A lung cancer screening trial sponsored by the National Cancer Institute (NCI). In the trial, low-dose spiral CT scans were compared with chest x-rays for their ability to detect lung cancer early. The trial included more than 50,000 participants who were aged 55 to 74 years, were current or former heavy smokers, and had no signs or symptoms of lung cancer. The results of the trial showed that participants who were screened with spiral CT scans had about a 20% lower risk of dying from lung cancer than those who were screened with chest x-rays. Also called National Lung Screening Trial.