Abstract
Purpose: :
Determination of targeting accuracy and dose verification of the IRay orthovoltage age-related macular degeneration treatment system.
Methods: :
All procedures are identical to those used for actual patient treatments. Ten human cadaver eyes were obtained and placed on a custom fixture on the IRay system, the eye was aligned, and the targeting algorithm was initiated. Radiochromic film was affixed to the posterior portion of the eye. Three X-ray beams were sequentially delivered to overlap on the predicted fovea location as depicted by a treatment spot on the film. A needle was placed through the center of the film and into the eye to register the film and the inner retina. The eyes were dissected to assess targeting accuracy. The dose delivered to the fovea was calculated from the film as well.
Results: :
The average magnitude of the error in needle positions from the actual fovea was 0.6mm +/- 0.4 mm. The predicted dose delivery and the actual dose delivery were nearly identical_6.0 Gy and 5.9 +/- 0.2 Gy, respectively. The average distance between a needle and the optic disc edge was 3.5 mm, leaving 0.5 mm between the edge of the beam and the disc.
Conclusions: :
This study provides confidence that the IRay system delivers X-rays with precision and accuracy. The optic nerve dose is within the limits of safety. With the exception of motion, all major sources of error are included.
Keywords: age-related macular degeneration • retina • radiation therapy