By Ramesh Iyer
A mother brings her 5-year-old son to the emergency room because he’s been having nausea, vomiting and abdominal pain for the last 12 hours.
The boy has a fever in the ER and is quite tender in his abdomen upon physical examination. The ER doctor would like the child to undergo a CT scan because she is concerned about acute appendicitis.
Upon arrival to the radiology department the family is greeted by the CT technologist and the radiology resident on call. As the CT technologist is introducing himself to the patient, the boy’s mother pulls the resident aside and asks, “I’m kind of nervous since I’ve read about CT scans causing cancer in children. What are the chances that my son gets cancer from this CT scan?” After the resident hesitates in responding, she continues, “Be honest – am I making the best decision for my child in choosing to have this CT?”
As a pediatric radiologist, scenarios similar to this one occur a few times each month in our practice. This clinical vignette shows two perspectives of fear and uncertainty. The first, more obvious one is by the patient’s mother. Why should she be fearful of her son getting the CT scan? Well, in part, she’s right! CT scans have been linked to causing cancer, and are a major source of radiation in our society. Between 1980 and 2010 the rate of CT use doubled every two years, and CT now comprises 50 percent of radiation from medical imaging despite accounting for only a tenth of the volume of imaging studies. The number of pediatric ER visits utilizing CT has also increased, rendering it more likely than ever before that boys and girls will get one or more CT scans during childhood.
Alongside this increase in CT use is a pervasive fear of radiation within our cultural fabric. Whether it is a comic book superhero that has garnered special powers from radiation exposure, or the occasional threat of nuclear weapon construction and deployment, radiation has become a household topic that, on balance, is perceived negatively. In the last 15 years, several major news outlets have closely linked CT scans with cancer, citing sources from the medical literature. Even the medical literature has fallen victim to using provocative terms such as “threat” and “danger,” or even referring to CT scans as a “public health time bomb.” I believe that the messages regarding radiation risk are based on sound concepts, but often miss the mark on language, resulting in starkly negative connotations and undue anxiety amongst patients and their families.
How about the radiology resident who is addressing the mother’s concerns? Here is the second instance of fear and uncertainty in the vignette. I think discussing radiation risk is among the more challenging aspects of my job. This is, in part, due to a lack of experience and formal training most radiology residencies provide. But I think this is primarily because available data regarding carcinogenic risk at low radiation levels, i.e., those encountered in medical imaging, are relatively sparse and variable. Most of the older data pertaining to radiation causing cancer were extrapolated from Japanese atomic bomb survivors. A handful of larger epidemiologic studies have been published this decade attempting to more precisely quantify the risk of cancer children encounter when obtaining CT scans. While each of these studies has limitations, all of them concluded that the risk of a child getting cancer from one CT scan is low, typically much less than one percent. Many organizations, such as the National Academy of Sciences, the American Association of Physicists in Medicine, and the United Nations have published statements clarifying that risk of cancer from medical imaging is unclear and may be negligible at such low doses. To further muddy the waters, we must also consider annual background radiation, much of which is derived from naturally occurring radon gas found in homes. A child may receive the equivalent dose of at least one CT scan in background radiation each year by merely watching TV, going to school, visiting friends, etc.
Patients today are more educated than ever before. The information available to them, and their desire to be proactive in their care, are both far cries from the heyday of paternalistic medicine in the 20th century. The parents of children in our practice are often well-educated professionals who are familiar with the concept of radiation in medical imaging, have informed questions, and look to us for additional, nuanced information to help them make the right decisions. They often want the radiologist to give them a sense of what the data shows regarding the radiation risk from imaging. It is the responsibility of the radiologist to be an informed consultant who can communicate the risks effectively, is sensitive to the concerns of the family regarding radiation, and partners with the family to decide on the best imaging pathway.
Accurately conveying these risks in both absolute and relative terms, in a way that the patients can understand and appreciate, is the “holy grail” for the radiologist in this setting. There is no correct way to do this, as every person processes information differently. It is often helpful to begin with general statements to not confuse the family with minutia: “the radiation risk posed by this CT scan is very low, if truly present at all.” However, in my experience, patients are more frequently asking for numbers – more precise data to guide their decisions. For example, when consulting with the patient’s mother, the radiology resident in the vignette could incorporate the following:
“The current data regarding risk of getting cancer from the low radiation doses used in medical imaging is currently unclear. For frame of reference, when we refer to radiation in medical imaging, we are typically talking about less than 100 millisieverts (mSv) of cumulative radiation dose in one’s life. The annual background radiation dose is about 3 mSv per year, and this abdominal CT should result in 1-2 mSv when using proper dose reduction techniques. The available data suggests that the additional risk of a child getting cancer from a CT scan lies anywhere between one in 300 to one in 3000 or possibly much lower when such techniques are used. This tiny additional risk is very difficult to identify upon a background of one in four people dying from cancer naturally.”
The final point in the above paragraph highlights the use of relative risk when discussing radiation. When discussing risk using a statement like “one in 300 chance of getting cancer,” the radiologist must realize that the patient’s caregiver might only be hearing “my child will be that one who gets cancer.” Many hospitals illustrate the relative risk of radiation-induced cancers in creative ways. For example, one children’s hospital created a patient handout describing this as follows: given that the lifetime rate of cancer in all children is about 700 in 3000, if an infant receives a CT scan of the belly, then this rate might increase to 701 in 3000. Other hospitals have created similar handouts with visual representations of the risk of dying from various illnesses in proportionately sized pie charts. Heart disease and cancer (sporadic) combine to occupy more than half the pie, with the risk of dying from cancer from a CT scan corresponding to a very tiny slice. Other institutions compare the risk of radiation-induced cancer to more apparent risks, such as dying from choking or cycling (~0.1 percent), and far less than the chance of getting killed in a car crash. While such topics are clearly morbid, it can be helpful to translate the nebulous risks of radiation into terms that are more concrete and practical for the patient to relate to.
Finally, it is also critically important to consider all your imaging options. In many cases, another imaging modality may be the more appropriate choice, and in certain instances imaging may not be needed at all to direct patient management. While radiation is certainly a concern with pediatric CT exams, more pressing concerns would be confirming the presence or absence of a contrast allergy and if sedation may be required. In this vignette, performing an abdominal ultrasound to look for appendicitis would be preferable to a CT if experienced sonographers are available. Discussing such options with the family and arriving at a mutual decision will build trust and lead to an improved patient experience.
The pediatric radiologist often faces an uphill battle when communicating radiation risk to patients. Physicians frequently encounter a fear of radiation that has been stoked by embellishments and mixed messages throughout the literature and popular culture. These challenges are compounded by the unclear carcinogenic effects of radiation at the low levels utilized in radiology. Nevertheless, the consulting radiologist should feel obliged to become familiar with the available literature, and skilled at synthesizing this information accurately and transparently. Our patients and families depend on us to be responsible stewards of this knowledge as it emerges in the coming years.
About the author: Dr. Ramesh S. Iyer, M.D., is an associate professor of pediatric radiology at Seattle Children's Hospital, where he is the director of radiology quality improvement. He also chairs the quality and safety committee for the Society for Pediatric Radiology (SPR).