Radiation Risk From CT Scans
Richard C. Semelka, MD Editor's Note:Richard Semelka, MD, is one of the preeminent practitioners of abdominal MRI in the United States and is a frequent contributor to Medscape Radiology..
Hippocrates is credited with the expression "First, do no harm" (ca 460-ca 377 B.C.), which has become the oath of all physicians in their doctoral graduation. The radiology community adheres to the fundamental precept of ALARA (as low as reasonably achievable) in order to limit patients' exposure to harmful radiation."First, Do No Harm": The Present-Day Fallacy.
In recent years, there has been an increased awareness of the rights of patients and their need for information and protection. Despite this, one egregious example in which patients are not provided sufficient information to make informed decisions on their healthcare involves the limited information provided to them on diagnostic imaging tools, including their merits and potential adverse effects. A recent article in the radiology literature describes how patients are generally not informed about the potential deleterious effects of radiation exposure related to undergoing computed tomographic (CT) investigation. Only 7% of patients stated that they were informed about the risks and benefits of the examination, and only 3% reported that they were informed about the increased lifetime cancer risk associated with CT. Referring emergency physicians were also largely unaware that there were any potential harmful effects from the radiation exposure, with only 9% aware of the increased cancer risk. Of even greater concern is the fact that the majority of the radiologists performing the CT examinations considered the radiation exposure of limited concern and were unaware of the amount of radiation delivered to the patient with CT. Only 47% of radiologists were cognizant of the increased risk for cancer associated with CT. The article stopped short of describing a further inadequacy of the information provided, in that the patients were not made aware that alternative, less harmful imaging techniques were available, notably, magnetic resonance imaging (MRI).Why Perform CT When MRI Is Safer -- and Perhaps Better. MRI is an imaging modality that is considerably safer than CT on the basis of a number of factors, of which radiation exposure is perhaps the most serious. In addition, MRI may actually be much more accurate in describing disease. Although MRI is recognized to be superior to CT in a number of organ systems, a recent pivotal article also has shown that screening MRI of the entire body may be as accurate or more accurate than individual "gold-standard" diagnostic investigations of individual organ systems. The accuracy of modern MRI to evaluate the full range of organ systems should cause reevaluation of how different imaging investigations should be used to ensure the welfare of patients and optimize their care.CT Scanning: More Harm Than Good?It is beyond question that radiation delivered by x-ray-based imaging modalities has deleterious health effects.[3-7] The problem is that an exact quantification of these harmful effects is difficult to ascertain -- which explains why physicians in general have not been overly concerned about the radiation related to CT investigation. One prior study, however, described the increased risk of breast cancer in patients who are women who received serial spine x-rays for the investigation of scoliosis, and another study described the increased incidence of leukemia in patients who underwent serial radiographic examination during childhood. One of the most recent of these articles estimates that, per year, diagnostic x-ray use in the United States causes .9% of the cumulative risk of cancer to age 75 in men and women, equivalent to 5695 cases. The US Food and Drug Administration (FDA) estimates that a CT examination with an effective dose of 10 millisieverts (mSv), for example, 1 CT examination of the abdomen, may be associated with an increase in the possibility of fatal cancer of approximately 1 chance in 2000 (http://www.fda.gov/cdrh/ct/risks.html).This statistic becomes even more alarming if one considers the potential public health problem, when one contemplates that 60 million CT scans are performed per year in the United States. The pediatric population represents an especially vulnerable group of patients at increased risk for cancer development secondary to low-level ionizing radiation. Recent studies show that 600,000 abdominal and head CT examinations annually in children under the age of 15 years could result in 500 deaths from cancer attribute to CT radiation. These estimates are terrifying and particularly tragic if safe, alternative radiology modalities are available.Balancing Risks and BenefitsIt has been more than 50 years since physicians had direct physical evidence of the dangers of radiation exposure,[11,12] which is older than the career experience of even the most senior practicing physicians. The understandable excitement that current practicing radiologists experience with the increased imaging capability of modern multidetector CT is therefore not tempered with the direct experience of the harmful effects of excessive radiation exposure. Techniques that employ modern multidetector CT technology, multiphase contrast-enhanced CT of the liver or kidneys, and CT urography are generally performed with the intention of acquiring sufficient data to provide maximal image quality and diagnostic information, but often without enough attention paid to limiting radiation exposure. Attention has been directed in a number of reports to diminish the amount of radiation delivered by CT studies in settings, such as pediatric CT studies or lung screening studies. At the same time, it is clear that often radiation settings are not adjusted to lower levels for pediatric patients and small adults.The Case for MRI: Especially in ChildrenIn my opinion, an even better approach is to avoid