After a patient is diagnosed with Ocular Melanoma, he is referred to the BC Cancer Agency and TRIUMF. The opthalmologist and the radiation oncologist then determine when the treatment should begin, depending on the tumour’s growth speed.
The opthalmologist, Katherine Paton (whose contact details can be found here) assesses the needs of the patient, recommending which treatment would be better: either brachytherapy or proton therapy.
Brachytherapy is an alternative method of radiation treatment for smaller tumours carried out by Dr. Katherine Paton in collaboration with the BCCA. Radioactive seeds are inserted around the tumour, and left in the patient’s eye for about a week or so. This will irradiate the cancer.
Brachytherapy, however, won’t work if the tumour is too big since the seeds won’t penetrate deep enough. Also, this method also won’t be applied if the tumour is close to a critical organ like the optic nerve or optic disc because the seeds would damage these organs.
If the tumour does seem to be too big for Brachytherapy, Proton Therapy will then be the method of treatment.
First, the opthalmologist would perform a minor surgery to attach tiny tantalum clips to the outer surface of the eye to define the boundaries of the tumour. This is performed under general anaesthesia at the Vancouver Hospital and Health Sciences Centre. Its purpose is for the medical personnel to know exactly where the tumour lies, once x-ray photographs are taken. These are then digitized, and a computer model of the patient’s eye, tumour, and clips are created, allowing the opthalmologist, radiation oncologist, and the medical physicist to determine the best treatment position. This includes both the angle of the treatment (where the patient will be looking) and isocentre of the tumour (where the protons will hit).
After a treatment plan has been developed, the energy of the beam is tailored specifically for the treatment of that particular eye. Also, a facial mask and bite block will be made to immobilize the patient during treatment. This ensures that the proton beam will hit only the tumour. Finally, a collimator is also custom made to follow the shape of the tumour. Its purpose is to block the protons that are travelling towards the non-cancer cells.
Once everything is set-up, and ready to go, the patient is ready for treatment. This consists of four identical treatment doses spread out over four days, with each session lasting approximately 90 seconds. Throughout, the patient is asked to look at a blinking light to fix the position of the eye. Breaks will be given if the patient starts to drift off. Also, the patient is allowed to blink, but is still given eye drops to help them minimize blinking.