New accelerator design promises cost-effective proton therapy

Proton therapy installations can run into the tens of millions of dollars, as they require whole buildings to house bulky and sophisticated equipment. But an innovative idea, presented July 26 at the American Association of Physicists in Medicine meeting, could bring this capability to virtually any radiation treatment center.

Thomas Mackie, cofounder and chairman of the radiation therapy company TomoTherapy in Madison, WI, presented a proton-therapy design based on a relatively small device known as a dielectric wall accelerator (DWA). Currently being built as a prototype at the Lawrence Livermore National Laboratory in Livermore, CA, the DWA can accelerate protons as much as 100-million electron volts over a distance of about a meter. A 2-meter DWA could potentially supply protons of sufficiently high energy to treat any tumor, according to Mackie, including those buried deep in the body. Yet the device would be small enough to fit in a conventional radiation treatment room.

In addition, a DWA-based proton therapy system would be extraordinarily flexible. It could vary both proton energy and proton-beam intensity, thus eclipsing even the most advanced proton treatment centers, which cannot simultaneously adjust these variables.

Such an accelerator is essentially a hollow tube with walls that consist of a good insulator, a so-called dielectric insulator. When most of the air is removed to create a vacuum, the tube can structurally withstand the very high electric-field gradations necessary for accelerating protons to high energies in a short distance.

The accelerator's small size and its capability to vary energy and intensity could lead to "intensity-modulated proton therapy," the proton version of x-ray-based intensity-modulated radiation therapy now being adopted at treatment centers around the world.

Going from the prototype now being built at Lawrence Livermore to clinical trials could take five or more years, according to Mackie. But if the DWA approach proves feasible, protons may eventually represent a more effective and widely adoptable option for treating cancer.