CyberKnife is a new but fast-growing radiation treatment for prostate cancer, and the chief selling point is that CyberKnife treatments take five days instead of the eight weeks for conventional prostate cancer radiation. But as it turns out, Medicare pays for the CyberKnife treatments in 33 states—but not in 17 others. The disparities result from a policy principl in which officials in Washington leave many reimbursement decisions to the discretion of 15 regional contractors around the country.