What is ocular brachytherapy?
Ocular melanoma, by far the most common type of cancer found in the eye, has a survival rate of about 50 per cent. That might seem strangely low. The cancer’s deadly character stems from its access to the bloodstream. Many cancers move through the body via the lymphatic system but, since that network doesn’t extend inside the eye, ocular melanoma travels through the bloodstream, which does reach the eye. For yet-unknown reasons, it often metastasizes in the liver, at which point mortality is all but certain.
For much of the 20th century, modern medicine’s technique for preventing this was as primitive as it was effective: removal of the eye, called enucleation. While the idea might seem crude in the age of modern technology, enucleation produced the best survival rate for ocular melanoma. Plus, artificial eyes can provide a surprisingly good facsimile for the empty socket post-surgery.
And then in the 1990s, medical research revealed the power of ocular brachytherapy.
Radiation kills tumours, but it also destroys other tissue. The problem of applying its power precisely to a malignant tumour and not to adjacent healthy cells prevented conventional beam-radiation therapy from replacing enucleation as the dominant treatment for ocular melanoma. But enucleation means the total removal of the eyeball, which most people feel a figurative and literal attachment to.
The ideal solution is the precise application of radiation to tumours and not to surrounding tissue, and this is what ocular brachytherapy allows. Radiation hits the tumour and almost nothing else. Plus, 60 per cent of patients retain some kind of vision in the treated eye. Because it’s super-precise radiation and not chemotherapy, patients don’t even lose eyelashes from the treatment, never mind whole heads of hair.
The therapy achieves this by placing the source of radiation on the eyeball itself. Medical physicists prepare radioactive “seeds” of iodine, covered in plastic and silicon and embedded in a gold disc. A surgeon hand-sutures the disc onto the white of the patient’s eye at the precise location where the radiation will damage the tumour. The optic nerve has between five and eight millimetres of slack in it, which allows the eye to be rotated for this suturing. Fine control limits radiation damage to the healthy parts of the eye, and the dense gold prevents it from leaking into the delicate and squishy circuitry of the brain. The procedure requires a second surgery to remove the disc after around a week.
(Article by Lewis Kelly, printed in LEAP – Alberta Cancer Foundation 2012, click here to read the whole article)
The CALGARY EYE FOUNDATION is pleased to help patients with some travel costs as they undergo ocular brachytherapy treatment.
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