CHICAGO, July 2 (UPI) -- A U.S. study provides evidence that computed tomography significantly reduces the death rate due to lung cancer, compared with a chest X-ray, researchers say. The National Lung Screening Trial shows 20 percent fewer lung cancer deaths among trial participants who had the CT scan compared with those who had the chest X-ray. Dr. Eric M. Hart, a radiologist and the NLST Site principal investigator at Northwestern Memorial Hospital, says until now, no screening test for lung cancer has proven effective in detecting tumors at an early, more treatable stage. During the study period, more than 400 individuals were enrolled in the trial in Chicago. "We are extremely grateful to the participants in both the chest X-ray and the CT scan arms who volunteered for this lengthy and challenging trial," Hart says in a statement. "Their continued involvement is the basis for this ray of hope for other heavy smokers." The trial was conducted at 33 sites throu