People who have smoked a pack of cigarettes every day for at least 30 years should get advanced lung scans annually starting at age 55 to check for early evidence of cancer while it’s still treatable, researchers said.

Low-dose computerized tomography may cut the risk of dying from lung cancer by 20 percent, according to a report presented today at the American Thoracic Society International Conference and published in the Journal of the American Medical Association. For every person diagnosed with lung cancer, there were 20 with suspicious findings that needed biopsies or other follow-up to rule out a malignancy, the researchers said.

The risk of cancer is great enough in heavy smokers 55 to 74 years old to justify annual CT scans, according to guidelines from the American College of Chest Physicians and the American Society of Clinical Oncology based on the study results. They aren’t recommended for older and younger smokers, people who quit more than 15 years ago, patients with limited life expectancies or those who light up less frequently.

“Low-dose computed tomography screening may benefit individuals at an increased risk for lung cancer, but uncertainty exists about the potential harms,” said researchers led by Peter Bach, from Memorial Sloan-Kettering Cancer Center in New York. Because most patients are diagnosed with advanced disease, there is renewed enthusiasm for the CT screening, “which is able to identify smaller nodules,” the researchers said.

Lung cancer is the leading cause of cancer-related death, killing an estimated 160,000 people in the U.S. each year, according to the American Cancer Society.