A mobile electron linear accelerator, the Mobetron, delivers electron radiation therapy during surgery for cancer in standard operating rooms. “The therapy has demonstrated improved local control and, in many cases, increased survival for a number of disease sites,” says company founder and chief scientist Donald Goer of IntraOp Medical Corp., Sunnyvale, Calif., (intraopmedical.com). “For instance, the device is being used on breast-cancer patients at many centers to provide a more precise “boost” to the tumor bed. Studies demonstrate that, for many women, a single dose delivered during surgery can be the equivalent of six weeks of daily radiation treatment,” he says.

Before the Mobetron, electron radiation therapy involved limited options. “Patients either had to be transported from the OR to the radiation department in the middle of a surgical procedure to receive treatment, or facilities had to construct costly shielded bunkers in operating theaters to house conventional linear accelerators,” he says.

Goer says he had a simple plan for making mobile what is usually a 12-MeV, 18,000-lb electron-linear accelerator with lots of lead for radiation protection: reduce the weight and eliminate stray radiation.

Decreasing weight required trimming trim the size of the accelerator. Conventional accelerators are S-band linacs that operate at 3,000 MHz. The Mobetron operates in the X-band at 9,000 MHz. Because the frequency is three times higher, the radiation wavelength shrinks to one-third the previous wavelength. “The accelerator structure is also one-third the diameter of a conventional unit and all RF-components are also one-third smaller,” says Goer.

In addition, because the accelerator's structure has a smaller diameter, it can be encased in less lead and steel and still contain most of the radiation. “Thus, the Mobetron's leakage radiation is two to three orders of magnitude lower than radiation leakage from a conventional S-band accelerator,” he says.

Improved control eliminates the bending magnet, a component on conventional accelerators, which cuts weight and a major source of stray radiation. “Patented features also allow controlling energy using two small, collinear, accelerator guides. Finally, a fixed collimator can be used in place of the variable collimators used in conventional accelerators. Cylindrical tubes help flatten the beam and protect surrounding normal tissues by focusing the radiation field to only where needed,” he adds.