What Is CT Lung Cancer Screening?

What to expect when undergoing this test

Lung cancer screening is recommended to monitor for the development of lung cancer in people at high risk of the disease. It involves an imaging technique known as low-dose computed tomography (LDCT), which can help detect cancer in the early stages when it is still highly treatable. LDCT lung cancer screening is a preventive test not intended for everyone and has limited value in people younger than 50.

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

Purpose of Test

Lung cancer is a disease for which too many people are diagnosed when the disease is advanced. Even with increased cancer awareness, nearly 70% of people with small cell lung cancer and 40% of those with non-small cell lung cancer are diagnosed with stage IV 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.

A 2016 study published in Lancet Oncology concluded annual LDCT lung cancer screening detected lung cancer in 6% of the participants (86% of whom were men) in whom new nodules were found on the screening LDCT.

Are You a Candidate?

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

  • Between the ages of 50 and 85
  • 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.

There are no absolute contraindications for LDCT lung cancer screening among eligible candidates. As with all radiotherapy procedures, the benefits and risks should be weighed prior to the test and every effort 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 ascertain whether annual screening in other population groups would have any impact on survival times.

Risks and Contraindications

Computed tomography (CT) is a diagnostic imaging technique in which multiple X-ray images are captured and composited in the computer to create three-dimensional "slices" of internal organs and structures.

As with X-rays, LDCT screening exposes you to ionizing radiation, albeit at lower doses than those used for traditional CT scans. Although studies have shown LDCT is 20% more accurate in diagnosing lung cancer than a chest X-ray, the annual exposure to radiation does pose potential health concerns.

Cancer Risk

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

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

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.

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 one of 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 and costly follow-up procedures, such as bronchoscopy and thoracotomy.

Given that heavy smokers over 50 are at an extremely high risk of lung cancer compared to the general population—anywhere from 64 to 111 times higher—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 LDCT screening, your doctor will schedule the procedure either at a hospital or an independent radiology unit.

There are no pre-tests required before the scheduled appointment, 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. You do not even need to get changed as long as the clothing on your chest does not contain metal. However, LDCT scans do not affect any metal implants in any part of your body, including pacemakers or artificial joints.

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, work with your doctor to gain coverage for the procedure from your health insurance company. You should not proceed until you have preauthorization, since, 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, but the Centers for Medicaid and Medicare Service came out against covering LDCT in 2015, citing that "evidence isn't sufficient" to support its use.

During the Test

LDCT lung cancer screening is not unlike traditional CT scans, although it is usually quicker and doesn't involve as much set-up time.

The test employs a device called 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, in coordinated "slices."

You will be asked to hold your breath as your body is passed through the gantry. The radiation therapist 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 doctor. If LDCT was used for lung cancer screening, the radiologist will make notations regarding whether any abnormalities were found.

LDCT cannot diagnose lung cancer, but can inform the doctor of any changes in the lungs, including the appearance of masses or nodules. By testing annually and comparing past images with current ones, subtle changes can often be spotted.

If an abnormality is found, your doctor may order additional tests. This may include a positron emission tomography scan that uses radioactive tracers to detect metabolic changes consistent with cancer, such as the formation of new blood vessels around an active tumor (angiogenesis).

If the abnormal growth is well-delineated, a biopsy using either fine-needle aspiration, bronchoscopy, or laparoscopic surgery may be ordered.

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

When to Stop Screening

For people who qualify for LDCT screening, the test should be scheduled annually, ideally at the same imaging unit. 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 with each and every year you are off cigarettes.

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