Melanoma of the eye can be
intraocular (uveal), ocular surface, in the orbit or on the eyelid. There is a
range of possible treatments for uveal melanoma. These include laser
(thermotherapy or photodynamic therapy), radiotherapy (brachytherapy, proton
beam radiotherapy, stereotactic radiosurgery) and surgery (tumour resection or
enucleation).
Plaque brachytherapy is
designed to deliver radiotherapy to uveal melanoma in a controlled way. The aim
is to treat the tumour, and to minimise risks of vision or eye loss. The
Collaborative Ocular Melanoma Study (COMS) described the standard for
brachytherapy using 125-I, defined the size of melanomas and importantly showed
equivalent survival in a randomised controlled trial between brachytherapy
versus plaque radiotherapy for medium sized melanomas.
The American Brachytherapy
Society’s consensus guidelines for the treatment of intraocular tumours suggest
certain parameters. For uveal melanoma the dose prescribed is 70 to 100 Gy to
the tumour apex. The prescription isodose line should encompass the entire
tumour. Dose rates should not be less than the COMS historical standard of 0.60
Gy/hour. Isotope choice is limited by the size of tumour, with 106-Ru plaques
for tumours less than 6mm height. 125-I or 103-Pd can treat larger tumours, but
tumours greater than 12 mm in apical height or 20 mm in base carry guarded
prognosis for retaining useful vision. Alternatives to brachytherapy for unsuitable
cases where the plaque cannot be placed easily or the tumour is too large,
include proton beam radiotherapy, stereotactic radiosurgery or enucleation of
the eye. Failure of brachytherapy can be managed by further radiotherapy
(brachytherapy or proton beam), laser (usually thermotherapy) or enucleation of
the eye.
Plaque radiotherapy is an
established technique for the treatment of uveal melanoma. Many eyes that would
otherwise be lost are treated with this method. The challenge remains to
minimise complications and to save more lives.