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Question:
"An article in the New York Times said I could get cancer from too many CT scans. Is this true?"

Dr. Yoler Responds:
There has been a lot of general information and sensational claims in the news recently about the radiation exposure you receive when undergoing a computed tomography (CT) medical imaging exam. Unfortunately, it is always the most sensationalist numbers that get repeated over and over again.

The study you are referring to equated radiation exposure and effects experienced by many atomic bomb survivors in Japan to present day patients who receive computed tomography (CT) scans. This may not provide a reliable basis for comparison. Most CT exams are performed in a controlled setting which results in limited radiation exposure to a small portion of the body. The atomic bomb survivors experienced instantaneous radiation exposure to the whole body across a full spectrum of radiation—x-rays, particulate radiations, neutrons and other radioactive materials.

CT exams expose patients solely to x-rays. The known biological effects are very different for these two scenarios.

How Safe is CT Medical Imaging?
The probability is very low for getting cancer from over-exposure to the radiation dosages received from CT imaging. Estimates of the cancer-causing capability from x-ray exposure during a CT scan have a broad range of statistical uncertainty.

Recent studies by Dr. Joseph Schoepf, an associate professor of radiology at the Medical University of South Carolina in Charleston, were conducted on a more accurate patient population (male, age 59, average weight of 91 kgs.). These studies revealed that the risk of getting a radiation-induced cancer (1 in 500) is actually far lower than the report being shouted from the rooftops (1 in 114) suggests. Dr. Vicky Goh, a radiologist at the Paul Strickland Scanner Centre, Mount Vernon Hospital, in London recently published similar results.

What Does this Mean to You?
To fully understand the impact of CT radiation exposure on our body, we must first understand that we live in a radioactive world and always have. Exposure to radiation is part of our natural environment. We are continually exposed to radiation from the earth, radiation from outer space, radiation from within our bodies as a result of what we consume and from naturally occurring radiation (radon) in the air around us.

This radiation is normally measured in units called millirems (mrems) in the US and millisieverts (msieverts) internationally. The annual cumulative dosage for an average American is approximately 360 mrems (or 36 msieverts).

Dosages can vary greatly from this amount based on the area of the country and altitude where you live, your occupation, how often and how far you travel by airplane, your body size and what medical procedures you undergo. International standards allow for exposure up to 5500 mrems annually for people who work with and around radioactive materials.

There is little doubt in the medical community that CT scans help save lives. Advancing technology has increasingly allowed imaging exams to replace more invasive techniques, but has also resulted in increased radiation exposure for Americans. This increase should be understood and appreciated, but not feared. It is important to remember that when a CT scan is justified by medical need, the associated risk is small relative to the diagnostic information obtained.

Limiting Patient Exposure to Radiation
Fortunately, the newest CT systems (like the Siemens Sensation in use here at Washington Imaging Services) have an automatic exposure control option that limits the amount of radiation the patient receives based on body size and the area being imaged. This will go a long way in reducing the radiation exposure during a CT exam.

We can also look at replacing CT use, when practical, with other imaging modalities, such as ultrasonography and magnetic resonance imaging (MRI). The cost of an MRI is decreasing, making it more competitive with CT, but currently there are not many common imaging scenarios in which MRI can match the speed and resolution of a CT scan.

Washington Imaging Services shares the belief of the American College of Radiology (ACR) that no medical test, particularly those utilizing ionizing radiation, should be performed unless the medical benefits clearly outweigh any risk associated with the exam. We also support the ‘as low as reasonably achievable’ (ALARA) concept which urges providers to use the minimum level of radiation needed in such exams to achieve the necessary results.

Take Charge of Your Health
We also recommend that you keep a record of your CT scan history and, before undergoing an CT exam, ask your physician the following questions recommended by the American College of Radiology (ACR):

• Why do I need this exam?
• How will this exam improve my health care?
• Are there alternatives that do not use radiation which are equally as good, such as an MRI or ultrasound?
• Is this facility ACR accredited? (This ensures that physicians and staff meet education and training standards and that the equipment is surveyed regularly by a medical physicist to ensure that it is functioning properly.)

For more information regarding radiation exposure from medical imaging exams, WIS urges patients and providers to visit the “Radiology Safety” section of the ACR website: www.acr.org. Also check out the "Radiation Safety” section of www.radiologyinfo.org. This excellent patient information site is co-managed by the ACR and the Radiological Society of North America (RSNA).