CT Scan Radiation Exposure Risk Much More Dangerous Than Originally Thought.

It turns out that the CT scan radiation exposure risk is much more dangerous than was previously thought.  This is really scary considering how freely CT scans are ordered these days. Come the the ER with a headache shortness of breath or belly pain and your doctor is likely going to have a low threshold to order a CT  scan as a rule out test.   A while back the FDA published a report titled:  What Are the Radiation Risks of CT?   See the table below.

Now it appears these numbers relating to radiation exposure risk  have been severely underestimated due in large part to the higher doses of radiation  being given to patients.  The average CT scan radiation exposure for an abdomen and pelvis exam was not the 8 mSv reported by the FDA, but rather 31millsieverts, with a range of 6 to 90. Ninety millisieverts is equivalent to many thousands of chest X-rays, or the equivalent background radiation of living over a 30 year period.  And you get it all from one CT.

Thirty years of background radiation from one exposure to a CT scan of the abdomen?  That's scary.  With America's obesity epidemic expanding as we speak, higher and higher doses of radiation will be necessary to obtain good looking films.  This can only mean  increasing exposure and risk for potential cancer causing CT scan radiation.

 Table I. - Radiation Dose Comparison

Diagnostic Procedure
Typical Effective Dose (mSv)1
Number of Chest
X rays (PA film) for Equivalent Effective Dose2
Time Period for Equivalent Effective Dose from Natural Background Radiation3
Chest x ray (PA film)
2.4 days
Skull x ray
12 days
Lumbar spine
182 days
I.V. urogram
1.0 year
Upper G.I. exam
2.0 years
Barium enema
2.7 years
CT head
243 days
CT abdomen
2.7 years
1.Average effective dose in millisieverts (mSv) as compiled by Fred A. Mettler, Jr., et al., "Effective Doses in Radiology and Diagnostic Nuclear Medicine:  A Catalog," Radiology Vol. 248, No. 1, pp. 254-263, July 2008.

2. Based on the assumption of an average "effective dose" from chest x ray (PA film) of 0.02 mSv.
3. Based on the assumption of an average "effective dose" from natural background radiation of 3 mSv per year in the United States
Unless otherwise noted, the contents of the FDA Web site (www.fda.gov)--both text and graphics--are not copyrighted. They are in the public domain and may be republished, reprinted and otherwise used freely by anyone without the need to obtain permission from FDA. Credit to the U.S. Food and Drug Administration as the source is appreciated but not required. 
How many cancers are CT scans causing?  Great question.  According to the article "Projected Cancer Risks from Computed Tomographic Scans Performed in the United States in 2007," abstract, Archives of Internal Medicine, Dec. 14/28, 2009, 29,000 cancers will be caused by CT scans performed in 2007 alone, with CT scans of the abdomen and pelvis accounting for just under half of those future cancers. The younger the patient is the  greater their risk of getting cancer as they have more years to develop cancer after CT radiation exposure.  Women were disproportionately affected by the risk (2/3) due to the larger number of scans being performed on them.

Here's one scary figure.  The study authors calculate that a one out of every 270  forty year old women undergoing CT coronary angiography will develop cancer.  These numbers are shocking and leave physicians in a catch 22.  With more and more data now coming out suggesting that CT scan radiation exposure  may significantly increase one's lifetime risk of cancer, physicians are left in a no win situation.  To this data I say wow!

But why?  Why do physicians continue to order so many CT scans?  Some reasons are fear, uncertainty, defensive medicine, easy access and a substitute for good history and physical exam, as this  original Happy Hospitalist ecard so eloquently describes below.

"I've started documenting 'see CT report' for my physical exam.  Just so you know."

I've started documenting "see CT report" for my physical exam.  Just so you know doctor ecard humor photo.

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