The effects of intraocular silicone oil placement prior to iodine 125 brachytherapy for uveal melanoma: a clinical case series

Purpose To investigate the role of silicone oil as an adjunct to iodine 125 ( 125 I) brachytherapy in attenuating radiation dose and reducing radiation retinopathy. Methods A 16-mm COMS plaque loaded with 125 I seeds was simulated in vitro on an eye model containing silicone oil as a vitreous substitute using BrachyDose. The radiation dose ratio of silicone oil vs water to ocular structures was calculated at angles subtended from the centre of the eye. Silicone oil was then used in three choroidal melanoma patients who underwent 23-gauge vitrectomy, silicone oil placement, and 125 I brachytherapy. Results Silicone oil reduced the ocular radiation dose in vitro to 65%. Radiation dose ratios on the retina increased from 0.45 to 0.99 when moving from points diametrically opposed to the plaque’s central axis. In 10–24 months’ follow-up, no patients have developed radiation retinopathy. Each patient required silicone oil removal and experienced cataract progression, and one also developed a retinal detachment. Conclusions This study confirms that silicone oil attenuates radiation dose in vitro , and may protect against radiation retinopathy clinically in patients, however it requires extensive surgical interventions. Further studies in only very selected populations using silicone oil as an adjunct to 125 I brachytherapy will best elucidate its role in shielding radiation retinopathy.