Medical Device Daily

Recent results from a prospective clinical study on Accuray's (Sunnyvale, California) CyberKnife radiosurgery system show that the application has the ability to treat prostate cancer in patients at a much faster rate than other previous applications.

The study, which was started in 2003 and led by Christopher King, MD, at the Stanford University School of Medicine (Stanford, California), treated 41 low-risk prostate cancer patients using CyberKnife radiosurgery. Continual image guidance was used to verify target position throughout the procedure allowing the team to precisely deliver very high doses of radiation in five short treatments.

At a median follow-up of 33 months, no patient experienced a PSA recurrence and early side effects were no worse than other prostate cancer therapies.

Results were published in the March issue of the International Journal of Radiation Oncology Biology Physics also known as the Red Journal.

The authors referred to the findings as "highly encouraging," but they reminded readers that longer follow-up is required "to confirm durable biochemical control rates and low late toxicity profiles."

"This data still needs to be followed further to give a definitive statement that this is the procedure to go to," Omar Dawood, VP of clinical development for Accuray, told Medical Device Daily.

But should data continue to show that this is the go-to treatment, then a patient would be hard-pressed not to select this treatment method.

"You can either travel to a center that offers five to eight weeks' worth of treatment or get the same treatment through the Cyberknife and get it done in five days. It's a no-brainer," Dawood told MDD.

Because the prostate can move unpredictably due to bowel gas or filling of the bladder, it is important that prostate motion is assessed and corrected for throughout treatment to allow for accurate radiosurgery treatment.

Recent studies have confirmed that the prostate experiences rapid and unpredictable motion of as much as 5 mm in as few as 30 seconds, meaning that radiosurgery delivery must recognize and correct for even the slightest motion to ensure the target receives adequate dose and the surrounding sensitive structures, such as the rectum, bladder, urethra and nerves, are maximally spared.

In September 2008, Accuray launched the InTempo Adaptive Imaging System, which enhances the CyberKnife system's ability to continually track and correct for motion of the prostate during treatment.

With the InTempo System, Accuray said CyberKnife radiation delivery automatically adapts to each individual patient's prostate motion by intelligently increasing the imaging frequency during periods of rapid and erratic prostate movement.

This continual assessment of prostate motion, combined with the system's automatic correction for movement in real time, not only helps to ensure prescribed doses are delivered to the prostate; it also helps to ensure surrounding structures are avoided, minimizing associated side effects and complications. Using the InTempo System, the CyberKnife System drastically minimizes the "image age" or time between image capture and when individual beam delivery is complete to as few as 10 seconds.

Accuray said conventional IGRT therapies and other rapid radiation delivery techniques typically provide imaging limited to only pre-treatment set-up and therefore lack the ability to recognize motion that occurs during treatment delivery. With such techniques, there is at minimum a two-minute delay in the time between when the image is captured and the beam delivery is completed.

With an image age of two minutes or more, potential motion that has proven to occur in as few as 30 seconds remains undetected, potentially resulting in inferior targeting accuracy and a heightened risk of surrounding tissue complications, the company said.

Another study, led by the Stanford University School of Medicine and published in the Red Journal's September 2008 issue, concluded the following in regard to prostate motion during radiation delivery: "Given the magnitude and random nature of prostate motion as well as recent technical advancements in various related fields, real-time monitoring of prostate position to compensate for the motion should be part of future prostate radiation therapy to ensure adequate dose coverage of the target while maintaining adequate sparing of adjacent structures."

CyberKnife was created in 1991 and received FDA approval for in-the-body use in 2001. To date it has been used in more than 2,000 patients with prostate cancer and more than 60,000 patients worldwide.

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