Stop-and-start bursts of radiation are timed to respiratory cycle, enabling specialists to minimize tissue damage while increasing dose
WEST CHESTER, Ohio – Cancer specialists at the Precision Radiotherapy Center are using a new technology to aim precise, high-dose beams of radiation at tumors that move with the breathing cycle without causing unnecessary damage to healthy tissue.
Tumors in the lung and liver, unlike those in the brain or limbs, are not stationary. They move internally as patients breathe in and out. That movement previously forced specialists to treat larger areas around the tumor in order to compensate for the movement, harming healthy tissue in the process, and at times limiting the effectiveness of the radiation treatments.
The new technology, which debuted at the Precision Radiotherapy Center last month, enables radiation oncologists and physicists to synchronize treatment with the breathing cycle. They direct 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 technology is called ExacTrac X-Ray Adaptive Gating and is manufactured by BrainLAB AG. It enables BrainLAB’s standard shaped-beam radiation equipment, known as Novalis®, to work in new ways. The technology was approved by the Food and Drug Administration in late 2003. The term “gating” refers to the specialists’ ability to confine a potent beam of radiation to a defined location.
Precision Radiotherapy is a collaboration between the Mayfield Clinic, the Cincinnati-based neurosurgical practice, and UC Physicians. Both practices are affiliated with the University of Cincinnati (UC).
The respiratory gating technology at Precision Radiotherapy was first used in the treatment of a patient with a metastasis to the liver. The patient underwent 12 high-dose radiation treatments over a period of two and a half weeks.
Tuesday, Jan. 6, 2009
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“The gating technology is a wonderful new tool in our armamentarium,” says David Grisell, DO, Associate Professor of Radiation Oncology 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.”
The benefits of gating technology to patients include 1) a reduction in volume of tissue irradiated and resulting side effects and complications and 2) better outcomes because a higher radiation dose can potentially be focused on the tumor.
“By limiting the treatment to a period of the respiratory cycle, we can limit the radiation area and effects on surrounding tissue,” says Michael Lamba, PhD, a physicist at Precision Radiotherapy and UC.
“When the patient breathes in, the target, or lesion, moves. In a case involving the liver, we 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 we wanted to be sure to hit the lesion, we 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, we can limit our target to a smaller window. We can limit the amount of normal-tissue radiation required to ensure that we’ve hit the tumor with radiation.”
During treatment, the radiation cycles on and off. “We create a radiation ‘window of opportunity’ that encompasses part of the respiratory cycle,” Dr. Lamba says. “The radiation is turned on when the lesion is within the ‘window’ and off when it’s outside.
“We tend to focus on the end of the expiration,” he continues. “People tend to inhale, then slowly exhale, then pause, then inhale. That is the most typical pattern. The end of exhalation is the most reproducible and stable portion of the respiratory cycle.”
X-ray imaging and infrared tracking enable specialists to correlate the internal tumor motion with the patient’s breathing. Specialists monitor the patient’s respiration in real time with the help of external (infrared) markers that are placed on the patient’s chest and abdomen and move up and down as the patient breathes. Internal markers, called fiducials, are implanted near the lesion. X-rays correlate the motion of the fiducials and the target to the motion of the external markers.
“The technology allows us to treat patients in a shorter period of time – in as little as 25 minutes -- and potentially more effectively,” Dr. 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.”
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The Precision Radiotherapy Center offers stereotactic radiosurgery for treatment of tumors both inside and outside the head. Candidates for treatment include patients with benign and malignant tumors of the brain, head, neck, spine, lung, liver, and prostate.
The Mayfield Clinic is recognized as one of the nation's leading physician organizations for clinical care, education, and research of the spine and brain. Supported by 20 neurosurgeons, three neurointensivists, an interventional radiologist, and a pain specialist, the Clinic treats 20,000 patients from 35 states and 13 countries in a typical year. Mayfield's physicians have pioneered surgical procedures and instrumentation that have revolutionized the medical art of neurosurgery for brain tumors and neurovascular diseases and disorders.