Eye sparing in high energy X ray beams.

Treatment of cancer of the antrum and nasopharynx often includes the radiation of tissues close to an uninvolved eye. One treatment method consists of using an anterior high energy X ray beam directed to the tumor through the eye. To maintain a high dose adjacent to and behind the eye while reducing the entrance dose to the eye, build-up material is placed on the skin and a tunnel cut through to the eye. When the build-up material is tissue-like, the tunnel can be several centimeters in height and scattered radiation from the tunnel walls will largely offset the build-up properties of the beam. Using higher density build-up material, the dose to the superficial layers of the eye can be reduced almost to the limit set by the open beam characteristics. This technique has been used successfully for 8 years.