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", stated Jerome Landry, MD, professor of radiation oncology. "The challenge to us was to irradiate the tumour bed after the tumour 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 tumour site. This has made it difficult to use radiotherapy to treat moving tumours in the abdomen.
To prepare the patient for his image-guided radiotherapy, a gastro-intestinal surgical oncologist implanted radio-opaque clips into the tumour 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 tumour was furthest away from the sensitive small intestine", stated 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 tumour 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, PhD, chief medical physicist who assisted Dr. Landry with the treatment. "We used the gating system to make the tumour 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."
Dr. 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 tumour 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, MD, chairman of Emory's Department of Radiation Oncology, this treatment was a step on the way to treating tumours 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 tumours 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 tumours outside the head."
Varian Medical Systems Inc. of Palo Alto, California is a manufacturer of integrated cancer therapy systems, which are treating thousands of patients per day. The company is also a premier supplier of X-ray tubes and flat-panel digital subsystems for imaging in medical, scientific, and industrial applications. Varian Medical Systems employs approximately 3160 people who are located at manufacturing sites in North America and Europe and in its 56 sales and support offices around the world. In its most recent fiscal year ended September 26, 2003, Varian Medical Systems reported sales of $1 billion. More company news can be found in this VMW issue's article Varian's new Trilogy technology for image-guided radiosurgery used at Providence Medical Center in Kansas City.