How Accurate are Low Dose CT Scans for Lung Cancer?

How Accurate are Low Dose CT Scans for Lung Cancer?

Lung cancer is the No. 1 cause of cancer-related death in the United States. Screening with low dose computed tomography (called low dose CT or LDCT) can save lives for people at high risk for this disease.

While effective at detecting lung cancer, LDCT screening carries some risks.

In this article, we discuss the benefits, risks, and accuracy of low dose CT scans for lung cancer detection. We also review who should be screened for lung cancer and how often screening should occur.

Low dose CT scans are the only screening test recommended by the Centers for Disease Control and Prevention (CDC) for the early detection of lung cancer. This test uses X-rays to make cross-sectional images of the lungs and chest lymph nodes. It also uses low doses of radiation to pinpoint tumors in the lungs.

The many detailed images generated by an LDCT can identify nodules or masses in the lungs before symptoms occur. The earlier lung cancer is detected, the better your chances for successful treatment.

As with any screening test, low dose CT is not perfect. It can’t distinguish malignant from benign (nonmalignant) tumors and may not find every tumor. Benign tumors that are found will require further testing that may be invasive.

About false positive test results

False positive results also occur. a 2021 analysis and study to provide updated information about low dose CT screening to the US Preventive Services Task Force found that LDCT screening reduced lung cancer deaths. It also found that the incidence of false positives was significant.

For this analysis, researchers reviewed multiple studies. They uncovered false-positive rates ranging from 9.6 percent to 28.9 percent for initial baseline testing. False positives can lead to emotional distress. They can also lead to unnecessary, invasive surgical testing, which carries additional risk factors.

About overdiagnosis

Another risk of LDCT screening is lung cancer overdiagnosis. Overdiagnosis occurs when tumors are found that will never cause a health issue. This may be because the tumors are indolent (slow-growing). It may also be due to a person’s advanced age or shortened life expectancy for other reasons.

As with false-positive results, overdiagnosis can lead to unnecessary testing and emotional upset.

Chest X-rays are fast and inexpensive. If your doctor suspects you have a disease involving your chest, a chest X-ray will typically be the first requested test.

Pros and cons of chest X-rays

But chest X-rays are not recommended as screening tools. Unlike CT scans, chest X-rays are not useful for finding early, small tumors. They also can’t be used to distinguish between cancerous tumors and other lung conditions, such as a benign lung abscess.

A 2021 retrospective observational study found that the rate of false negatives from chest X-rays for lung cancer was 17.7 percent.

An older multicenter study published by the National Institutes of Health (NIH) found that annual chest X-rays don’t reduce the rate of lung cancer deaths.

Pros and cons of CT scans

CT scans also use X-rays, but the technology differs from that used for a standard chest X-ray. Unlike a chest X-ray that generates one or two images, CT scanners take dozens or even hundreds of pictures. A computer then combines these pictures to show a highly detailed image of your lungs.

CT scans identify more early tumors than chest X-rays can. They’re useful for gauging tumor size, positioning, and shape. CT scans can also identify some cases of cancer spread into chest lymph nodes.

Screening tests for lung cancer can be done annually for eligible high risk individuals.

Diagnostic testing, such as a biopsy, will be done if lung cancer is detected or suspected after a CT scan. Unlike screening tests, diagnostic tests for lung cancer are done only when cancer is suspected.

Other imaging tests may be requested if cancer is strongly suspected or proven via a biopsy, as described in the table below.

The US Preventive Services Task Force recommends an annual low dose CT scan (LDCT) screening for people who meet all three of these criteria:

  • Have a 20-pack-year history of smoking cigarettes. (A pack year is defined as having smoked, on average, one pack of cigarettes daily for 1 year. A 20-pack-year can be defined as either having smoked 1 pack a day for 20 years or 2 packs a day for 10 or more years)
  • Currently smoke or have quit smoking within the past 15 years
  • Are between 50 to 80 years old

Per USPSTF and CDC guidelineslung cancer screening should be discontinued once a person has not smoked for 15 years or develops a health problem that substantially limits life expectancy or the ability or willingness to have curative lung surgery.

People with a history of heavy cigarette smoking are at risk for lung cancer. Lung cancer is the leading cause of cancer death in the United States.

Annual screening for lung cancer with a low dose CT scan (LDCT) is recommended for people at high risk. Your smoking history and age are determinant factors for testing.

Low dose CT scans are the only screening test currently recommended for annual lung cancer screenings. Early detection of lung cancer has been shown to save lives. However, this test is not without risk.

Talk with a doctor about the benefits and risks of annual screening for you.

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