Magnetically scanned proton therapy beams: rationales and principles

High-energy proton therapy is finding increased application in radiation on cology because of the unique physical characteristics of proton beams which allow superior conformation of the high-dose region to the target volume. The standard method of "painting" the required dose over the target volume is to use passive mechanical means involving multiple scattering and variab le thickness absorbers. However, this technique dose not allow proximal sur face dose conformation which can only be achieved using beam scanning techn iques. Apart from reducing the integral dose, intensity modulation and inve rse planning are possible, there is less activation of the surroundings and no field-specific modification devices are required. However, scanning sys tems are very complicated and there are very high instantaneous dose rates which require sophisticated control systems. (C) 2001 Elsevier Science Ltd. All rights reserved.