News | June 19, 2009

Respiratory Gating for Lung Leaps to Sub-Millimeter Accuracy

June 18, 2009 - Calypso Medical Technologies announced the publication of three new studies investigating the role of the Calypso 4D Localization System in guiding immediate adjustments to radiation delivery in response to tumor motion, a concept known as real-time adaptive radiation treatment.

The three studies were part of a multi-institutional academic and industrial collaboration between Washington University in St. Louis, Stanford University in Palo Alto, Calif., Swedish Cancer Institute in Seattle, Varian Medical Systems and Calypso Medical. The studies appear in the International Journal of Radiation Oncology, Biology, Physics ( The findings indicate that substantial treatment benefits may be realized in the way radiation therapy is delivered for all tumor sites, including fast moving, difficult-to-treat tumors, such as those in the lungs.
These studies include:
"Evaluation of Linear Accelerator Gating with Real-Time Electromagnetic Tracking." Ryan L. Smith, et al. July 2009, vol. 74, issue 3, pp. 920-927.

"Integration of Real-Time Internal Electromagnetic Position Monitoring Coupled with Dynamic Multileaf Collimator Tracking: An Intensity-Modulated Radiation Therapy Feasibility Study." Ryan L. Smith, et al. July 2009, vol. 74, issue 3, pp. 868-875.

"Toward Submillimeter Accuracy in the Management of Intrafraction Motion: The Integration of Real-Time Internal Position Monitoring and Multileaf Collimator Target Tracking." Amit Sawant, et al. June 2009, vol. 74, issue 2, pp. 575-582.

"This research highlights the technical feasibility of integrating the Calypso System with advanced linear accelerator capabilities," according to Dr. Parag Parikh, M.D., assistant professor of radiation oncology and biomedical engineering at Washington University. "The work shows that Calypso electromagnetic tracking can lead to more than just tumor positioning, it can facilitate novel methods of addressing organ motion and can enable highly accurate treatment for moving targets."

The first study, conducted at Washington University and Swedish Cancer Institute, demonstrates how the Calypso System is integrated with the linear accelerator - the equipment used to deliver radiation to cancerous tumors - to gate the radiation beam when the tumor motion exceeded certain thresholds. The ability to automatically to do gating is demonstrated utilizing internal information that reflects how the tumor is moving rather than relying on external markers. Gating the beam based on actual tumor motion improves the quality of treatment that the patient receives and is an important capability that only the Calypso System can provide.

"When tumor motion is left unchecked, it can limit the quality of treatments we can provide. Gating allows us to address motion, reduce the radiation damage to critical structures, and open up the possibility of pursuing novel treatment paradigms like dose escalation," said Dr. David Shepard, director of medical physics at Swedish Cancer Institute.

As Dr. Paul Keall, associate professor and director of the radiation physics division at Stanford said, "The obvious solution is to have the radiation beam follow the moving target. In our multi-institutional work, Calypso tracking measurements were used to redirect the treatment beam in real-time as the target moved."

The other studies conducted at Stanford University and Washington University highlight that Calypso System data can be used to adapt treatment by guiding the multi-leaf collimator - the part of the linear accelerator used to shape the radiation beam - thereby moving it in real time. Tracking the tumor motion based on Calypso System data will enable radiation treatment to be delivered to moving targets with a higher degree of accuracy and confidence. "This technological leap to sub-millimeter accuracy opens new frontiers for radiotherapy and will allow us to rethink both the normal structures spared and targets defined during radiation treatments," said Dr. Keall.

The ability to track tumor motion is a critical component in adapting radiation therapy as it assures the clinician and the patient that radiation is delivered to the cancerous tissue while sparing healthy tissue, thereby decreasing side effects of radiation therapy.

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