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Erik W. Chell, Mark Arnoldussen, E M. Shusterman, Darius M. Moshfeghi; Assessment of Motion Management in a Stereotactic Radiosurgical Device for the Treatment of Macular Degeneration. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6686.
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The purpose of this study is to evaluate the effectiveness of an automated gating algorithm used during the IRay radiotherapeutic treatment of age-related macular degeneration (AMD) to ensure accurate targeting despite potential substantial patient eye movements. The algorithm was originally designed for use in a Phase I safety study and now recent data from a clinical factors study is used to confirm the design is appropriate for a different population.
The IRay radiosurgical device designed specifically for the treatment of AMD. It delivers three 4 mm-diameter, 100 kVp X-ray beams through the inferior pars plana that converge on the fovea of a non-sedated patient. Targeting is accomplished using a suction-enabled contact lens that stabilizes the eye and allows the imaging system to monitor gaze angle using integrated retroreflective fiducials. Because of the proximity of radiosensitive organs (e.g. lens and optic nerve), targeting must be maintained under patient motion; this is accomplished by an algorithm that permits brief deviations from ideal (e.g. blinks), but gates the beam off in the event of excess error. Motion is logged and the effect on targeting is analyzed. This analysis was initially performed following a clinical trial in Mexico using a prototype device (CLH001, 08/2008-10/2009, 76 subjects). Currently, a clinical factors trial (CHF003) is underway using sham radiotherapy on a device designed for European and US pivotal trials. This trial has enrolled nearly 100 subjects thus far, and data acquisition is ongoing.
The algorithm was designed to maintain the motion-induced positional error to within 400 µm. In the CLH001 subjects, the average positional error was only 170 µm, and in only one patient was the 400 µm goal exceeded (450 µm). The average number of gating events was 1.3 per beam. The analysis of motion from the ongoing CHF003 study will be presented and compared with the Mexican population results.
The gating algorithm designed to protect sensitive structures during the IRay radiotherapy treatment of AMD performs as designed. It ensures adequate targeting under motion while limiting interruptions to a clinically acceptable number. As the IRay therapeutic system becomes more utilized, it is worthwhile evaluating the performance of the device to ensure it meets the original design.
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