The Risks of Undiagnosed Cancer vs the Theoretical Risks of Radiation Exposure

The Hippocratic Oath underscores that harm to patients can result either from acts of commission or omission. Decisions about the use of diagnostic imaging are now under great scrutiny. Medicine is attempting to find a balance between the need to assess the patient’s clinical status, and the potential risks of radiation exposure in diagnostic imaging. The Image Gently and Image Wisely campaigns reaffirm the long-held ALARA (“as low as reasonably achievable”) principles of radiation protection.[1] The dilemma facing physicians is which will do more harm to the patient: an act of commission, ie, performing diagnostic imaging, or an act of omission, ie, deferring to clinical assessment alone.

Goske and colleagues, in their review on page 232 of this issue,[2] indicate that the potential harm of radiation in medical imaging has been extrapolated largely from data on atomic bomb survivors. Such data clearly demonstrate the risk of radiation exposure at doses greater than 100 mSv. With exposures of less than 100 mSv, however, it is not statistically possible to identify an increased risk for cancer compared with the normal incidence of cancer in the exposed populations.[3,4] Most important, exposures from intermittent medical imaging with low-energy x-rays and gamma rays to limited anatomic regions cannot be directly compared to a whole-body exposure resulting from an atomic bomb or nuclear accident involving high-energy gamma rays, neutrons, and charged particles.

The Science Committee of the International Organization for Medical Physics [IOMP] published a policy statement which asserted that predictions of induced cancers and cancer deaths in a population of patients exposed to < 100 mSv of ionizing radiation during medical imaging procedures is highly speculative, due to multiple uncertainties that include generalization of risk across different populations, as well as dosimetric and methodological issues.[5] The IOMP, along with other internationally recognized scientific committees, concluded that “there is no reason to deter from any justified medical examination involving exposure to ionizing radiation.”[5]

Nonetheless, the expanded use of medical imaging in the United States has renewed the debate about its potential benefits and harm. In the early 1980s, the total per capita radiation dose was 3.6 mSv, with only 0.54 coming from medical imaging and the remainder from background radiation.[2] In 2006, the total per capita radiation dose was 6.2 mSv, with medical radiation accounting for 3 mSv of the total. However, while the exposure nearly doubled, it is still far less than the 100 mSv level below which there is statistical uncertainty about the health effects of radiation. The debate over radiation risk has raged with particular virulence with regard to mammography-yet multiple studies have shown that the risk of radiation-induced breast cancer from yearly mammograms is small compared with the expected mortality reduction from such screening.[6]

While the use of medical imaging has increased over the past 3 decades, there has been no associated increase in cancer deaths; in fact, the age-adjusted death rates from cancer have either declined dramatically or have remained stable.[6] Advances in cancer diagnostic imaging and therapy resulted in a 12.1% decline in US cancer deaths and significant increases in overall life expectancy between 1950 and 2010, with the most significant decline in cancer deaths achieved after 1980, coincident with increases in diagnostic imaging.[7-9] This length of follow-up also is sufficient to account for the 5- to 20-year latency period for development of radiation-induced cancers.

The declining rates of cancer mortality are a testament to the value of the diagnostic and therapeutic innovations of the past 3 decades, including innovations in medical imaging. However, the definition of “harm” is now being reconsidered, with the theoretical and acknowledged low risk of diagnostic studies thought to be as harmful as the potential of death from undiagnosed disease-but it must be remembered that harm can result as easily from an act of omission as from an act of commission.

References:

1. Code of Federal Regulations, Title 10, Section 20.1003 [10 CFR 20.1003]. ALARA. December 11, 2013. Available from: http://www.nrc.gov/reading-rm/basic-ref/glossary/alara.html. Accessed February 4, 2014.

2. Goske MJ, Frush DP, Brink JA, et al. Curbing potential radiation-induced cancer risks in oncologic imaging: perspectives from the ‘Image Gently’ and ‘Image Wisely’ campaigns. Oncology (Williston Park). 2014;28:232-43.

3. Hendee WR, O’Connor MK. Radiation risks of medical imaging: separating fact from fantasy. Radiology. 2012;264:312-21.

4. Pierce DA, Preston DL. Radiation-related cancer risks at low doses among atomic bomb survivors. Radiat Res. 2000;154:178-86.

5. Pradhan AS; on behalf of the IOMP Science Committee. On the risk to low doses [< 100 mSv] of ionizing radiation during medical imaging procedures-IOMP statement. J Med Phys. 2013;38:57-8.

6. Yaffe MJ, Mainprize JG. Risk of radiation-induced breast cancer from mammographic screening. Radiology. 2011;258:98-105.

7. American Cancer Society. Cancer facts & figures, 2013. Atlanta: American Cancer Society; 2013.

8. Howlader N, Noone AM, Krapcho M, et al (eds). US mortality trends, 1950-2010. SEER cancer statistics review, 1975-2010; posted to the SEER web site April 2013. National Cancer Institute; Bethesda, MD. Available from: http://seer.cancer.gov/csr/1975_2010/; Accessed February 4, 2014.

9. Murphy SL, Xu J, Kochanek KD. Deaths: final data for 2010. National Vital Statistics Reports. Vol 61, No 4. US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Health Statistics. May 8, 2013.

10. Arias E. United States life tables, 2009. National Vital Statistics Reports. Vol 62, No 7. US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Health Statistics. January 6, 2014.