Polyethylene-lead tissue compensators for megavoltage radiotherapy.

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.