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
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
"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.