Breast cancer detection tests and the risk of ionizing radiation

A little over a week ago, an article in the New York Times reported on a recent study evaluating the increased exposure to potentially harmful radiation posed by two new FDA approved nuclear-based imaging examinations. We asked Thomas Kolb, M.D., assistant clinical professor of radiology at Columbia University College of Physicians and Surgeons, and a member of the WVFC Medical Advisory Board, to offer his comments.  —Ed.

One of the most common worries by women who consider being screened with mammograms is the effect of X-rays (ionizing radiation) on their bodies. We have all been educated that radiation can cause mutations in cells which can lead to cancer. How, then, can mammograms (which use X-rays to depict the breast) be beneficial? The answer lies in weighing the benefits versus the risks.

The risks of mammograms–and for that matter any test that uses ionizing radiation, including CT scans–have been exhaustively studied and reported in the Biologic Effects of Ionizing Radiation (BEIR) VII report. This 700-page document is produced by the National Research Council and is widely accepted in many nations as a primary source of radiation risk estimates and protective regulations.

BEIR VII shows 82 percent of human exposure of radiation is from natural sources, while 10 percent is due to medical X-rays (compare with 4 percent from consumer products). While medical X-rays make up only a small fraction of human exposure to low-level radiation, the BEIR VII calculates the age-dependent risk of radiation-induced cancers and deaths caused by breast imaging modalities that use ionizing radiation.

This can then be compared with the decrease in mortality (in other words, lives saved) by annual mammographic screening. The benefit of screening with mammograms significantly outweighs the risks.

Two new breast imaging tests, both approved by the FDA — at left,Breast Specific Gamma Imaging (BSGI) , and and at right, Positron Emission Mammography (PEM) — are performed after the intravenous injection of a radionuclide which exposes many organs in the body to ionizing radiation.

While these tests have been incompletely evaluated in the literature, they show promise of having equal or higher sensitivity for breast cancer when compared with MRI. However, a research paper by Dr R. Edward Hendrick in the September issue of Radiology, “Radiation Doses and Cancer Risks from Breast Imaging Studies,” reports that the radiation dose of both these tests was markedly higher than that of the benchmark mammogram.

While digital mammography has an average lifetime risk of inducing 1.3 fatal breast cancers per 100,000 women aged 40 at exposure, a single B.S.G.I. exam was estimated to involve a lifetime risk 20 to 30 times greater in women aged 40.

The lifetime risk of a single P.E.M. was 23 times greater. Based on his findings, Dr. Hendrick concluded, “The results indicate that BSGI and PEM are not good candidate procedures for breast cancer screening because of the associated higher risks for cancer induction per study compared with the risks associated with existing modalities such as mammography, breast ultrasound and breast MR.”

The take-home point is that while tests may be FDA-approved, they may not be advantageous to the patient. The-benefit-to-risk ratio must be much more completely evaluated and established as beneficial before these newer tests can be utilized for breast cancer screening.

While discussion of radiation risk is necessary, it is crucial to understand that neither breast ultrasound or MRI uses ionizing radiation.

They have not been shown to induce cancer. In my own practice, this week two high-risk patients who were scheduled for Breast MRI canceled because of radiation fears. This is unwarranted and demonstrates the need for more complete patient education.

Breast MRI involves no radiation exposure.

Thomas Kolb, M.D. has been on the faculty of numerous medical educational meetings, and he has lectured throughout the U.S. and internationally on the topic of breast cancer detection and diagnosis, including at the New York Academy of Sciences and the Radiological Society of North America. In 1998, Dr. Kolb published the first contemporary study detailing the use of screening breast ultrasound to detect cancers, and in 2002 his publication describing the performance characteristics of mammography, clinical breast examination and ultrasound was awarded the Scientific Paper of the year by the American Medical Association. Dr. Kolb is currently a principal investigator of the North American Digital Breast Tomosynthesis project, which is analyzing a novel mammographic technology that acquires multiplanar images of the breasts.

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