But sadly, many women are still hesitant to have regular mammography examinations, often because they fear that X-rays from the mammograms will increase their chances of cancer. Doing their own risk assessment, they conclude the risk from "late detection" is less than that from radiation. And who is to blame them, in light of the commonly accepted dictum that all radiation is dangerous and cumulatively so? Besides, it costs time and money to have a mammogram - at least worrying about cancer is cheap.
"So," you say, " they should just consult a professional and ask about the dose they will receive from the mammogram and make the decision on that basis." Not as simple as that may sound. In researching this chapter I called four local mammography clinics with what I thought was a pretty simple question: "What is the dose of radiation received by a woman in the process of having a mammogram?" I had seen a figure before, but it seemed high to me.
I spoke with two mammography technicians and one nurse who relayed messages from their radiologists. The unanimous answer: "We don't know." One of them, however, was kind enough to put me in touch with a local health physicist, who said the dose was "negligible" - but, even better, offered to lend me some of his reference books. In one, I was able to find the range of exposures to a "gland" (their quotation marks) at a dept of 3 cm to be 0.04 to 0.49 cGy (40 to 490 mrem), which was consistent with the 0.15 cGy figure I had found earlier and was trying to confirm.
But the information I had was perplexing, as it mentioned the dose as 150 mrem per breast. It was much like the confusion I had when learning that radon gave an exposure of 24,000 mrem/year to the bronchial epithelium (which, of course, you now know is the windpipe). The borrowed volumes were quite illuminating, I found there is an official weighting factor that, when multiplied by the local dose gives the effective dose equivalent. And what does this tell you? It tells you the increase in your chances of contracting cancer if the Linear No-Threshold theory were true!
Using a weighting factor of 0.15 for each breast, a 150 mrem per breast exposure would be an equivalent "whole body" exposure totaling 45 mrem (0.045 cSv). [Exposure of the U.S. Population from Diagnostic Medical Radiation, NCRP Report #100, National Council on Radiation Protection and Measurements, Bethesda, Md.]
The figure - in my opinion - means nothing, but if we pretend it is accurate we can use it as a starting point for a "conventional" analysis.
Published in the New England Journal of Medicine in 1989, an investigation by A.B. Miller and associates charted the doses received by 31,710 women who were irradiated in the course of repeated fluoroscopic examinations between 1930 and 1952. [Miller, A.B., et al. Mortality from breast cancer after irradiation during fluoroscopic examination in patients being treated for tuberculosis. New England Journal of Medicine, 321, 1285, 1989.]
In this Canadian study, one group - in Nova Scotia - was fluoroscoped facing the X-ray source. This results in a dose to the breast approximately twenty-five times that when faced away. The women facing the source had a significant increase in cancer risk - it tripled for each 100 cGy (100,000 mrad) of radiation absorbed.
The balance of the study was for all other provinces, with the results presented in Figure 28. Before going on, please remember that a normal annual U.S. background dose is 0.3 cGy, with the first data point on the graph at 5 cGy - about thirteen times this amount. The minimum mortality rate is at a value fifty times the annual background dose or the equivalent (using their figures) of 100 mammography exams.
On the basis of this evidence - which is almost certainly conservative, since the dose rate for fluoroscopy is much higher and, therefore, considered more traumatic to the breasts than present mammography techniques - women should have four or five mammograms per year.
Does that sound strange? That's nothing compared with the most unusual aspect of the study, namely its conclusion: The authors completely ignored the most statistically significant data points in the entire investigation, namely the 34% reduction in relative risk at 15 cGy and the 15% reduction at 24 cGy. Myron Pollycove, M.D., remarked regarding this omission:
"The decreased RR [risk rate] of breast cancer produced by low dose, low level radiation were rejected a priori by the choice of mathematical models that extrapolate the dose-risk relation from high dose exposures to low dose exposures."
[We met Dr. Pollycover back in Chapter 2. But since he is such an important player in the LNT controversy, allow me to remind you that he is professor emeritus in Laboratory Medicine and Radiology at the University of California at San Francisco, head of Nuclear Medicine at San Francisco General Hospital, as well as a visiting medical fellow on the Nuclear Regulatory Commission.]
To most of us that simply means the researchers, for whatever reason, chose to "spike" all results that indicated hormesis. Why? Probably because they were not even considering bio-positive data; they were looking for harmful effects... period. Pollycove continues:
"Nine hundred excess deaths from breast cancer are predicted theoretically from the exposure of one million women to 0.15 Gy. However, the quantified low dose data predicts with better than 99% confidence limits that instead of causing 900 deaths, a dose of 0.15 Gy would prevent 10,000 deaths in these million women."
Pardon me, but do you understand what this man - who has possibly the most impressive credentials in this entire debate - is saying? He is proclaiming that there is unmistakable evidence of hormesis in this study, which, if acted upon, might be developed into an effective weapon against breast cancer in millions of women, thousands of whom will die needlessly because of a theory that was never intended to apply to low-level radiation! It is a pity, a shame, a disgrace that the current ingrained reliance by regulators on the Linear No-Threshold hypothesis makes even a consideration of studying the hormesis phenomen extremely difficult, if not impossible.