In the treatment of cancer, an ideal radiation source would deliver a near-uniform dose to the target and nothing outside it. This paragon is unachievable. The next best thing would be a source that delivers most of the dose within the target volume and relatively little outside it. In a seminal 1946 article, 1 Robert Wilson recognized that charged particles such as protons come close to accomplishing this highly desirable goal. Spurred by his vision, researchers at a number of centers throughout the world have been evaluating therapies based on protons and other light ions for the past four decades. 2,3
The research has largely been done in physics laboratories, where the necessary accelerators are already in place. Only recently, prompted by what appear to be very positive clinical results, have protons moved closer to mainstream radiation oncology. A number of hospital-based proton medical facilities are now in use or...
