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Tomotherapy: Making Radiation Therapy More Precise and Target-Specific

Tomotherapy: Making Radiation Therapy More Precise and Target-Specific

Doctors soon may be armed with a new technology that allows them to bombard tumors more accurately--and safely--with larger doses of radiation, thanks to research conducted at the University of Wisconsin Medical School. The new technology may help radiation oncology teams more easily plan the shape, intensity, and direction of radiation beams, and ensure that identical beams are delivered at each treatment session.

The researchers have constructed a bench-top prototype of the new machine and have begun simulation testing. Named tomotherapy, the new approach marries computed tomography (CT) to radiation therapy.

In traditional treatment with linear accelerators (linac), the CT pinpoints exactly where treatment will be aimed and the linear accelerator beams, usually tuned to only one level of intensity, are focused to hit tumors from a few different directions. Though custom-made shields and other "blocking" systems offer some protection, the radiation can harm surrounding normal tissue.

The new tomotherapy machine combines the two concepts by arranging a linac in a CT-like ring configuration, permitting radiation to be aimed at tumors from all angles around the body.

"Lying on a table, the patient moves through the ring as the linac rotates, emitting radiation beams of varying intensity," explained T. Rock Mackie, PhD, Associate Professor of Medical Physics and Human Oncology at the University of Wisconsin Medical School. Dr. Mackie heads the team that is developing the tomotherapy process. Intensity of each beam is controlled by metal leaves that define beam width by opening or closing veins through which the radiation travels.

One of the biggest advantages of the system may be this ability to vary radiation intensity coming from numerous angles, a feature that ensures that the combined "shape" of the radiation beams conforms precisely to the tumor shape. "Tomotherapy will let us deliver optimal doses to even the most complexly shaped tumors with greater accuracy, helping us spare untargeted neighboring structures," noted Mackie.

Tomotherapy's ring configuration also makes it convenient to mount a CT scanner and a beam imaging system that will let radiotherapists "see" the patient's anatomy as they line up beam positions before each treatment session.

Combining a CT imaging system with a linac, as only the tomotherapy unit does, prevents positioning problems such as organ shifting, weight loss, tumor shrinkage, patient movement, and incorrectly made or positioned shields, allowing lower amounts of radiation to reach undesired destinations.

Mackie expects tomotherapy units should be able to deliver optimal treatment in about the same amount of time needed for treatment with current technology. Once research and development costs are recouped, a tomotherapy unit should cost no more than conventional linacs.

"Tomotherapy's greatest advantage may be its potential to make superior treatments routine, and ultimately less expensive, by requiring less technical staff expertise," he said. Unlike three-dimensional radiation therapy with traditional linacs, it has the potential to be used even at small facilities.

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