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The American Cancer Society

How Dangerous Are CT Scans?

by Dr. Len November 29, 2007

We have a tendency in this country to assume that advances in health care technology are good, and always beneficial for patient care. 


An article in this week’s New England Journal of Medicine which discusses the possible long term adverse effects from CT scans rightly points out that sometimes we ignore the potential for risks associated with those technologies, at our own peril.


The premise is reasonably straight forward: CT scans are X-ray devices, and they deliver a substantial amount of radiation when compared to more traditional forms of x-rays.   The problem is that this radiation may cause cancers in some patients. 


The amount of radiation in a single CT scan, according to the authors, is not out of line with radiation dosages sustained by survivors of the atomic bombs dropped in Japan during World War II.  And, from studies that have been very carefully done, we know that there was an increased risk of cancer in those survivors at those doses of radiation.


The authors state that based on comparable risk estimates along with information on CT scan usage from 1991 through 1996, about 0.4% (or 4 in 1000) of all cancers in the United States may in fact be related to radiation from CT scans.


Given the fact that there has been a surge in the use of CT scans, the authors also state that in their opinion in the future 1.5% to 2% of all cancers may be caused by radiation exposure from CT scans.


The issue isn’t so serious for someone who is older, since cancers that could result from CT scan-related radiation exposure would take years to develop. However, given the fact that there is increased use of CT scans in the pediatric population, this could be a problem since these children will be alive for many years after a scan is performed.


The authors’ concerns are further heightened because, as they write in the article, “if it is true that about one third of all CT scans are not justified by medical need, and it appears to be likely, perhaps 20 million adults and, crucially, more than 1 million children per year in the United States are being irradiated unnecessarily.”


Bottom line: the potential risk for a single CT scan in a single person to cause a cancer is very small. 


It’s when you consider the volume of scanning, the frequency of scanning and the number of people exposed to excess or unnecessary radiation that you begin to see what we call the adverse population effects, with an increase in the numbers of cancers spread over many people.


The reality is that we don’t know what we need to know about this risk based on actual studies of large numbers of people who have had CT scans.  Those studies have not been done.


The risks reported in this article are based on studies of the atomic bomb survivors, and there may be many differences between the effects of their exposures and the exposures that occur from CT scans.


Newer CT scanners and technologies enable us to provide high quality images with less radiation.


But, the authors point out that many doctors don’t appreciate the seriousness of the risk from CT scan radiation. 


They report that in a survey of radiologists and emergency room physicians, “about 75% of the entire group significantly underestimated the radiation dose from a CT scan, and 53% of radiologists and 91% of emergency-room physicians did not believe that CT scans increased the lifetime risk of cancer.”


The authors also note that some professional medical organizations are making efforts to better educate their physician members about this issue, especially among doctors who care for children.


How did we get into this situation, and what are the implications for patient care?


First, I can tell you from my own experience that CT scans were an incredible step forward in medical diagnosis and treatment when they were first introduced.  They allowed us to see things we could never see before.


Fast forward, however, and what has happened is that there is a tremendous increase in the utilization of these scans. 


CT scans are obviously found in hospitals and the offices of radiologists.  But they are also appearing in the offices of internists and family doctors, orthopedic surgeons and other specialists.


Doctors are relying more and more on CT scans, and less and less on histories and physicals when it comes to making diagnoses.


Frequently, the use of CT scans is appropriate.  Sometimes it is not.


I am familiar with one situation (I actually had the opportunity to review the medical record, since I couldn’t believe what I heard) where an elderly person with several medical problems saw his doctor for a routine visit.  Among his complaints was a headache he had for several days.  He had no other symptoms.


The doctor stopped the exam, and took him down the hall to the office CT scan.  The scan was done and was normal.


He returned to the examining room, and the doctor continued taking the history (it wasn’t much of a history at that).  No physical, no evidence of any changes in the patient’s condition.  It was simply a substitution of a CT scan for spending the time to talk to and examine the patient.  From my perspective, I couldn’t find a justification for the scan.


I am not saying that this is a routine event in medical practices, but it is becoming more common as the statistics suggest.


The authors of the report note that 3 million CT scans were performed in the United States in 1980.  Currently, the estimates are that more than 62 million scans are performed in this country every year.  And, as I pointed out previously, they estimate that about one third of those scans are not medically necessary.


I must point out that you shouldn’t refuse a CT scan when you have to have one.  They are an incredibly useful tool.


But you shouldn’t have a CT scan without being aware that there are some risks, especially if it is a scan that is not going to impact the course of a diagnostic work-up or influence your treatment.  Getting a CT scan just to get a scan is not a good idea.


With the increased use of CT scans for medical screening (lung cancer, colorectal cancer and whole body scans advertised frequently on radio and television in some markets come to mind), as well as the use of CT scans in diagnosing coronary artery disease (these scans do have a considerable radiation dose), we are certainly going to hear more about this topic.  In fact, I have already participated in discussions where the dose of radiation from cardiac CT scans has been discussed.


Although the situations are not directly comparable, there have been lessons learned about radiation usage in the past.


I remember as a child when I went to the shoe store and they had a machine that let the salesman and my mother see how my feet fit in a new pair of shoes.  Yes, it was an x-ray machine in the shoe store.  I also remember when someone realized this may not be a good idea, and the machines were banned.


Around the same time, using radiation to decrease the size of enlarged tonsils was in vogue as a treatment alternative to surgery.  My parents were offered this treatment when my tonsils became enlarged, and fortunately they declined.  I had my surgery for my tonsils and did fine.  The children who had the radiation have endured a significant increase in thyroid cancer as a result of their therapy.


And, along the way, there have been warnings that have appeared from time to time about the risks of excessive radiation from the usage of routine chest x-rays and other “plain” films.


