Group that addressed conservative management revealed that patient survival after treatment of medium-sized melanoma is similar when plaque radiotherapy is compared with enucleation. [15]
-
Color photograph of a dome-shaped choroidal melanoma.
-
Early fluorescein angiogram of choroidal melanoma showing intrinsic vascularity.
-
Late fluorescein angiogram of choroidal melanoma showing early diffuse staining.
-
B-scan ultrasound showing acoustic hollowing and uveal excavation in posterior choroidal melanoma.
-
A-scan ultrasound of choroidal melanoma showing low-to-medium internal reflectivity.
-
B-scan ultrasound showing acoustic hollowing in intraorbital extension of a posterior choroidal melanoma.
-
T2-weighted MRI showing a small anterior choroidal melanoma in the left eye.
-
Transpupillary photograph showing a posterior choroidal melanoma.
-
Photograph showing an enucleated eye with advanced choroidal melanoma with transscleral extension.
-
Histologic section of an enucleated eye showing a large dome-shaped choroidal melanoma.
-
Histologic section of an enucleated eye showing a medium-sized mushroom-shaped choroidal melanoma with associated exudative retinal detachment.
-
Choroidal melanoma. Histologic section showing spindle A cells in a uveal nevus.
-
Choroidal melanoma. Histologic section showing spindle B cells in a uveal melanoma.
-
Choroidal melanoma. Histologic section showing epithelioid cells in a uveal melanoma.
-
Photograph showing a skin metastasis of a posterior choroidal melanoma.
-
Intraoperative photograph showing placement of a radioactive plaque for posterior choroidal melanoma.
