The CyberKnife, as the $4 million high-tech machine is called, originally was used to treat hard to reach brain and spinal tumors with radiation. The device also is seen by some doctors as an important advancement in the fight against prostate cancer, the No. 2 cancer killer of men.

Others see it as widening acceptance of a costly technology before researchers have thoroughly evaluated its risks and benefits.

Georgetown University Hospital, which began using the machine in 2001, and other advocates around the country say the CyberKnife offers prostate cancer patients a safe and effective, and much more convenient, alternative to traditional radiation treatment, The Washington Post says.

They say evidence shows the approach is at least as good as standard therapies and that it can prevent unnecessary deaths by making treatment less daunting.

But, many experts fear that it could leave many men unnecessarily vulnerable to recurrences or potentially serious complications.

"It may be better and more convenient," Anthony Zietman, president-elect of the American Society for Therapeutic Radiology and Oncology said. "But it could turn out to be a disaster. No one knows."