Three-dimensional beam scanning for proton therapy

An important goal of radiation therapy is to localize the dose in the target volume. The favorable properties of proton beams, such as a well-determined range and straight penetration through tissues, have been used to develop a three-dimensional beam scanning method. This system consists of a two-dimensional beam scanning system and an energy degrader of variable thickness which are both controlled by a beam monitor that is connected to a minicomputer. A typically conformed dose distribution with the three-dimensional beam scanning system was measured by a specially designed multiwire ionization chamber. The results have shown that the system works satisfactorily and considerably reduces the radiation dose outside the target volume. (orig.)