New technology uses magnetic fields to focus radiotherapy beams on cancer tumors

Exelar Medical hopes to close in later this year on the commercialization of a product designed to improve the effectiveness of linear accelerators.

The technology, dubbed longitudinal intensity-modulated radiation therapy (LIMRT), would enable safe increases in radiation dosage to tumor cells while also reducing the destruction of healthy tissue, said board chairman and chief technical officer Leonard Reiffel, Ph.D.

IMRT has been implemented increasingly in recent years as a high-performance means of improving the efficiency of accelerators used in radiotherapy. It uses multileaf collimators to focus radiation on tumors in much the same way as a camera aperture directs and controls light. Sophisticated treatment planning software can map the angle of the beam and the shape of the aperture to closely match the shape of the tumor using image overlays obtained from PET and CT scans.

The device being developed by Exelar uses strong magnetic fields in the tumor region to improve the match along and across the radiation beam. In essence, the magnetic field concentrates the highly energized electrons on the tumor. The intensity of the radiation beam can be magnetically modulated to a variety of points and depths by adjusting the magnetic field.

"There is no such thing as good enough in the world of cancer," Reiffel said. "The constant desire of radiation oncologists is to increase the dose to the tumor while limiting the dose to surrounding tissue."

The apparatus, which will be Exelar's first product, is built around a small, pancake-shaped superconducting coil contained within a supercooled vacuum bottle. In studies using the device, dose was enhanced by up to 40% in soft tissue. Even a 5% to 10% dose enhancement is considered clinically important, according to Reiffel.

"With existing technology, once you launch the photons into tissue, they and the electrons they create do what they choose along the beam," he said. "LIMRT changes that situation."

Exelar's device can be used with conventional conformal accelerators or with IMRT and takes advantage of the rapid growth in IMRT. More than 10,000 accelerators are installed worldwide, and as many as two-thirds can be adapted to take advantage of LIMRT, Reiffel said.

"LIMRT is a complement to conventional IMRT," he said. "The idea is simply to properly position a steady, passive magnetic field on the outside of the body during treatment with IMRT or conformal methods."

Based in Chicago, Exelar Medical is an outgrowth of a project begun in 1995 and supported by the National Medical Technology Testbed, a Department of Defense program administered in conjunction with Loma Linda University Medical Center in California. Additional funding was obtained from XLR Medical, whose corporate mission is to support development of the technology underlying the magnetic control of external beam radiation therapy.

Exelar itself was created specifically to bring the LIMRT product to market. The clinical product has been in the works for about five years. The company is in the process of securing about $4 million in funding, an achievement that Exelar president William Houston said is close to being accomplished. Once that occurs and 510(k) clearance is received, the product would be marketed to hospital radiology oncology departments and freestanding radiation oncology clinics.

No other company appears to be investigating this type of technology, according to Reiffel. The bottom line to radiologists is the promise of improved outcomes.

"The significance will hopefully be a better cure rate, fewer side effects, and fewer long-term problems," he said.