Emory University School of Medicine's Department of Radiation Oncology has become one of the first cancer treatment centers in the world to use a unique combination of imaging and treatment technologies from Varian to treat a case of gall bladder cancer with highly precise image-guided radiotherapy (IGRT). Their approach was designed to compensate for tumor motion due to the patient's normal breathing during treatment -- often a barrier to using radiotherapy in the treatment of thoracic cancers.
The sophisticated treatment combined the use of Varian's On-Board Imager™ device for automated, image-guided patient positioning, with Varian's RPM™ Respiratory Gating for synchronizing treatment with the patient's respiratory cycle.
"The patient is a 68-year-old male," said Jerome Landry, M.D., professor of radiation oncology at the Atlanta, Georgia-based hospital. "The challenge to us was to irradiate the tumor bed after the tumor was removed surgically from the gall bladder, to destroy any remaining cancer cells. But the gall bladder area is right next to the small intestine, which cannot tolerate much radiation. And to further complicate matters, the whole area moves as the patient breathes."
Traditionally, in order to ensure that they are hitting a moving target, radiation oncologists have had to treat a significant amount of healthy tissue around the tumor site. This has made it difficult to use radiotherapy to treat moving tumors in the abdomen.
To prepare the patient for his image-guided radiotherapy, a gastrointestinal surgical oncologist implanted radio-opaque clips into the tumor bed during surgery. Clinicians then used four-dimensional CT scanning to reveal how the patient's anatomy moves over time while he breathes.
"We were able to see the point in the patient's breathing cycle where the tumor was furthest away from the sensitive small intestine," said Dr. Landry. "We then planned to deliver the treatments only at that point in the patient's respiratory cycle." Next, the Emory team positioned the patient for daily treatment using a similar imaging strategy that tracked respiratory motion.
Varian's On-Board Imager™ device, a fully robotic imaging system, was used in conjunction with the respiratory gating technology to track the tumor motion and position the patient for treatment. "This is key; it's the first time we've ever integrated respiratory gating with on-board imaging", explained Timothy Fox, Ph.D., chief medical physicist who assisted Dr. Landry with the treatment. "We used the gating system to make the tumor 'stand still' for us. We used the On-Board imager device to get a look at the implanted clips and move the patient into the proper position for treatment."
Fox pointed out that, before they had an On-Board imager device, clinicians had to position patients for treatment based on tattoos or other external marks on the surface of their skin. "It's nearly impossible to deal with a tumor that is moving under the skin, using marks on the skin surface," he pointed out. "But the implanted clips are right at the target. Using the On-Board imager, we can see them, so we know exactly where to aim. We were able to demonstrate that the clips were really moving, and that we could use gated images to match them up correctly at the right phase of respiration."
According to Lawrence Davis, M.D., chairman of Emory's Department of Radiation Oncology, this treatment was a step on the way to treating tumors outside the brain with a technique called stereotactic radiosurgery. "Stereotactic radiosurgery involves delivering a very high radiation dose in just one treatment session. It has been used successfully to treat tumors in the brain, which do not move around," Dr. Davis explained. "We're showing that we can deliver a dose directly to a target -- even a moving target -- using modern IGRT technologies. We hope to take what we have learned and expand on it so that we can begin to offer patients stereotactic radiosurgery for tumors outside the head."
Emory University School of Medicine is ranked among the nation's finest institutions for biomedical education. Its three-part mission encompasses teaching, scholarship, and service. Emory's School of Medicine is an integral component one of the nation's leading health systems, Emory Healthcare, and is affiliated with the world-renowned Emory University Hospital, located in Atlanta, Georgia, USA. Since 1915, Emory University has been at the forefront of medical knowledge and research, pioneering many of the procedures that have changed the face of medical history.