Results from the National Lung Screening Trial of more than 50,000 people at high risk for lung cancer showed that patients who undergo screening with helical low-dose CT scanning are less likely to die from lung cancer. NLST compared low-dose CT screening against screening with chest radiography. From August 2002 through September 2007, researchers assigned 26,722 people to CT screening and another 26,732 to radiography. Participants underwent three screenings at 1-year intervals (T0, T1 and T2). Eligible participants were between 55 and 74 years of age at the time of randomization, had a history of cigarette smoking of at least 30 pack-years and, if they were former smokers, had quit within the previous 15 years. Anyone who had been previously diagnosed with lung cancer, undergone chest CT within 18 months before enrollment, had hemoptysis, or had an unexplained weight loss of more than 15 lb in the preceding year were excluded. The disease-specific death rate was 247 per 100,000 pe