Use of a simulator with CT option in radiotherapy of macular degeneration

Purpose: To assess the accuracy of a conventional simulation procedure in radiotherapy of age-related macular degeneration. Methods and Materials: A computed tomographic (CT) extension attached to the treatment simulator was used to acquire CT images immediately after conventional simulation in 18 patients referred for treatment of age-related macular degeneration. Analysis was performed on 16 one-sided treatment cases for whom images were obtained. Error was estimated by the displacement between the observed treatment isocenter and the intended isocenter based on reconstructed eye geometry. Results: Based on single slice measurements, the mean error amplitude was 2.3 mm (range 0.2–5.6). Based on three-dimensional eye globe reconstruction, the mean error amplitude was 2.8 mm (range 0.8–5.3). An incidental finding previously unreported was the lower image quality at the center of the simulator-CT image acquisition field. Conclusions: Small but significant errors from conventional simulation were noted. The integrated simulation-CT procedure may help correct the errors to improve the accuracy of simulation setup. The lower image quality at the center of image acquisition field requires adaptation of the simulation-CT procedure.