SEATTLE, July 25 /PRNewswire-FirstCall/ -- Advanced imaging technology from Varian Medical Systems (NYSE: VAR) is showing great potential for improving the quality of radiation therapy by enabling clinicians to target tumors more accurately and to adapt treatments for tumor motion. Four prominent medical physicists made these observations here at a symposium Varian sponsored yesterday, in connection with the annual meeting of the American Association of Physicists in Medicine (AAPM). Over 350 medical physicists attended the event.
The speakers, Peter Cossmann, PhD, of the Hirslanden Klinik in Aarau, Switzerland; Timothy Fox, PhD, of Emory University in Atlanta; Tinsu Pan, PhD, of the M.D. Anderson Cancer Center, in Houston; and Fang-Fang Yin, PhD, of the Duke University Medical Center in Durham, presented information from their clinical and research experience using a medical linear accelerator equipped with Varian's On-Board Imager™ device to deliver dynamic image-guided radiation therapy (IGRT).
Treating a Moving Target
Peter Cossmann, PhD, and his colleagues at the Hirslanden Klinik in Aarau, have treated fifteen lung cancer patients, using the On-Board Imager device to track the tumor motion due to respiration. "Thoracic tumors do not always move in predictable ways as a patient breathes," Cossmann said. "By using the On-Board Imager in fluoroscopic mode, we're actually looking into the patient just prior to treatment, and we can see how the tumor is moving relative to the planned treatment field."
In treating these lung cancer patients, Cossmann's team used Varian's respiratory gating technology to turn the radiation beam on and off as the tumor moved in and out of range, delivering the dose only at a particular point in the patient's respiratory cycle. They used the On-Board imager to verify that the tumor was, indeed, in the required position whenever the beam was turned on.
Like Cossmann, Tinsu Pan, Ph.D., discussed strategies for treating a moving target. His team is investigating how three-dimensional cone-beam CT images can be correlated with the respiratory cycle. "To effectively treat a moving target, we need to know if tumor motion has changed between simulation and treatment. The On-Board Imager gives us that capability. Without this tool, we really could not do this," he said.
Cone-Beam CT Imaging -- Visualizing Soft Tissues
Fang-Fang Yin, PhD, and his colleagues are also using the On-Board Imager to verify treatments that are synchronized with respiration. Rather than using respiratory gating, they have developed a procedure for using a "breathhold technique" that requires patients to hold their breath for a short period of time during imaging and treatment.
Yin is also conducting experiments to see whether cone-beam CT images of soft tissue structures-including tumors-can be used to verify a patient's position. "We have been taking both radiographic and cone-beam CT images several times a week when setting up patients for treatment," he said. "We're analyzing the data to see if the 3D image enables us to improve our positioning and targeting accuracy. We looked at head and neck and prostate cancer cases, and found that the cone-beam CT images help us to identify patient positioning errors in order to treat more accurately."
In addition, Yin and his colleagues at Duke have been working with the On-Board Imager device on what he calls "cone-beam digital tomosynthesis" (CBDT) -- a faster alternative to cone beam CT imaging for generating 3D images that show soft-tissue contrast.
"Cone-beam CT images are created when we continually generate X-ray images while rotating the On-Board Imager 360 degrees around the patient," Yin said. "With CBDT, we use software to reconstruct a three-dimensional image from a smaller set of images-we need only a 40 degree rotation. The image is not quite as robust as we get with a full 360-degree cone-beam CT, but it is sufficient for identifying subtle anatomical features and localizing the tumor, and it decreases the amount of dose that the patient receives." This promising application of the On-Board Imager device has the potential to make 3D imaging safer, faster and more practical for daily IGRT treatments.
Radiographic Imaging at Emory University
Timothy Fox, PhD, of Emory University presented observations after a full year's experience using the On-Board imager in radiographic mode to fine-tune patients' positions prior to treatment. "We have treated over 257 patients and delivered more than 2800 fractions using the On-Board Imager since June 2004," he said, adding that these have included brain, head and neck, prostate, breast, and gastro-intestinal cancer cases, as well as some pediatric cases. Over that period Fox and his team reduced the time it takes to complete the patient positioning from 7.5 minutes to under four minutes.
The process at Emory involves taking two X-ray images just prior to treatment, and using system software to match them with treatment planning images. The software then calculates how much the patient needs to be moved, to align the tumor properly with the beam. According to Fox, images showed that many patients required positioning shifts. Fox is now analyzing his accumulated data about patient positioning shifts to see if he can find systematic reasons for the displacements.
"The On-Board Imager is helping us quantify patient set-up variances, and we have an opportunity to analyze the data to see if there are commonalities among patients for whom there have been large positioning shifts. Were they all set up using the same type of immobilization devices? Did they lose a considerable amount of weight? Prior to the advent of IGRT, we didn't know the extent of our set-up variances. The On-Board Imager is generating a wealth of information that can help us understand exactly what is going on."
About Varian Medical Systems
Varian Medical Systems, Inc., of Palo Alto, California is the world's leading 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 3,280 people who are located at manufacturing sites in North America and Europe and in its 56 sales and support offices around the world. Additional information is available on the company's web site at http://www.varian.com/ .
Forward Looking Statements
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SOURCE: Varian Medical Systems, Inc.
Web site: http://www.varian.com/