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Letters to the Editor |
Department of Radiology, Wesley Southernex Imaging, Wesley Hospital, 40 Chasely Street, Brisbane, Queensland 4066, Australia
e-mail: chris_allen{at}health.qld.gov.au
As a result of a recent policy review regarding computed tomographic (CT) pulmonary angiography in young women, we have identified what we believe is an important error concerning a much-quoted breast cancer risk figure. Hopper et al (1) state that "with use of data obtained in A-bomb [atomic bomb] survivors, Land et al predict that the delivery of 1 rad (0.01 Gy) of radiation to a breast of a woman younger than 35 years increases her lifetime risk of breast cancer by 13.6%." However, the original study by Land et al (2) examined women who were exposed at less than 20 years of age and developed breast cancer at less than 35 years of age. Land et al proposed that there may be a susceptible subgroup of women who are more likely to develop radiation-associated breast cancer and that this subgroup is identified only by the fact that these women developed breast cancer. Taking this into account, the 13.6% figure quoted in the article by Hopper et al (1) and cited in numerous subsequent publications, including those by Remy-Jardin and Remy (3), Nickoloff and Alderson (4), and Rehani (5), has been inappropriately and incorrectly referenced.
Law and Faulkner (6) have given age-stratified lifetime risks of breast cancer; with their figures, the lifetime risk of breast cancer for a 30-year-old woman exposed to 1 rad (0.01 Gy) of radiation is one in 5000, which equates to a lifetime increase in relative risk of 0.2% (assuming a one in 10 lifetime risk). The data are less certain for younger patients, but certainly a doubling of this risk for 20-year-olds (one in 2500) and a further doubling for 10-year-olds (or one in 1250) would be a reasonable worst-case assumption. A typical chest CT examination delivers 2.5 rad (0.025 Gy), which would give an increased lifetime risk of breast cancer in 10-year-olds of one in 500. This fits with the report by Dr Brenner and colleagues (7) that approximately one in 1000 pediatric CT examinations will cause a fatal cancer.
Doctors need to be aware of the risks of radiation when ordering x-ray–based examinations, and it is essential that the most accurate information possible is available when making risk-benefit decisions. It may be that many clinicians underestimate the risk of radiation, but equally a massive overestimation of the risk as quoted by Hopper et al (1) needs to be corrected to allow clinicians to make well-informed investigative decisions.
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Center for Radiological Research, Columbia University Medical Center, 630 West 168th Street, New York, NY 10032
e-mail: djb3{at}columbia.edu
Drs Allen and Demetriades are absolutely correct that the risks of low-dose radiation-induced breast cancer have often been considerably mischaracterized—some being unrealistically high, as Drs Allen and Demetriades point out, but others being unrealistically low (1).
Happily, our ability to quantify low-dose breast cancer risks has recently been considerably enhanced by the publication of the 2005 National Academy of Sciences Biological Effects of Ionizing Radiation (BEIR) VII Report (2). This report includes updated estimates of lifetime attributable risk for cancer of the breast (and other sites) as a function of age at exposure. Previous reports had included only age-dependent breast cancer mortality data (3) or incidence data for a single age at exposure (4).
Thus, for example, the new lifetime breast cancer risk estimates (2) for a 0.25 cGy dose to the breast, typical of the mean glandular dose from screening mammography (5), are about 11 per 105 women exposed at age 20 years, decreasing to about 6 per 105 for age 30 years and to about 3.5 per 105 for age 40 years. Corresponding estimated breast cancer mortality risks are about 2.5 per 105 for women exposed at age 20 years, decreasing to about 1.5 per 105 for age 30 years and about 1 per 105 for age 40 years.
The really major advantage of the new BEIR VII breast cancer risk estimates is that they are derived from an absolute risk model that is based on both Japanese atomic bomb data and three U.S. cohorts of radiation-exposed women (2,6). This eliminates the major uncertainty in transporting risks from a Japanese population where baseline breast cancer risks are very low to Western populations where baseline risks are much higher. As such, while the new risk estimates are not greatly different from earlier values (3,4), the uncertainty in these new breast cancer risk estimates (estimated to be ±36%) is much smaller than in previous assessments.
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  A. M. Strashun A Reduced Role of V/Q Scintigraphy in the Diagnosis of Acute Pulmonary Embolism J. Nucl. Med., September 1, 2007; 48(9): 1405 - 1407. [Full Text] [PDF]
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 A. Scarsbrook, K. Bradley, F. Gleeson, A. M. Groves, S. J. Yates, T. Win, I. Kayani, J. Bomanji, and P. J. Ell Perfusion Scintigraphy Still has Important Role in Evaluation of Majority of Pregnant Patients with Suspicion of Pulmonary Embolism Radiology, August 1, 2007; 244(2): 623 - 625. [Full Text] [PDF]
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 A. F. Scarsbrook and F. V. Gleeson Investigating suspected pulmonary embolism in pregnancy BMJ, February 24, 2007; 334(7590): 418 - 419. [Full Text] [PDF]
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