The use of iodine-125 plaques in the treatment of retinoblastoma.

125I has an energy of 27-35 keV which permits highly effective screening and makes it eminently suitable for treating ophthalmic tumours. It was first used for this in 1974 (Sealy et al., 1976), and since then a flexible system has been developed to treat a variety of such tumours including localized retinoblastoma. A gold foil backed plaque is custom built to cover the tumour(s). The turned edges reduce the dose and thus protect vital adjacent structures such as the optic nerve and lens. The iodine seeds are sealed in the plaque in a predetermined position to give the required dose. A range of doses and times have been used but the authors now aim to give a TDF of 100 to the apex of the tumour in two to three days. Ten tumours in the remaining eye of seven patients with bilateral retinoblastoma were treated. The size ranged from 3 X 3 X 2 to 10 X 10 X 6 mm. There were nine complete responses from 17-90 months and a partial response in one patient who died of metastases at ten months. Vision was maintained in all. Eight recurrent tumours in seven patients were also treated together with a subsequent new tumour in one of the patients. There were three complete responses at 28-39 months and six tumours persisted. Vision was maintained in three of seven patients. The only complication was a vitreous haemorrhage which was mild in two patients, moderate in one patient and severe in three previously treated patients. These latter three patients subsequently had the eye enucleated and were found to have recurrent tumour.