SEATTLE, July 25 -- 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(TM) 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.

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