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J. Hanlon, E. Chell, W. Smith, W. Bolch; Computational Assessment of Dose for Stereotactic Radiosurgery of Age-Related Macular Degeneration (AMD). Invest. Ophthalmol. Vis. Sci. 2010;51(13):2797.
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AMD is a leading cause for vision loss for people over the age of 65 in the United States and a major health problem worldwide. Research for a new treatment of the wet form of the disease using kilovoltage stereotactic radiosurgery is currently in development. Device design requires patient-specific dose assessment for tissues at risk.
Forty 1-mm axial slice head CT images were acquired from Shands Hospital (IRB #481-2007 University of Florida). Sixteen image sets were selected for 3D reconstruction of patient anatomy and used to evaluate gaze angle and optic nerve tilt with respect to anatomical reference planes (both axial and sagittal). The resulting geometric models were used with the MCNPX 2.5.0 radiation transport code to simulate this treatment. Clinically, treatment is delivered non-invasively by three 100 kVp photon beams entering through the sclera and overlapping on the macula cumulating in 24 Gy of therapeutic dose. Mean absorbed doses and localized point doses were tabulated for the lens, optic nerve, and macula.
Table 1 presents the average of 32 treatment simulations performed on the left and right eyes of each patient. In no case did a tissue at risk receive a mean absorbed dose over the generally accepted threshold for complication. The patient that received the highest point doses during simulation displayed clinically unrealistic gaze (40 degrees inferior with respect to the Frankfurt plane), yet still received mean absorbed doses below the threshold for serious complications.
The computational assessment performed indicates that a previously established therapeutic dose can be delivered effectively to the macula with the scheme described without the potential for visual debilitation.
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