Lung Cancer Screening Using Helical CT vs. Chest X-ray Reduces Deaths among Current and Former Heavy Smokers

Computed tomography (CT) scan of the abdomen; drawing shows the patient on a table that slides through the CT machine, which takes x-ray pictures of the inside of the body.

Credit: Teresa Winslow (artist), for NCI

People with a history of smoking have a high risk of lung cancer – a disease with a five-year relative survival rate (for smokers and non-smokers combined) of only 15.8 percent.  Previous attempts at developing a test to find lung cancer early, when it is easier to treat, have not been able to demonstrate a decrease in mortality rates. Now, a study sponsored by the National Cancer Institute (NCI) has determined that low-dose helical computed tomography (CT) scans can reduce lung cancer mortality for current and former heavy smokers.  In the nation-wide study, which included over 53,000 participants, researchers found 20 percent fewer lung cancer deaths among those who were screened with low-dose helical CT (also known as spiral CT) compared with those who were screened with chest X-rays. In addition, deaths from all-causes (including lung cancer) were seven percent lower in those who received the low-dose helical CT scans.

“This is the first time that we have seen clear evidence of a significant reduction in mortality with a lung screening test in a randomized controlled trial.  The fact that low-dose helical CT provides a decided benefit will be a result that will have implications for the screening and management of lung cancer for many years to come,” said Christine Berg, M.D., NLST project officer for the NCI, in a press release.

In September 2002, the NCI launched the largest lung cancer screening study ever conducted.  The National Lung Screening Trial, or NLST, compared the effects of two lung cancer screening procedures, low dose helical CT and chest X-ray, in reducing mortality in current and former heavy smokers aged 55 to 74. Unlike previous trials, the NLST was a randomized control trial, the gold standard in clinical trials. Participants were randomly assigned to one of two comparable groups – chest X-ray or helical CT – and received three annual screenings based on their assigned technology.  The groups were followed for at least five years beyond the final screening. (Read an article in this publication from the launch of the trial in 2002)

“The results of this trial provide objective evidence of the benefits of low-dose helical CT screening in an older, high-risk population and suggest that if low-dose helical CT screening is implemented responsibly, and individuals with abnormalities are judiciously followed, we have the potential to save thousands of lives,” said Denise Aberle, M.D., NLST national principal investigator for ACRIN, in an NCI press release.  “However, given the high association between lung cancer and cigarette smoking, the trial investigators reemphasize that the single best way to prevent lung cancer deaths is to never start smoking, and if already smoking, to quit permanently.”

Low dose helical CT, which was introduced in the 1990’s, uses computer-controlled X-rays to scan the entire chest in about 7-15 seconds during a single, breath-hold. The CT scanner rotates around the person, who is lying still on a table as the table passes through the center of the scanner.

Two images depicting the difference between conventional and spiral CT scans. Conventional CT scans take pictures of slices of the body (like slices of bread). These slices are a few millimeters apart. The newer spiral (also called helical) CT scan takes continuous pictures of the body in a rapid spiral motion, so that there are no gaps in the pictures collected.

(Figure A:) Conventional CT scan. (Figure B:) Spiral CT scan. Credit: NCI Cancer Imaging Program

A computer creates images from the X-ray information coming from the scanner and assembles these images into a series of two-dimensional slices of the lung at very small intervals so that increased details within the organs of the chest can be identified.  Virtually all hospitals and free-standing radiology facilities in the United States now have a helical CT machine, which are routinely used for diagnostics. While some facilities do perform helical CT scans for the purpose of screening for lung cancer, such practice has not been previously supported by evidence and is not currently covered by most insurance providers.

Screening with CT scans comes with its own risks.  Radiation exposure from repeated CT scans can lead to illness, including cancer, and people who get false-positive results may be subjected to unnecessary surgical procedures.   It’s important to note that most abnormalities detected with CT screening are not cancer, even in people who are at high risk.

There are over 94 million current and former smokers in the United States who are at high risk for lung cancer.  In 2010, it is estimated that 222,520 people will be diagnosed with, and 157,300 will die from lung cancer, the leading cause of cancer death in the United States.

More information about the new results of the NLST is available in National Lung Screening Trial – Initial results: Questions and Answers and Fast Facts on NLST.  For more information on lung cancer and screening, please visit our Lung Cancer Homepage.

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