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Researchers Pave Way for Tracking of Prostate Motion With a Single kV Imager During Arc Radiotherapy

Thursday, March 4, 2010 Medical PDA News J E 4
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PALO ALTO, Calif., March 3 Researchers in the US and Denmark have made a breakthrough in image-guided targeting of prostate tumors during arc radiotherapy treatments. In research partially supported by Varian Medical Systems (NYSE: VAR), physicists at Stanford University (California, USA) and Aarhus University Hospital (Aarhus, Denmark) have devised a method for 'real-time' tracking of the prostate motion using Varian's On-Board Imager® that shows promise in paving the way for advanced clinical treatments.

Arc therapy techniques such as Varian's RapidArc® technology are fast and efficient radiotherapy treatments delivered in a continuous rotation of the treatment machine around the patient. The position of the target must be updated in real-time in order for the dynamic multi-leaf collimator (DMLC) to track tumor motion. To date, a combination of MV portal images and kV orthogonal images have been tested to achieve this.

"Acquiring mega-voltage images is not ideal during RapidArc because the DMLC can block the view of the target during the treatment," says Per Rugaard Poulsen, lead author of the research. "The kV image beam is not obscured by the treatment DMLC making the markers visible from all treatment angles, unlike with the MV beam."

To test the system, arc radiotherapy was delivered to a 'motion phantom' implanted with fiducial markers while continuously imaging with the kV beam. The target position was determined from these images, acquired from different projections during the arc, enabling the researchers to determine information about its 3D motion. This single imager based DMLC tracking system was shown to have sub-millimeter accuracy for most types of prostate motion. Precise alignment of the treatment beam with the tumor position is vital in radiotherapy treatments, as it can reduce the likelihood of complications due to the treatment.

"The results confirm what has been seen in simulation studies and show that the method is very robust to experimental uncertainties," adds Per Rugaard Poulsen. "We've demonstrated that image-based tracking during arc radiotherapy can be done completely without MV images, which is an important step along the way to image-based tracking during arc treatment delivery."

Corey Zankowski, Varian's senior director of product management, said, "This research paves the way for real-time tracking of the DMLC with tumor motion during advanced arc therapy treatments, which should allow clinicians to reduce treatment margins around the tumor. Varian is committed to working closely with industry experts and researchers to enhance treatment accuracy with the goal of improving treatment outcomes."

An upcoming publication from these researchers will focus on the application of this method to respiratory motion.

Publication: Poulsen et al. IJROBP 2010:76, 914-923

Editorial contact: Neil Madle, Varian Medical Systems, +44 7786 526068

About Varian Medical Systems

Varian Medical Systems, Inc., of Palo Alto, California, is the world's leading manufacturer of medical devices and software for treating cancer and other medical conditions with radiotherapy, radiosurgery, proton therapy, and brachytherapy. The company supplies informatics software for managing comprehensive cancer clinics, radiotherapy centers and medical oncology practices. Varian is a premier supplier of tubes and digital detectors for X-ray imaging in medical, scientific, and industrial applications and also supplies X-ray imaging products for cargo screening and industrial inspection. Varian Medical Systems employs approximately 5,000 people who are located at manufacturing sites in North America, Europe, and China and approximately 79 sales and support offices around the world. For more information, visit http://www.varian.com.

SOURCE Varian Medical Systems, Inc.
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