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This paper investigates a method of designing and producing an unusual class of compensators. Through use of these compensators one can deliver an even dose to dmax when one is irradiating a sloping contour with a single megavoltage photon field. These compensators are designed not to provide an even dose at midplane in a patient but instead to produce what may conceptually be described as an equal surface dose. (A more accurate but less descriptive term would be equal dmax dose compensator.)

Tissue compensators afford one the opportunity of producing idealized dose distributions in radiotherapy. We have developed a technique which may be used to produce fast, accurate and inexpensive compensators within a few minutes and requires minimal patient involvement. Three dimensional contour data is acquired using a moire fringe photograph taken at the time of simulation. The photograph is projected to the size needed for the actual compensator and a sketch of the compensator is made. The sketch is placed in a specially designed small portable pantographic unit and the design is traced while the unit cuts the compensator from an indexed polyethylene-lead blank which is premounted on an acrylic tray. The polyethylene-lead material proves to have an ideal combination of properties for compensator construction including relatively high density, ease of machining, good handling characteristics and low cost.