But CT is replacing the “old fashioned” x-ray for a number of very valid and some not so valid reasons (the reimbursement system is skewed such that physicians are paid much more for the equipment part of the transaction than for taking the time to talk with and examine their patients, but that is a topic for another day).


My physician colleagues also note that the medical-legal climate is such that they feel forced to order CT scans for even vague complaints, even though they know that there is a very small chance of finding something.


I doubt that our appetite for CT scans is going to diminish anytime soon.  Hopefully, over time, we will develop a better understanding of exactly what the cancer risk from these scans really amounts to.


In the meantime, use some common sense.  Ask your doctor whether you really need the scan, and whether it is going to make a difference in your treatment.  Tell your doctor that you understand and you accept the small chance that a CT scan done for defensive medical purposes may show something unexpected, and that you are willing to rely on their judgment and not get the scan. 


Make certain your scan is done on modern equipment and that the machine is set for the lowest radiation dose for your particular scan and circumstance.  Ask whether there is another test—such as an ultrasound—which can provide the same information with less radiation risk.


Always remember that the potential risk from any single scan is very small.  If you need a CT scan, go ahead and get it.


But like everything else we do in medicine, be aware that every test and every medication we use has some risk attached to it. 


The theme we need to embrace, as pointed out by this article, is that in health care, we must always take into consideration not only the benefits of a particular technology but the risks as well.

Filed Under:

Cancer Care | Screening | Treatment


12/3/2007 9:20:47 AM #

Gary Engel

As a media person, I thought the national media did a pretty poor job of presenting the situation with CT scans. Scare tactics seemed to be the rule. I think if more people read Dr. Lictenfeld's submission, they'd feel a lot better about the amazing technology. Risks vs. rewards - life in microcosm.

Gary Engel

12/17/2007 10:51:22 AM #

Dr. Joe Galati

From a physician's standpoint, I agree that many physicians order a CT scan before examining the patient. Patient beware: tell your physician if you have had a recent CT scan. All too often a scan done last month for the same problem is repeated.In most cases, the follow-up CT scan is done "because you are here" and too difficult to get the results from a prior scan. Keep good files on your scans and other diagnostic tests.

Dr. Joe Galati

12/18/2007 10:53:41 AM #

I agree.

2/27/2008 11:44:36 AM #


I would refuse to get a CT scan to the abdominum.


2/11/2009 2:20:17 PM #

John Johnson

How do we know if the CT dose we received was excessive? I was told my annual CT dose was 2-1/2 times the European limit, and am reluctant to repeat that.

John Johnson

2/11/2009 2:51:50 PM #

Len Lichtenfeld

I can't speak to the issue of whether or not your scan dose was excessive, but would emphasize that CT scans should be done only when medically appropriate.  If you have concerns, you should discuss these with your doctor and the radiologist.  These are not "benign" studies, as pointed out in the article.

You commented that this was an "annual scan."  Obviously, I don't know your medical history but I would question why you get a CT scan routinely every year.

Bottom line, be certain that you really need the scan for a very specific medically related problem.

Len Lichtenfeld

5/18/2009 1:17:16 PM #

Mary West

July 3, 2008 - CT scan ordered w/contrast because ofsevere constipation, not eating, bloating.  Reacted to iodine with nausea and wanting to vomit.  Colonoscopy followed the next day - no colon cancer.  Felt great.  However, a few small slightly enlarged lymph nodes showed up in upper small intestine on CT scan.  I had a biopsy, results inconclusive. I had no pain or other symptoms; Oncologist told me to wait 6 weeks and have another CT scan; I waited until September 23, 2008; no change.  Ocologist suggested I have another CT scan in January 2009.  My primary doctor and I decided to wait until May since I have no symptoms and feel great.  Now it is time to decide, and I do not want the radiation danger with having 3 abdominal CT scans in less than 1 year.  Your thoughts please!!!

Mary West

3/1/2010 2:05:40 AM #

john gubelman

Experiencing abdominal discomfort, went to physician, ordered CT Scan of abdomem.  CT Scan results indicated 4mm rounded nodule on right lower lobe of lung. Also slightly enlarged mesenteric lymph nodes in left hemiabdomen. Dr. ordered CT scan of w/ contrast of chest. Had scan without contrast, results pending. Further procedures endoscopy and colonoscopy ordered. Would lymph nodes cause pain in abdomen? What would cause lymph nodes to be enlarged above small intestines? What is proper path to take to find out what's causing my pain?  Is this the right path? If & how many CT scans should I have? Had 2 in 2 weeks. Please advise. Thank you, your comments will be deeply appreciated & taken into consideration.

john gubelman

8/20/2012 12:57:13 AM #


I had an MRI about 2yrs ago that showed I had an anyurisum ,a follow up MRA agreed Then a CTA was ordered and the  same conclusion was deduced. The doctor ordered a follow up CTA the following year that also showed an anyurisum only this time in a different location of the brain than the first....8 mos have now passed an the doctor requested a 3rd CTA to confrim one or both of the anyurisums.I have 2 concerns first if yet another CTA is done how will we know which to believe and second with all this contraversy how reliable are these things and is it worth the radiation exsposure?


10/3/2012 6:24:39 AM #


HI, I'm 27 Year Male,  I just undergo CT SCAN ABDOMINAL and came to know that the people who are doing Abdominal CT SCANs are at higher risk of Cancer... I'm really scared.... Can anyone let me know if this is true ? Do I need to worry about it ? Can I prevent this from happening anyway ??


About Dr. Len

Dr. Len

J. Leonard Lichtenfeld, MD, MACP - Dr. Lichtenfeld is Deputy Chief Medical Officer for the national office of the American Cancer Society.