Better tumor targeting by improved radiotherapy
Lung and liver tumor, among a few more, have a certain characteristic that makes them different than, for example, brain tumor — they aren’t stationary. That means that they move internally as the patients breathe in and out. By treating the tumor by radiotherapy, doctors were forced to treat a larger area around the tumor itself in order to compensate for the movement, but while doing that, they damaged the healthy cells too. That is about to change.
Researchers from the University of Cincinnati have developed a new technology that allows them to aim precise, high-dose beams of radiation at tumors that move with the breathing cycle without causing unnecessary damage to healthy tissue. The method is based on directing the radiation at the tumor only during a specific time in the cycle — typically after the patient has exhaled, and interrupting the radiation when the tumor has moved out of the targeted area. The ability to confine a potent beam of radiation to a defined location is called “gating”.
“The gating technology is a wonderful new tool in our armamentarium,” said David Grisell, DO, associate professor at UC. “We were very impressed with how much of the liver we could spare in this initial case. The treatment went well. We were able to treat a liver tumor in this particular case that we probably couldn’t have treated otherwise. Without the gating technology, too much of the liver would have been exposed to radiation.”
Michael Lamba, PhD, a physicist, said that by limiting the treatment to a period of the respiratory cycle, they can limit the radiation area and effects on surrounding tissue. That means that when the patient breathes in, the target, or lesion, moves. In a case involving the liver, they know that when a patient inhales, the diaphragm moves lower and pushes the liver down. When a patient exhales, the diaphragm moves up and pushes the liver up. Previously, if they wanted to be sure to hit the lesion, they had to include the margin that includes the full motion of the respiratory cycle, which could mean three to five additional centimeters of length. Using the respiratory gating, they can limit our target to a smaller window. They can limit the amount of normal-tissue radiation required to ensure that they’ve hit the tumor with radiation.
“The technology allows us to treat patients in a shorter period of time — in as little as 25 minutes — and potentially more effectively,” Grisell says. “And, most importantly, it allows us to treat patients whose tumors could not be surgically removed and who otherwise would have no other option.”
The technology is called ExacTrac X-Ray Adaptive Gating and is manufactured by BrainLAB AG.
