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

Abstract

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.

Salvage/Adjuvant Brachytherapy After Ophthalmic Artery Chemosurgery for Intraocular Retinoblastoma

“…One of the earliest and most extensive investigations reports saving 62% of 71 eyes from enucleation, 67 of which had failed before EBRT (6). Similar ocular survival rates were confirmed by the same physicians, and other groups subsequently quoted ocular survival percentages for eyes treated previously with EBRT ranging from 52% to 89% (17, 19-22, 24). As treatment trends shifted, plaques were also used to secondarily treat or to salvage eyes that had failed systemic chemotherapy.…”

Radiotherapy for ocular tumours

“…17 An anterior inactive extension to custom-built plaques facilitates the positioning for tumours in the posterior pole of the eye (Figure 9). 18 The dose used with Ru-106 plaques in Essen is 80 Gy to the apex, although most tumours responded with a dose of at least 50 Gy. 19 There is no comparative dosimetry of I-125 and Ru-106 and there appears to be a disparity in the doses used.…”

Improved iodine-125 plaque design in the treatment of choroidal malignant melanoma.

“…If optimum shielding is to be obtained 'standard' plaques cannot be used because of variations in tumour size and height and the variable relationship of tumour to the optic nerve, macula, lens, and ciliary body. The position of the tumour is drawn on a model eye with coordinates marked on it as described by Stannard et al 19 The manufacture of the gold backing and returned edge is similar to that described previously.26 The returned edge prevents radiation being emitted sideways from the plaque. This reduces the dose to adjacent normal tissues provided the edges are straight and the seeds are placed adjacent to the edge (Fig 1).…”