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S. C. Oliver, M. Y. Leu, S. P. Lee, T. A. McCannel; Attenuation of Iodine-125 Radiation With Vitreous Substitutes in the Treatment of Uveal Melanoma. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5146.
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© ARVO (1962-2015); The Authors (2016-present)
To demonstrate attenuation of radiation from Iodine-125 (I-125) to intraocular structures using liquid vitreous substitutes.
Four candidate vitreous substitutes were tested for attenuation using empiric measurement and theoretic calculation. In vitro and ex vivo cadaveric dosimetry measurements were obtained with LiF thermoluminescent dosimeters (TLD) to demonstrate the attenuation effect of vitreous substitution during I-125 simulated plaque brachytherapy. Theoretical dosimetry calculations were based on Monte Carlo simulation.
In a cylindrical phantom at 17 mm depth, liquid vitreous substitutes, as compared to saline, showed significant reduction of radiation penetration (48% for silicone oil 1000 centistokes (cs) (polydimethylsiloxane), 47% for silicone oil 5000 cs (polydimethylsiloxane), 40% for heavy oil (perfluorohexyloctane / polydimethylsiloxane) and 35% for liquid perfluorocarbon (perfluoro-n-octane). Human cadaveric ex vivo measurements demonstrated a silicone oil 1000 cs to saline dose ratio of 35%, 52%, 55%, and 48% at arc lengths of 4.2, 7.6, 10.6, 22.3 and 28.6 mm from the plaque edge, respectively, along the surface of the globe. Monte Carlo simulation of a human globe projected attenuation as high as 57% using polydimethylsiloxane 1000 cs.
Intraocular vitreous substitutes including silicone oil, heavy oil, and perfluorocarbon liquid attenuate the radiation dose from I-125. Cadaveric ex vivo measurements and Monte Carlo simulation both demonstrate radiation attenuation using silicone oil 1000 cs at distances corresponding to vital ocular structures. Attenuation of radiation with silicone oil endotamponade in the treatment of uveal melanoma may significantly reduce radiation-induced injury to vital ocular structures.
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