What Is CT Lung Cancer Screening?

What to expect when undergoing this test

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Low-dose computed tomography (LDCT), a.k.a. CT lung screening, is an imaging technique that uses a rotating X-ray beam to generate several detailed pictures of the lungs. These are composited on a computer to create three-dimensional "slices" that can be viewed and checked for abnormalities.

CT lung screening is a preventive measure that can help detect lung cancer in the early stages, when it is still highly treatable. It is recommended for people who are considered to be at high risk for the disease.

LDCT is not intended for everyone. In particular, it has limited value in people under age 50.

A patient undergoing a CT scan.
Morsa Images/Getty Images

Purpose of Test

Lung cancer is often diagnosed when the disease is advanced. Even with increased cancer awareness, nearly 70% of people with small cell lung cancer (SCLC) and 40% of those with non-small cell lung cancer (NSCLC) are diagnosed with stage 4 disease.

This is the most advanced stage, in which the malignancy has spread to distant organs. Due to late detection, the one-year survival rate for these individuals is only around 19%.

Annual LDCT lung cancer screening is used to improve these odds in people who have no symptoms of lung cancer but are at high risk of the disease.

While it cannot diagnose lung cancer, it can inform your healthcare provider of any changes in the lungs, including the appearance of masses or nodules. This would prompt further diagnostic testing.

Research published in Lancet Oncology in 2016 concluded that annual LDCT lung cancer screening detected lung cancer in 6% of study participants in whom new nodules were found with a screening LDCT.

Are You a Candidate?

According to the U.S. Preventive Services Task Force (USPSTF), CT lung screening should only be performed in adults:

  • Between the ages of 50 and 80
  • Who have at least a 20 pack-year history of smoking (defined as the number of packs of cigarettes smoked per day multiplied by the number of years smoked)
  • Who currently smoke or have quit in the past 15 years

Individuals must meet all of the above-listed criteria for the test to be considered appropriate. If you do, there are no absolute reasons that would prohibit CT lung screening from being performed.

As with all radiotherapy procedures, the benefits and risks should be weighed prior to the test. In addition, every effort should be made to deliver the lowest effective dose.

If you don't meet the criteria but want to be screened, consider that USPSTF experts contend that screening in your case may pose more harm than good. Further research is needed to determine whether annual screening in other population groups would have any impact on survival times.

Metal implants in the chest (like pacemakers) or back (like rods in the spine) can interfere with X-rays and lead to poor quality CT images of the lungs. People with these types of implants should not be screened with CT scans for lung cancer.

Risks

LDCT screening exposes you to ionizing radiation, albeit at lower doses than those used for traditional CT scans.

Although studies have shown CT lung screening is 20% more accurate in diagnosing lung cancer than a chest X-ray, the annual exposure to radiation does pose potential health concerns. Chief among these is the risk of cancer.

Cancer Risk

It is well known that high-dose radiation can cause a number of adverse effects, including tissue injury, birth defects, and secondary cancer. With CT lung screening, however, the effective dose used—roughly 2 millisieverts (mSv)—is far less likely to cause cancer.

According to the Food and Drug Administration (FDA), radiation doses of 10 mSv (roughly the dose delivered with traditional CT scans) are associated with a 1 in 2,000 risk of cancer. That is far lower than the 1 in 5 risk of cancer in the general population.

That is not to suggest that there is no risk associated with LDCT. However, the benefits in high-risk individuals almost universally outweigh any concerns.

For younger people, the cumulative exposure to radiation over the course of years remains unknown, which is why LDCT lung cancer screening is currently not advised for them.

False-Positive Results

For a screening test to be adopted, it needs to be both sensitive and specific. This means that it needs to deliver a high degree of both true positive and true negative results.

With LDCT lung cancer screening, studies have shown that false positives are common, with only 1 in every 20 positive diagnoses turning out to be cancer. Real-world testing suggests the rate may be even higher, hovering closer to 98.5%, according to a 2017 study from the Veteran's Health Administration.

This can expose a person to not only stress but unnecessary, costly, and invasive follow-up procedures, such as bronchoscopy and thoracotomy.

Given that heavy smokers over 50 are at 64 to 111 times greater risk of lung cancer compared to the general population, the risk of false positives is greatly overshadowed by the benefits of early diagnosis.

The same cannot be said for younger people or those at low or moderate risk of lung cancer. For these individuals, LDCT screening may be counterproductive and potentially harmful.

Before the Test

Once you are confirmed to be a candidate for CT lung screening, your healthcare provider will schedule the procedure either at a hospital or an independent radiology unit.

You do not have to undergo any tests in advance of LDCT, although you will need to sign a consent form and fill out a medical information sheet once you have checked in with your ID and insurance card.

LDCT lung cancer screening is a relatively simple exam. It takes less than a minute to perform, and no medications or needles are used.

You can eat before and after the test.

The radiation dose is calculated beforehand using a complex algorithm that factors in the length of the dose, the part of the body being scanned, and other measures.

The cost of LDCT screening can vary by the facility and location, although it tends to fall within a $300 to $400 range.

If you decide to pursue LDCT screening and have health insurance, work with your healthcare provider to get the test covered by your carrier. You should not proceed until you have preauthorization; if you do not receive it, you may end up having to pay the full cost out of pocket.

Under the Affordable Care Act, LDCT lung cancer screening should be fully covered as an essential health benefit. However, the Centers for Medicaid and Medicare Service came out against covering LDCT in 2015, citing that "evidence isn't sufficient" to support its use.

You can take a quiz on the American Lung Association's website to help determine your eligibility.

During the Test

The test uses a helical (or spiral) CT machine, which consists of a movable flatbed and a large donut-shaped gantry.

Once you are laid on the flatbed, it is passed through the gantry as the CT scanner rotates around the body to take continuous X-ray images. This is unlike traditional CT scans, in which individual images are taken, one after the next.

You will be asked to hold your breath as your body is passed through the gantry. A radiology technician will monitor the procedure from behind a protective screen. The entire imaging process takes less than 10 seconds to perform.

Once the scan is complete and the technician confirms that the image is OK, you will be allowed to leave.

LDCT lung cancer screening does not involve any medications or contrast dyes. It is also not associated with side effects.

After the Test

It usually takes a couple of days before the radiology report is returned to your healthcare provider.

If an abnormality is noted, your healthcare provider may order additional tests. This may include:

If no abnormalities are found, you may be advised to get screened again in roughly 12 months' time.

By testing annually and comparing past images with current ones, subtle changes can often be spotted.

When to Stop Screening

For people who qualify for CT lung screening, the test should be scheduled annually, ideally at the same imaging location for consistency's sake. However, there may come a point when screening may no longer be recommended or useful under certain conditions.

The USPSTF currently recommends discontinuation of LDCT screening when a person either:

  • Turns 81
  • Has not smoked in 15 or more years
  • Develops a health concern that makes lung surgery impossible
  • Is unwilling to undergo lung surgery if cancer is diagnosed

A Word From Verywell

LDCT screening is an important tool for the early detection of lung cancer in high-risk individuals but should not be considered a replacement for smoking cessation. No matter how many years you have smoked, quitting can dramatically reduce your risk of cancer over time.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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