CyberKnife radiosurgery for prostate cancer shows 100% PSA response
6 April 2009
Accuray Incorporated (NASDAQ:ARAY) has announced publication of the
results from a prospective clinical study on CyberKnife radiosurgery for
prostate cancer, which was published in the March 15, 2009 issue of the
International Journal of Radiation Oncology*Biology*Physics.
The study, led by Christopher King, MD at the Stanford University
School of Medicine, 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
The authors refer to the findings as "highly encouraging," but remind
readers that longer follow-up is required "to confirm durable
biochemical control rates and low late toxicity profiles."
"The evidence in Dr King's study shows a lot of promise for prostate
cancer patients around the world who are looking for a shorter, less
invasive and more convenient course of treatment," said Eric P
Lindquist, senior vice president and chief marketing officer at Accuray.
"We look forward to seeing longer term results and study outcomes
examining the side effect profile of CyberKnife radiosurgery. Doctor and
patient experience thus far has been very positive."
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
Recent studies have confirmed that the prostate experiences rapid and
unpredictable motion of as much as five millimeters 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, 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
This continual assessment of prostate motion, combined with the
CyberKnife 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.
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 conventional 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.
Another study, led by the Stanford University School of Medicine and
published in International Journal of Radiation Oncology *Biology
*Physics on September 1, 2008, concluded the following in regard to
prostate motion during radiation delivery: "Our study shows the
importance of real-time image guidance and motion-compensation
techniques such as the robotic linear accelerator used in CyberKnife
during hypofractionated prostate radiation treatment.
"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
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