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A Novel Method for Determining Optic Nerve and Disc Location for Eye Plaque Treatment Planning

S Scarboro1*, M Astrahan2, (1) University of Virginia, Charlottesville, VA, (2) University of Southern California, Los Angeles, CA

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
To present a novel method for accounting for optic nerve and disc location in CT-based patient specific eye models used for episcleral plaque brachytherapy treatment planning.

Methods:
Current CT-based eye models are generated in Plaque Simulator (Eye Physics, LLC) using three orthogonal reconstructions of the orbit. These reconstructions help determine the macroscopic size and shape of the eye for building a patient-specific model, and additional reconstructions are used to model tumor size and location. 3D modeling enables the calibration of fundus photographs and calculation of coordinates for plaques suture eyelets. Modeling defaults to the assumption that the optic disc is centered on the geometrical axial bisector of the eye. However, we have observed that in many instances the connection of the optic nerve to the sclera is not centered on the geometrical axial bisector, resulting in larger positional uncertainties.

Results:
An additional CT (or MRI) coronal reconstruction passing through the posterior sclera (0.5mm posterior to the posterior pole) can be used to image the location where the optic nerve connects to the sclera of the eye. The location of the nerve, as well as the sheath diameter, can then be modeled by projecting the intersection of the 3D model onto this reconstruction and interactively adjusting disc elevation, azimuth, and nerve sheath diameter. Elevation angles of a couple of degrees are commonplace, and occasionally we have observed elevations up to 10 degrees.

Conclusion:
The Plaque Simulator software is designed to improve the accuracy of plaque placement by providing precise suture position coordinates. The described method further improves the patient-specific eye model by appropriately accounting for optic nerve size and location with the expectation of providing more precise suture coordinates, better prediction of plaque collision with the nerve sheath, and more accurate calculation of dose to the optic nerve and disc.

Download ePoster [PDF]

Funding Support, Disclosures, and Conflict of Interest: Melvin Astrahan is CEO of Eye Physics, LLC

Keywords

Eye Plaques, Brachytherapy, Treatment Planning

Taxonomy

Not Applicable / None Entered.

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