CT SCANS & CANCER RISK

CT (computed tomography) scanners have revolutionized the practice of medicine since they were first introduced into routine clinical practice in 1974.  CT scanners utilize a rotating x-ray device to create hundreds of individual images that can then be reconstructed into a complex three dimensional view of the body by computers.  Current generation CT scanners are able to image the entire human body within seconds, and these high definition images provide physicians with an incredibly detailed view of the organs and tissues deep within us. 

CT scanners have become an indispensible diagnostic tool within virtually every medical and surgical specialty, and an estimated 75 million CT scans are now performed annually in the United States, alone.  As the popularity of these complex and powerful diagnostic imaging machines has continued to grow, so has their use for clinically dubious reasons.  For example, routine scans of the heart, and its coronary arteries, have, increasingly, been used for “screening purposes” in patients without any clinical evidence of heart disease.  Likewise, there has been an explosion in the number of private radiology imaging centers offering fee-based “body scans” for clinically healthy people who are interested in having their internal organs examined for any early signs of diseases that can be detected by CT scans.  Another area of concern regarding the use of CT scanners is that physicians have become so dependent on these machines, and the exquisite images of the human body that they provide, that many (if not most) doctors have a very low threshold to order CT scans as a routine part of their diagnostic work-up of patients.  (For example, in my own specialty of Surgery, the diagnosis of appendicitis is now routinely made with a CT scanner, rather than by the traditional method of the surgeon’s clinical evaluation of the patient.) 

While CT scanners have become essential diagnostic tools, they also expose patients to much higher doses of radiation than most conventional x-ray examinations.    It has long been known that exposure to radiation increases the risk of developing cancer, and that the risk of developing cancer is proportional to the dose of radiation received by patients.  (Based upon recent estimates, it has been estimated that at least 2 percent of all cancer cases may be caused by prior exposure to medical x-rays.)  Moreover, there is no known “safe” dose of radiation in terms of radiation-induced cancer risk.  As if this was not already bad enough, there has been a growing concern regarding the actual dose of radiation that is being delivered to patients from CT scanners across the country, as there is a great deal of variability in the radiation dose settings being used among different CT scan imaging facilities.  (This alarming point was recently brought to the public’s attention when it was revealed that Cedars Sinai Medical Center, a prestigious private hospital in the Beverly Hills area, was being investigated after multiple patients who had undergone CT scans of their brain there began to notice that their hair was falling out.  Authorities subsequently determined that these patients had received grossly excessive radiation doses during their scans.)

Two very important public health studies have just been published in the Archives of Internal Medicine, and the findings of these two related studies have significantly raised the level of concern regarding the current use of CT scanners among public health experts. 

The first of these two studies quantified the amount of radiation dose delivered to 1,119 patients for 11 common types of CT scan examinations that were performed at 4 different hospitals in the San Francisco area.  In addition to calculating the radiation doses received by these patients, the authors also estimated the probable lifetime cancer risk associated with these CT scans.  As the Cedars Sinai case has already shown, there appears to be considerable variability in the amount of radiation used at different institutions to conduct the same exact type of CT scan.  However, the sheer magnitude of this variability in radiation doses, as measured by these researchers, is both mind-boggling and disturbing.  Not only was there an enormous difference in radiation doses associated with performing the same exact type of CT scan between the 4 different institutions that were studied, but significant radiation exposure differences were also present within each individual institution when performing the same type of CT scan examination on different patients.  When the researchers had finished their calculations, they noted an almost unbelievable 13-fold difference, on average, in radiation exposure for the same type of CT scan between the highest and lowest observed radiation doses for each individual type of CT examination. 

Based largely upon cancer incidence data collected after the Hiroshima and Nagasaki atomic bombings, this clinical study’s researchers calculated that an estimated 1 in 270 women who underwent a CT scans of their coronary arteries at age 40 will eventually develop cancer as a direct result of these CT scans (versus 1 in 600 men), while 1 in 8,100 women who underwent CT scans of the brain at age 40 will develop cancer from these scans (versus 1 in 11,080 men).  For men and women who underwent CT scans at age 20 (instead of age 40), the projected lifetime risk of CT scan-associated cancer was nearly double the projected risk of the 40 year-old patients. 

The findings of this study indicate that the variability in radiation exposure between hospitals for the same type of CT scan examination is much greater than was previously believed.  Perhaps even more surprising was the finding that identical CT scan examinations performed within a single hospital also subjected patients to significantly different amounts of radiation exposure.  Finally, the calculated range of radiation exposure for CT scans revealed that, in general, patients are receiving far higher doses of radiation from routine CT scans than has generally been appreciated.  (For example, a single CT coronary artery angiogram delivers the same amount of radiation as 310 chest x-rays!)

The second research study used public health data to estimate the average number of radiation-induced cancers caused by CT scans in the United States.  Based upon current CT scan use, these researchers predicted that approximately 29,000 future cases of cancer could be expected to arise from CT scans performed in 2007 in the United States, resulting in approximately 15,000 deaths due to cancers caused directly by CT scans!

These two studies are eye-openers that should cause all of us, physicians and patients alike, to reconsider the benefits versus the risks of each and every CT scan that is considered before such scans are performed.  Although most CT scans are performed because they offer vitally important clinical information on patients that could only otherwise be obtained by surgical exploration, too many CT scans are still being ordered and performed for far less compelling reasons (one of them being, unquestionably, the tendency of many physicians to order multiple unnecessary tests on patients as part of their practice of “defensive medicine,” in the absence of tort reform throughout most areas of the United States…).  Moreover, the striking variation in CT-associated radiation doses, and the unexpectedly high level of these radiation doses in general, points to the need to improve standardization and compliance at every one of the thousands of institutions in the United States that operates a CT scanner.

As a dedicated cancer specialist, I am already well aware of the potential for radiation-induced cancers, and I have, for many years, tried to be very selective in ordering CT scans on my patients.  In cases where I can gather the necessary clinical information without resorting to radiographic imaging, then I try to avoid obtaining any form of x-ray examination (including CT scans).  In other cases, where I must obtain some sort of imaging examination, then I will often initially use ultrasound or MRI studies in place of CT scans, when appropriate.  Even so, the dramatic findings of these two studies suggest to me that all physicians need to further decrease their routine use of CT scans whenever possible.