ASTRO 2012: CyberKnife shows promise in prostate treatments, but more research needed

by Brendon Nafziger, DOTmed News Associate Editor | October 30, 2012
Early results suggest a radiation therapy technique that delivers higher doses in fewer fractions could be a "viable alternative" for men with prostate cancer, according to research shared at ASTRO 2012 in Boston on Tuesday.

The technique promises dramatically shorter treatment times and possible cost savings for payers, but at least one expert warned that the study did not follow patients for very long and that rigorous, longer-term studies were needed.

In the study, researchers from institutions across the country pooling their patient data together found that stereotactic body radiation therapy using the CyberKnife in men with prostate cancer resulted in low rates of disease recurrence a median of three years later. And these rates were possibly lower than with some rival methods, although data from a randomized study are needed in the future, the report's author said.

"This statistic should encourage men to seek SBRT as a viable alternative" to surgery or other radiation treatments, such as brachytherapy and intensity-modulated radiation therapy, author Dr. Alan J. Katz, a radiation oncologist with Flushing Radiation Oncology in Flushing, N.Y., told reporters on a call Tuesday.

The study pooled data on 1,101 patients from Katz's own clinic, as well as eight other facilities, including Swedish Medical Center in Seattle, Beth Israel Deaconess Hospital in Boston, Georgetown University Hospital in Washington, D.C., and UCLA Medical Center in Los Angeles.

The patients were treated with the CyberKnife system, which delivers doses within small margins and performs real-time tracking using fiduciary markers, Katz said. Patients received 35-40 Gy in four to five fractions, many fewer than the 45 or more fractions patients usually get during IMRT schedules, he said.

Patients were then followed for a median 36 months, and close to half were followed for at least four years, according to a slide shown during Katz's presentation.

Katz said actuarial five-year disease-free survival, as measured by rising prostate-specific antigen levels, were 95 percent of low-risk patients, 90 percent for intermediate-risk patients and 80 percent of high-risk patients.

He said these results compared favorably with IMRT, the dominant radiation therapy technique, and added evidence to the view that prostate cancer is sensitive to dose per fraction and higher doses give better results.

"So far all the data we've seen support this," he said.

Interestingly, nearly 150 men in the study received antigen deprivation therapy to reduce testosterone levels, but this treatment had no influence on their outcomes, Katz said.

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