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."