CT Scans FAQs
- What is Computed Tomography?
- Is the amount of radiation used in CT scans for lung cancer safe?
- What does the CT screening process look like?
What is Computed Tomography?
The CT (Computed Tomography) scan or the CAT (Computer-Aided Tomography) scan is a diagnostic procedure that takes a detailed cross-sectional x-ray picture of a "slice" of the body.
To get a CT scan, the patient lies very still on a table, which is slowly moved horizontally while the x-ray machine rotates around the patient and takes pictures from many angles. A computer then combines the pictures into a very detailed cross-sectional image. The length of the procedure depends on the areas to be x-rayed. For the chest area, the procedure takes about 20 seconds.
CT scans can show the shape, size and the exact location of organs and tissues in any "slice" of the body more clearly than other diagnostic tools. This technique can help find enlarged lymph nodes, which might contain cancer that has spread from the lung. CT scans are more sensitive than routine chest x-rays in finding early lung cancers. CT scans are also used in detecting masses in the liver, adrenal glands, brain and other internal organs that may be affected by the spread of lung cancer.
Is the amount of radiation used in CT scans for lung cancer safe?
Recent articles published in Archives of Internal Medicine, "Projected Cancer Risks From Computed Tomographic Scans Performed in the United States in 2007" and "Radiation Dose Associated With Common Computed Tomography Examinations and the Associated Lifetime Attributable Risk of Cancer" raise concerns about the potential risks associated with radiation. The radiation doses considered in those articles was based on standard dose scans rather than the low dose we currently employ in our research and therefore are substantially higher doses than participants in screening studies are likely to receive.
Nevertheless, they remind us of the need to continually examine our protocols so that we continue to lower the dose we use while still maintaining appropriate image quality. The doses considered in those articles were as high as 90 mSv (millisieverts) for abdominal CT scans and for standard chest CTs as high as 24 mSv with a median of 8 mSv. They did not evaluate scans using the lower doses that we recommend in our research where we strive for the lowest dose possible, typically 1 or 2 mSv or lower, although for individual patients it may be slightly higher than this value.
As a comparison, average background radiation in the US is approximately 3 mSv/ year and in Denver, Colorado, due to the higher altitude it is 11.8 mSv/year, and the dose allowed to people who work in the radiation field is 50 mSv/ year.
It should also be recognized that the conclusions of these articles are not universally accepted. For example, the American College of Radiology said in a press release that,
"No published studies show that radiation from imaging exams causes cancer. The conclusions of the authors of the Archives’ studies rely largely on data which equates radiation exposure and effects experienced by atomic bomb survivors in Japan to present day patients who receive computed tomography (CT) scans. Most CT is performed in controlled settings and results in limited radiation exposure to a small portion of the body. Atomic bomb survivors experienced instantaneous exposure to the whole body. CT exams expose patients solely to X-rays. Atomic blast survivors were exposed to X-rays, particulate radiations, neutrons, and other radioactive materials. The known biological effects are very different for these two scenarios. Cancer assumptions based on this paradigm should be considered, but not accepted as medical fact.
Also, the articles - after excluding patients with cancer or within five years of the end of life - assumed that those undergoing CT scanning have the same life expectancy as the general population. This is not accurate, so the estimates are undoubtedly high. Moreover, 25 percent of people in the United States die of cancer with a life time incidence of 40 percent, about 1.5 million new cancers per year. The 29,000 [only 4,100 from standard Chest CT] figure, if even close to accurate, is overall a very small risk versus the immediate, proven life saving benefits of CT."
What does the CT screening process look like?
Click each image to enlarge.
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Front View: CT scanner
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Side View: CT scanner
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CT Technician with a patient
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CT screening patient having CT Lung Screen
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CT Technician performs a CT scan
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Experienced Chest Radiologists review CT images
Below are 2 videos that fully describe the CT experience, including an actual CT scan. Click on either to download keeping in mind that the movies are large files (approximately 9-16 MB), and are in the Quicktime format (plugin available free from www.apple.com)
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