radiation altogether by performing MRI. As mentioned previously, consideration is not often placed as to whether another technique may provide equivalent diagnostic information with no radiation risk. The fact that modern CT equipment provides highly collimated beams and adjustable milliamperes may serve to even further lower the level of concern of radiologists and referring physicians to the dangers of radiation, and create the sense that CT is risk-free. Serial CT examinations of patients with various long-standing disorders or chronic disease are especially worrisome.Of particular importance is the pediatric patient, a population in which the radiation exposure is directed to developing organs that are extremely radiosensitive, or breast tissue in women. Examples of this circumstance include patients with Crohn's disease or of childhood abdominal malignancies, such as Wilms' tumor or neuroblastoma.Up to now, MRI has often been thought of as an alternative to CT investigation, either in patients who have contraindications to CT (allergy to contrast agents or poor renal function) or in whom CT findings are considered inconclusive. The prudent approach for the future may be a change in the paradigm of imaging investigation to less harmful techniques, with the preferential use of ultrasound (US) or MRI when accuracy of these techniques is approximately equivalent to CT, and CT reserved as a problem-solving modality and for those indications in which CT is clearly superior. CT is clearly superior for the evaluation of primary lung disease, eg, interstitial lung disease, the majority of chest and abdominal trauma, the evaluation of tubes and catheters in postoperative or intensive care patients, and the search for renal calculi.The majority of benign, malignant, and inflammatory diseases are well shown on MRI, and in the hands of experienced practitioners are better elucidated than on CT, including diseases of the spleen, adrenals, kidneys, pancreas, and male and female pelvis. Patients should undergo CT for indications in which CT is clearly superior, including primary lung disease, acute chest and abdomen trauma, the evaluation of tubes and catheters in postoperative and intensive care patients, and the evaluation of urinary tract calculi.Putting Patients FirstPatients should be made aware of the potential harmful effects of CT, including cancer death, allergic events and renal functional impairment with contrast agents, and possible complications of subcutaneous injection and discomfort with large-bore intravenous catheter insertion. Furthermore, they should be made aware that there are safer alternatives, especially MRI, which may in fact be more accurate for the evaluation of many disease processes.[15,16] Image investigation should also be thought of in terms of and categorized as single-use situations, in which exposure to one CT study may not have substantial deleterious health effects, and those circumstances of which serial use is anticipated, in which case effort should be made to using an alternative imaging strategy, such as MRI. In my opinion, one of the greatest potential harms that exists in patient care today is the injudicious use of CT by many physicians, as they unwittingly subject patients to the untoward effects of ionizing radiation. This is especially unfortunate because often MRI may be employed instead, with greater diagnostic accuracy and greater patient comfort. In diagnostic situations in which the diagnostic information of CT is superior to MRI at the present moment, eg, coronary vessel imaging, CT should be treated as the temporary imaging method of choice, until technical improvements in MRI result in an image quality that approaches the consistent accurate information of CT, and at that time replacing CT with MRI as the primary tool for these imaging indications.If we as healthcare workers are truly effective in our roles as protectors and healers of patients, then we have the obligation to inform them of the risks of radiation exposure and other adverse aspects of CT, and provide them with the information that there are alternative imaging modalities that provide comparable or superior diagnostic information. A common sentiment expressed to me by radiologists is that they would do more MRI examinations for various indications, such as liver investigation, but that they do not have enough MRI scanners to serve all of their patients. My response to them is simple: Invest in more MRI systems for the benefit of patients.In summary, although the exact risks of radiation exposure are difficult to accurately quantify, it is inarguable that radiation exposure is dangerous and undesirable. The use of CT should be used judiciously, especially when safer alternatives, namely, MRI or US, exist for the diagnosis of certain disease processes.Whether MRI or US can replace CT for various indications should be continuously reevaluated, including circumstances in which CT is diagnostically more accurate. US or MRI may evolve to achieve similar diagnostic accuracy. For many neurologic and musculoskeletal applications, the evolution of MRI to replace CT has largely taken place. This same effort should be undertaken in other anatomic regions. In my opinion, the superiority of MRI has already been well established in the liver, to the extent that there is very little indication for the use of CT in liver investigation. In experienced radiologists' hands, many other abdominal and pelvic disease procedures are also better studied by MRI.[2,15,16]Toward a New Way of ImagingIn the present healthcare system, it is ironic that considerable energy and financial investment have been directed toward patient-protection practices, such as HIPPA, with little measurable benefit to the health of the patient, while the health risks of radiation from CT proceed unchecked and a lack of guidelines for physicians and information for patients goes unnoticed.
Medscape Radiology 6(1), 2005. © 2005 Medscape