More Can Be Dangerous: Computed Tomography and Radiation Exposure

Abstract & Commentary

By Alison Edelman, MD, MPH, Assistant Professor, Assistant Director of the Family Planning Fellowship Department of Obstetrics & Gynecology, Oregon Health & Science University, Portland, is Associate Editor for OB/GYN Clinical Alert.

Dr. Edelman reports no financial relationship to this field of study

Synopsis: The radiation dose received in one typical CT scan slightly increases the lifetime risk of death from cancer. The risk is age and site-dependent as children and digestive organs are more radiosensitive.

Source: Brenner DJ, Hall, EJ. Computed Tomography—An Increasing Source of Radiation Exposure. NEJM. 2007;357:2277-2284.

Of note, this publication is a review article and not original science. The use of and possible indications for Computed Tomography (CT) scans have been rapidly growing since its introduction, particularly in the area of adult screening (ie, virtual colonoscopy, CT whole-body screening). Drs. Brenner and Hall have written a comprehensive and very understandable (even to medical specialties outside of radiology!) review article on everything you ever wanted to know regarding CT scans.1 Although CT scans are quick, user-friendly (for both the physician and the patient), and noninvasive, they impart a significant amount of ionizing radiation (10mGy for one abdominal/pelvic CT scan but often more scans are needed to complete one study). Epidemiologic studies have shown that exposure to an average of 20-50mGy of ionizing radiation increases the risk of cancer. The risk is age and site-dependent as children and digestive organs are more radiosensitive.

Commentary

I often have difficulty articulating to my family, friends and patients why more isn't always better and can be, at times, dangerous especially in regard to screening for cancers. Although advancements in science and technology have been a boon to the field of medicine, we aren't there yet with the use of CT scans for cancer screening.

How accurate is the test? Does early diagnosis lead to improved survival or quality of life? Will we do more good than harm? What is the severity and frequency of the disease? Costs of the test, the disease treated or untreated? These are the questions that we as medical professionals should be asking prior to adding a screening test to our current screening armamentarium.2,3 Unfortunately, this is not the same approach our patients use and who can blame them? When offered a choice between a noninvasive test vs a scope up their "nether regions" or testing "#2", what choice would anyone make? But I think we can still make our argument that "more isn't better" with the following:

  1. One must still undergo a complete bowel preparation with virtual colonoscopy.
  2. The colon does not does not virtually inflate with air. The colon needs to be insufflated prior to a virtual colonoscopy (use your imagination).
  3. If something is found on a virtual colonoscopy, a standard colonoscopy is necessary.
  4. You are increasing your risk of death from cancer by screening for it with a virtual colonoscopy through exposure to ionizing radiation.

Now, not to use scare tactics, let me explain this risk of cancer further. The overall risk of cancer and the risk of death from cancer due to exposure to ionizing radiation with a CT scan exists but it is small. The risk is dependent on the average lifetime exposure, the age when exposed, and the body part exposed. For example, exposure to one typical abdominal/pelvic CT scan at age 25 increases your lifetime risk of death from cancer by 0.06%, but that same exposure as a neonate would be 0.14%.1 It is also important to note that the article only gives estimated risks for death from cancer and not the risk of cancer, which would be even higher. These are also estimates based on the exposure to only one typical CT scan. Using CT scans for screening purposes would mean a series of CT scans during an individual's lifetime, not to mention CT scans needed for unplanned diagnostic purposes (car accidents, etc). Personally, I am going to save my lifetime limit of ionizing radiation until I am really going to need it (hopefully, never!).

References

  1. Brenner DJ, Hall, EJ. Computed Tomography—An Increasing Source of Radiation Exposure. NEJM. 2007;357:2277-2284.
  2. Evidence-based Medicine. How to practice and teach EBM. Sackett D, et al. 2nd Edition. Churchhill Livingstone, NY, NY. 2000.
  3. Clinical Epidemiology. Weiss, N. 2nd Edition. Oxford University Press, NY, NY. 1996.