Accuray Inc. said Wednesday it received U.S. Food and Drug Administration clearance for a software upgrade of its CyberKnife VSI robotic radiosurgery system that lets doctors plan lung cancer treatments without surgically implanting markers in patients.

The Sunnyvale, Calif.-based company hopes the new feature will benefit patients with inoperable lung cancer who qualify for radiation therapy but for whom the implant surgery is slightly risky.

"It now makes lung treatment with the CyberKnife completely noninvasive," Euan S. Thomson, Accuray's president and CEO, told DOTmed News.

Radiosurgery uses blasts of high-energy X-rays to kill tumors, usually in only one or a few sessions. But treating lung cancer is tricky, as patient breathing can cause tissue to shift. Typically for stereotactic body radiosurgery, doctors implant extremely tiny gold seeds, called fiducial markers. These act as landmarks, visible under advanced imaging scans, to guide the physicians during treatment so they don't expose healthy tissue to radiation.

But implanting the seeds carries a slight risk of injuring the lung, causing it to collapse. Thomson said he didn't have exact figures on the rate at which it occurs but that it's a known challenge for patients and physicians.

He said the company tested the software upgrade partly on a large pool of retrospective data saved from earlier exams and partly with some prospective patients, and that it has comparable accuracy with the metal marker approach.

According to the company's estimates, there are nearly 380,000 lung cancer patients in the United States who could benefit from the treatment. Around 216 CyberKnife units have been installed worldwide as of the end of last quarter, the company said.

Accuray's stocks rose 5.3 percent to close at $6.58 Wednesday.

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