SU-E-J-115: Graticule for Verification of Treatment Position in Neutron Therapy

Medical Physics
R Halford, M Snyder

Abstract

Until recently the treatment verification for patients undergoing fast neutron therapy at our facility was accomplished through a combination of neutron beam portal films aligned with a graticule mounted on an orthronormal x-ray tube. To eliminate uncertainty with respect to the relative positions of the x-ray graticule and the therapy beam, we have developed a graticule which is placed in the neutron beam itself. For a graticule to be visible on the portal film, the attenuation of the neutron beam by the graticule landmarks must be significantly greater than that of the material in which the landmarks are mounted. Various materials, thicknesses, and mounting points were tried to gain the largest contrast between the graticule landmarks and the mounting material. The final design involved 2 inch steel pins of 0.125 inch diameter captured between two parallel plates of 0.25 inch thick clear acrylic plastic. The distance between the two acrylic plates was 1.625 inches, held together at the perimeter with acrylic sidewall spacers. This allowed the majority of length of the steel pins to be surrounded by air. The pins were set 1 cm apart and mounted at angles parallel to the divergence of the beam dependent on their position within...Continue Reading

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