Plaque radiotherapy

What is plaque radiotherapy?
This involves the delivery of a high dose of radiation to the tumor by means of a plaque, which is a saucer-shaped applicator that is attached to the eye for a short period.

How is it administered?

• The operation can be performed under local or general anesthesia.
  
• The conjunctiva is opened and any muscles overlying the tumor are dis-inserted from the eye.
• The tumor location and extent are identified by shining a bright light into the eye so that the tumor casts a shadow onto the wall of the eye (i.e., 'transillumination'). 
• A transparent 'dummy plaque' is sutured to the wall of the eye so that it overlies the tumor. 
• The position of the dummy plaque in relation to the tumor is checked. 
• The dummy plaque is removed and replaced by the radioactive plaque. There are many different plaques, which vary in size, shape and type of radioactive material (i.e., ruthenium, iodine, strontium, palladium, etc.)
• Any dis-inserted muscles are loosely re-attached to the eye.
• The conjunctiva is closed.
• The time necessary for the tumor to be adequately irradiated is calculated mathematically, according to the age of the plaque and the dose required.
• The plaque is removed between one and seven days later once the required dose has been delivered to the tumor.

What are the indications?

• Choroidal melanoma with a thickness not exceeding 5 mm for ruthenium plaque radiotherapy and not exceeding 10 mm if iodine plaque radiotherapy is administered.
• Choroidal metastases, if external beam radiotherapy is considered inappropriate.
• Retinal angioma, retinoblastoma and vasoproliferative tumor if other methods are unsuccessful. 
• Invisible microscopic disease after surgical removal of intraocular melanoma or conjunctival tumors, such as melanoma, carcinoma and sebaceous gland carcinoma.

What are the contra-indications?

• Optic disc involvement by tumor, unless a notched plaque is removed.
• Diffuse melanoma. 
• Extensive ciliary body melanoma. 
• Extensive extraocular spread.

What are the intra-operative complications?

• Inadequate localisation of tumor.
• Retinal damage when suturing plaque to eye.
• Imprecise re-positioning of extraocular muscle.

What are the post-operative complications?

• Local tumor recurrence if the plaque was not well positioned in relation to the tumor or if the dose of radiation was not high enough to treat the entire tumor thickness.
• Optic nerve damage from the radiation, with severe loss of central and peripheral vision.
• Macular damage from the radiation. 
• 'Water-logging' of the macula ('macular edema') caused by fluid leaking from the irradiated tumor.
• With large tumors, the 'toxic tumour syndrome' can develop, with severe retinal detachment, iris new blood vessels (i.e., 'iris neovascularisation' or 'rubeosis') and high pressure in the eye caused by new blood vessels blocking the trabecular meshwork, which drains fluid from the eye (i.e., 'neovascular glaucoma').
• Cataract if excessive radiation is delivered to the lens.
• Retinal detachment if a retinal tear occurs when suturing the plaque to teh eye.
• Double vision if the muscles are not re-positioned accurately.