Plaque Radiotherapy is one of the most common methods used for treating malignant melanoma involving the inner coats of the eye (uveal melanoma). It is available as a treatment for both small and medium size melanomas, and allows the patient to keep the eye which has been affected by the melanoma. This usually results in an appearance that is cosmetically better than an artificial eye, and allows the patient to keep at least some useful vision in the treated eye.
The commonest type of plaque used at the Royal Adelaide Hospital contains a radioactive substance known as Ruthenium-106. There are two different sizes of plaque (15 mm in diameter and 20mm in diameter), and the size used depends on the diameter of the melanoma inside the eye.
The plaque is applied to the outside of the eye during a short operation, and is left in place for a number of days. During this time, the plaque emits radioactivity from its front surface, which lies directly over the site of the melanoma within the eye.
The plaque is inserted at one operation and is removed at a second operation, usually three to six days later. The time that the plaque needs to stay in place depends on a number of factors, including the height of the tumour (measured by ultrasound examination before the operation), the age of the plaque and the dose of radiation to be given.
The insertion is usually carried out whilst the patient is asleep under a general anaesthesia, and takes between one half and one hour to complete. The outer coat of the eye (sclera) overlying the melanoma is exposed and the exact location of the tumour is carefully marked before the plaque is sutured to the sclera.
The removal is again usually carried out under a general anaesthesia and takes only 10 minutes to complete. Between the two operations you will need to remain in hospital. There will naturally be some discomfort, particularly in the first 24 hours following the operation, but you should not experience significant pain. The nursing staff on the ward will make sure that optimum pain relief will keep you as comfortable as possible.
Your Stay in Hospital
Whilst you are at the Royal Adelaide Hospital for plaque radiotherapy, you will be an inpatient on Ward B6 for the duration of your treatment. B6 is the ward designed specifically for patients undergoing radiotherapy, with nursing staff that are highly trained in this field of medicine.
Following the Operation
Unless the plaque is being removed late in the evening, you should be able to return home later in the day after you have recovered from the anaesthetic. Following your discharge from hospital, you will need to place an antibiotic drop (eg. Chlorsig) and a steroidal anti-inflammatory drop (eg. Maxidex) in the eye four times per day for the next seven days. At the end of this week you will be reviewed by your eye doctor. You will need to continue on the drops three times per day for a further two to three weeks and will be reviewed by your eye doctor again one month following the operation.
Risks of the Operation
The risks of plaque radiotherapy can be separated in to either short term or long term :
Short Term Risks
these are related to the very low risks of the procedure itself and most importantly include infection, bleeding into the jelly of the eye (vitreous haemorrhage) and detachment of the retina, all of which can result in loss of vision or rarely blindness.
Commonly, one of the muscles that moves the eye needs to have its insertion temporarily taken off the eye in order to place the plaque. This may result in double vision (diplopia) which in most cases settles after a week or two when the muscle reattaches itself to the eye, but rarely may be permanent.
Long Term Risks
These are mainly related to damage from the radiation emitted by the plaque whilst it is in place on the eye. Although the eye is not radioactive once the plaque is removed, ongoing damage from the radiation does occur, but its effects on the eye may take many years to be noticeable. All of the radiation related risks are much higher with the Iodine-125 plaque than with the more commonly used Ruthenium-106 plaque.
The risks depend on the location of the tumour in the eye and therefore on the site where the plaque was placed. If the plaque was placed toward the front of the eye, the main risk is of clouding of the lens of the eye (cataract). The cataract can easily be removed at a later date if it is affecting vision or making monitoring of the tumour difficult. If the plaque was placed toward the back of the eye, the most significant risk is loss of vision due to radiation damage to the main nerve at the back of the eye (optic nerve) or to the retina at the central vision area (macula). Loss of vision is not inevitable and it may take many years for the patient to become aware of it. Complete blindness is very rare.
The other important risk is that of continued growth or recurrence of the melanoma. The risk is in the order of 10% and may occur many years after the operation. Because of this risk of recurrence, patients who have been treated by plaque radiotherapy will need to be kept under review for the rest of their lives. It is important to follow up.