Subretinal and Retrolaminar Migration of Intraocular Silicone Oil Detected on CT.

BACKGROUND AND PURPOSE: Intraocular silicone oil injection has been used to treat complicated retinal detachments, and recently its retrolaminar and intracranial migration has been reported. The purpose of this study was to document the prevalence of posterior migration of intraocular silicone oil on head CT and describe the clinical and radiologic findings. MATERIALS AND METHODS: This retrospective study included 57 patients with intraocular silicone oil injection who underwent unenhanced head CT between November 2008 and July 2018. All images were visually evaluated for subretinal and retrolaminar migration of intraocular silicone oil involving the anterior visual pathway (optic nerve, optic chiasm, and optic tract) and the ventricular system. Attenuation values of those structures were measured and compared with those of the contralateral or adjacent normal structures. RESULTS: We detected subretinal and retrolaminar silicone oil migration in 7 of the 57 patients (12%), noting silicone oil at the optic nerve head (n = 2), retrolaminar optic nerve (n = 5), optic chiasm (n = 3), optic tract (n = 3), and in the lateral ventricles (n = 1). Attenuation values of the structures with silicone oil migration were significantly higher than those of the control regions (optic nerve head, 69.2 ± 12.4 vs 29.8 ± 10.2 HU, P < .001; retrolaminar optic nerve, 59.9 ± 11.6 vs 30.9 ± 8.6 HU, P < .001; optic chiasm, 74.2 ± 11.0 vs 25.6 ± 6.9 HU, P < .001; optic tract, 70.1 ± 4.7 vs 28.7 ± 7.2 HU, P < .001). No significant ophthalmic or neurologic complications were documented in the patients with silicone oil migration. CONCLUSIONS: Subretinal and retrolaminar migration of intraocular silicone oil is common. Although there were no apparent complications associated with silicone oil migration, the radiologist and clinician should be aware of this phenomenon.

SU-E-T-474: Monte Carlo Phase Space Production to Model Magnetically Scanned Proton Beams for IMPT.

PURPOSE: Accurate dose predictions in proton beam therapy using magnetically scanned beams are highly dependent on the accurate modeling of the lateral dose profiles. This study was performed to provide proton phase spaces for Monte Carlo simulations, used to accurately simulate doses at distances up to 12 cm from the central axis of the beam. METHODS: Measured lateral dose profiles at various depths in water were compared to Monte Carlo simulations of doses for 90 discreet initial proton energies. Phase spaces were produced using a one dimensional energy distribution, and a combination of several two dimensional spatial and directional distributions. Simulations were performed iteratively using variations in the initial phase space distributions to achieve acceptable agreement between measured and simulated lateral dose profiles, i.e. differences in FWHM < 0.5 mm and dose differences less that 0.1% at distances up to 12.5 cm. RESULTS: 90 phase spaces of proton sources for different initial beam energies were created for use in Monte Carlo simulations of scanned proton beam therapy patient plans. At a depth of 2 cm in water, the simulated and measured FWHM of the lateral dose profiles differed in in-plane direction by an average of 0.05 mm, in cross-plane direction by 0.13 mm. All simulated profiles were within 0.1% of the measured doses at distances between 2cm and 12.5 cm from the central beam axis. CONCLUSIONS: A library of 90 phase space files has been created to accurately simulate magnetically scanned proton beams for IMPT, providing accurate dose distributions up to 12 cm distance from the central beam axis. This project is supported in part by P01CA021239 from the National Cancer Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health.