For years cancer patients have had recourse to a noninvasive surgical technique in which doctors zap tumors with focused beams of radiation. The technology was first used on brain-cancer patients because doctors can easily clamp the head in place, keeping the tumor rock steady. More recently the machines have gotten better at compensating for the patient's movement—from breathing, say—allowing doctors to treat tumors elsewhere in the body. Now doctors at Korea's St. Mary's Hospital are using a device called CyberKnife, made by Accuray in Sunnyvale, California, to treat patients with severe depression and obsessive-compulsive disorder. Other doctors think the technique could be useful to treat Parkinson's and epilepsy patients. Since the radiation creates permanent lesions in the brain, the method is controversial and may take years to win acceptance.