Tomotherapy: Making Radiation Therapy More Precise and Target-Specific

Doctors soon may be armed with a new technology that allows themto bombard tumors more accurately--and safely--with larger dosesof radiation, thanks to research conducted at the University ofWisconsin Medical School. The new technology may help radiationoncology teams more easily plan the shape, intensity, and directionof radiation beams, and ensure that identical beams are deliveredat each treatment session.

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

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

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

"Lying on a table, the patient moves through the ring asthe linac rotates, emitting radiation beams of varying intensity,"explained T. Rock Mackie, PhD, Associate Professor of MedicalPhysics and Human Oncology at the University of Wisconsin MedicalSchool. Dr. Mackie heads the team that is developing the tomotherapyprocess. Intensity of each beam is controlled by metal leavesthat define beam width by opening or closing veins through whichthe radiation travels.

One of the biggest advantages of the system may be this abilityto vary radiation intensity coming from numerous angles, a featurethat ensures that the combined "shape" of the radiationbeams conforms precisely to the tumor shape. "Tomotherapywill let us deliver optimal doses to even the most complexly shapedtumors with greater accuracy, helping us spare untargeted neighboringstructures," noted Mackie.

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

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

Mackie expects tomotherapy units should be able to deliver optimaltreatment in about the same amount of time needed for treatmentwith current technology. Once research and development costs arerecouped, a tomotherapy unit should cost no more than conventionallinacs.

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