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Medical Imaging and Radiation Exposure
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How Safe Is a CT Scan?
There has been a lot of general information and sensational claims in the news recently3 about the radiation exposure you receive when undergoing a computed tomography (CT) medical imaging exam. Unfortunately, sometimes it’s the most ungrounded claims that get repeated over and over again.

The study in question compared the radiation exposure and effects experienced by atomic bomb survivors in Japan to present day patients who receive computed tomography (CT) scans. This may not provide a reliable base 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.

The probability is very small 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 done by Dr. Joseph Schoepf, an associate professor of radiology at the Medical University of South Carolina in Charleston, on a more accurate patient population (male, age 59, average weight of 91 kgs.) revealed the risk of getting a radiation-induced cancer (1 in 500) is actually far lower than the reported incidence of 1 in 114 in the Brenner study. Dr. Vicky Goh, a radiologist at the Paul Strickland Scanner Centre, Mount Vernon Hospital, in London recently published similar results supporting Dr. Schoepf’s lower risk analysis.

What Does This Mean to Me?
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)1.

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, 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.

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 a patient’s 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) 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.

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):

Washington Imaging Services urges patients and providers to visit the “Radiology Safety” section of the ACR Web site as well as the “Radiation Safety” section of www.radiologyinfo.org, the patient information site co-managed by the ACR and the Radiological Society of North America (RSNA), for more information regarding radiation exposure from medical imaging exams.

Average Radiation Doses Associated With Common Imaging Studies
(from the American College of Radiology ©2008)

For this procedure:

Your effective NEJM radiation dose is:

Comparable to natural background radiation for:

Comparable to a routine CXR (PA & Lat) (0.16mSv)

Abdominal region:

Computed Tomography (CT)-Abdomen

10 mSv

3 years

62.5X increase

Computed Tomography (CT)-Body

10 mSv

3 years

62.5X increase

Computed Tomography (CT)-Colonography

5 mSv

20 months

31.3X increase

Intravenous Pyelogram (IVP)

1.6 mSv

6 months

10 X increase

Radiography-Lower GI Tract

4 mSv

16 months

25X increase

Radiography-Upper GI Tract

2 mSv

8 months

12.5X increase

Central Nervous system:

Computed Tomography (CT)-Head

2 mSv

8 months

12.5X increase

Computed Tomography (CT)-Spine

10 mSv

3 years

62.5X increase

Myelography

4 mSv

16 months

25X increase

Chest:

Computed Tomography (CT)-Chest

8 mSv

3 years

50X increase

Pulmonary  CTA

12 mSv

4 years

75 X increase

Radiography-Chest – PA/Lateral

0.16 mSv

10 days

- - - - - - - - - - - - - - -

Face and neck:

Computed Tomography (CT)-Sinuses

 0.6 mSv

2 months

3.8X increase

Heart:

 Cardiac CT for Calcium Scoring

2 mSv

8 months

12.5X increase

 Coronary CTA

15.4 mSv
(6 – 36mSv)

5 years

94 – 225X increase

Men's Imaging:

Bone Densitometry (DEXA)

 0.01 mSv

1 day

Less radiation

Women's Imaging:

Bone Densitometry (DEXA)

0.01 mSv

1 day

Less radiation

Galactography

0.7 mSv

3 months

4.4X increase

Hysterosalpingography

1 mSv

4 months

6.25X increase

Mammography

0.7 mSv

3 months

4.4X increase

Children's imaging:

Voiding Cystourethrogram

5-10 yr. old:
1.6 mSv

6 months

10X increase

Infant: 0.8 mSv

3 months

8X increase

References:

  1. FDA Document “What Are the Radiation Risks from CT?” - 12/19/2007
  2. ACR Response to NEJM article on Radiation Risk - 12/12/2007
  3. Brenner, Hall, et al Computed Tomography - An Increasing Source of Radiation Exposure - N Engl J Med 2007;357:2277-84.
  4. Radiographics 2006;26:503-12.Semelka RC, Armao DM, Elias J Jr, Huda W. Imaging Strategies to Reduce the Risk of Radiation in CT studies, Including Selective Substitution with MRI. J Magn Reson Imaging 2007;25:900-9.
  5. J Trauma 2004;56:475-80. Maytal J, Krauss JM, Novak G, Nagelberg J, Patel M. The Role of Brain Computed Tomography in Evaluating Children with New Onset of Seizures in the Emergency Department.
  6. Headache 2000;40:629- 32. Lee CI, Haims AH, Monico EP, Brink JA, Forman HP. Diagnostic CT Scans: Assessment of Patient, Physician and Radiologist Awareness of Radiation Dose and Possible Risks.
  7. Radiology 2004;231:393-8. Radiation Risks and Pediatric Computed Tomography (CT): A Guide for Health Care Providers.
  8. Rockville, MD: National Cancer Institute. (Accessed November 5, 2007, at http://www.nci.nih.gov/cancertopics/causes/radiation-risks-pediatric-CT.)
  9. McCollough CH, Bruesewitz MR, Kofler JM Jr. CT Dose Reduction and Dose Management Tools: Overview of Available Options.
  10. Pediatr Radiol 2000;30:546-50. Renton J, Kincaid S, Ehrlich PF. Should Helical CT Scanning of the Thoracic Cavity Replace the Conventional Chest X-ray As a Primary Assessment Tool in Pediatric Trauma? An Efficacy and Cost Analysis.
  11. J Pediatr Surg 2003;38:793-7. Kaups KL, Davis JW, Parks SN. Routinely Repeated Computed Tomography After Blunt Head Trauma: Does It Benefit Patients?
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