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.