A new machine that produces highly energized protons could make proton-radiation therapy more easily accessible to cancer patients. The machine, being developed by researchers at Lawrence Livermore National Laboratory, will be a fifth of the size and cost of the proton-therapy machines that are currently found at six specialized medical centers in the United States.

The smaller, lighter, and cheaper machine should be easier for smaller hospitals to buy and install. That will make proton therapy available to more people. When the device is ready for the market, it will "probably be the world's most sophisticated radiation-therapy machine available at a very affordable price," says Ralph deVere White, director of the UC Davis Cancer Center, which supported early research on the device. "It will change the bar for what is standard therapy."

Radiating tumors with protons has proved to be better than conventional x-ray radiation for treating certain types of cancers, such as head and neck, lung, and prostate. Proton beams can be controlled very precisely, so they spare healthy tissue around tumors and cause fewer side effects in patients. But current proton-therapy machines, owing to the large magnets that create the energetic particles and the concrete walls that are needed to shield the radiation, take up a room the size of a basketball court. The machines also come with a hefty price tag--between $150 and $200 million.

The new machine, called a dielectric wall accelerator, should fit inside conventional radiation-treatment rooms. The goal is for hospitals to replace x-ray machines with the new proton-radiation machine, says George Caporaso, a physicist who is leading the research at Lawrence Livermore.

Caporaso and his colleagues expect to have a small version of the device ready by the end of this year, and a full-scale prototype within the next three years. The machine will be clinically tested at the University of California Davis Cancer Center. If tests succeed, TomoTherapy, based in Madison, WI, will market the machines.

To kill tumors, protons need to have energies of around 250 million electron volts. That requires speeding them up, which is done using a high electric field in machines called accelerators. Accelerators can be made of metal tubes that are tens of meters long, through which particles travel to gain energy. Proton-therapy machines use a type of accelerator called a circular accelerator, which bends the particle beam so that the particles go on a spiral path while gaining energy. Bending the proton beam requires large magnets that can weigh hundreds of tons.