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Plaque radiotherapy

This treatment is indicated for selected choroidal melanomas, some malignant conjunctival tumours and some tumours travelling to the eye from elsewhere (i.e. metastases). It enables a high dose of radiation to be focused onto a small area and has the advantage of being completed in a few days.

 

The radiotherapy is administered by means of a saucer-shaped plaque, which has an inner, concave radioactive surface and an outer, convex protective shield.

 

Fig5-1

Drawing showing a ruthenium plaque sutured to the wall of the eye overlying a tumour, with an extraocular muscle passing over the plaque.

 

The treatment involves:

  • A 45 minute operation under general anaesthesia, during which the plaque is placed against the wall of the eye directly over the tumour and held in place with sutures.
  • A second 25 minute operation under general or local anaeasthesia. The plaque is removed between one and seven days later, once the appropriate dose of radiation has been delivered.

 

It is possible to select between ruthenium plaques, which are suitable for tumours up to approximately 5 mm thick, and iodine plaques, which can treat tumours up to 9 mm thick (albeit giving a higher dose of radiation to normal ocular structures). Ruthenium plaques are available within a day, whereas iodine plaques need to be constructed for each patient and this takes up to six weeks.

 

This radiation does not travel beyond the eye so there is no risk of hair loss or other general problems. There is no radiation once the plaques is removed.

 

Techniques have been developed for safely positioning a ruthenium plaque eccentrically in relation to the tumour so that we can increase the dose of radiation to the tumour without a corresponding increase in the radition delivered to optic nerve and fovea.

 

 

Fig5-2

 

The photograph shows remnants of an irradiated choroidal melanoma in the left eye (irregular black area), with choroidal atrophy from the plaque extending almost to the posterior tumour margin (i.e., the white area, which is the white wall of the eye that has become visible because the choroid in this area has withered away). The beneficial effects of the radiation extend about 1-2mm beyond the visible choroidal atrophy, so that all the tumour has been adequately treated, despite the ophthalmoscopic appearances. The optic disc and fovea are healthy and ten years after treatment the patient has good visual acuity with no sign of tumour re-growth.