NEWS RELEASE, 11/16/99
Radiation expert warns of danger from overuse of medical X-rays, claiming they're responsible for many cancer and heart disease deaths
By Robert Sanders, Public Affairs
BERKELEY-- A noted University of California, Berkeley, expert on the health effects of radiation has concluded that a large proportion of deaths today from cancer and heart disease are due in part to past exposure to medical radiation.
John W. Gofman, professor emeritus of molecular and cell biology at UC Berkeley, conducted an intensive analysis comparing death rates in each of the country's nine census divisions with the average number of physicians per 100,000 people in these divisions.
The analysis turned up a major surprise. While death rates from almost all causes went down with increasing physician density, death rates rose with physician density in two categories: cancer and ischemic heart disease, also known as coronary heart disease.
Gofman, who for decades has warned of the dangers of low-level radiation, concluded that the cause is medical X-rays, including fluoroscopy and computed tomography or CT scans. The analysis and conclusions are published this week in a 700-page monograph by the book division of the Committee for Nuclear Responsibility, Inc., a non-profit, public interest association Gofman founded in 1971.
"This is a serious public health problem," Gofman said. "We're talking about the two biggest causes of death in this country - cancer and heart disease - which together amount to 45 percent of all deaths. Medical X-rays are a major cause of these deaths."
Gofman does not discount the role of other factors in these diseases, including diet and smoking, but maintains that more than half the deaths from cancer and heart disease would not have occurred but for medical X-rays.
He also acknowledges the value of X-rays in diagnosis and to monitor medical treatment. Nevertheless, he urges physicians to be careful of unnecessarily high doses of X-rays, and to advise patients of the pros and cons of X-rays, much as they alert patients to the possible side effects of drugs.
"My findings are not going to cause patients to reject the obvious benefits of medical X-rays," Gofman said. "People are smart. Very soon, patients may insist on seeing some evidence that they will receive the lowest possible X-ray doses."
He also urges radiologists to reduce radiation doses delivered in standard procedures, and in his study lists examples of how some hospitals and doctors have done this.
"These findings point to a safe and painless way to achieve big reductions in mortality from our two biggest killers, cancer and coronary heart disease," he said. "Reduce X-ray dosages, since the benefits of an X-ray can be obtained at much lower levels.
"When X-ray doses for mammograms were reduced tenfold, women began receiving the benefits with only one-tenth the former risk of getting cancer," added Gofman, who in 1995 published a study that ascribed 75 percent of breast cancer cases to past exposure from medical radiation. "But for many, many other X-ray procedures, the effort to achieve a tenfold reduction in dosage has not been made yet."
The problem, he argues, is an almost casual use of X-rays in the past. Through the 1940s, X-ray dosages often were 50 to 100 times those used today. Even as recently as the 1960s, mammograms sometimes delivered more than 100 times today's maximum allowed radiation dose. X-rays also were widely used for procedures doctors now know were unnecessary, such as routine X-rays during pediatric well-baby exams.
Though radiation doses have declined in many medical procedures, a proliferation of new uses of diagnostic and interventional radiation threatens to keep cumulative doses high, and thereby contribute to a higher mortality from heart disease and cancer, he said. What makes the situation even more alarming is that few physicians monitor the cumulative doses their patients get.
"There is the assumption that, at these doses, radiation doesn't make a significant contribution," he said. "But X-rays are very potent mutagens, even at low doses. It's a disaster that people still believe the 'safe dose myth,' that low doses are harmless."
Gofman, 81, has had a distinguished career in several fields, ranging from nuclear physics and lipoprotein research - he was the first to show that high levels of low-density lipoproteins, or LDLs, were a risk factor for atherosclerosis - to the health effects of radiation.
He began his recent analysis by using a huge census database that lists cause of death per age group within the country's nine census divisions, covering the entire population from 1940 to 1990.
He wanted to compare the death rates with estimates of the amount of medical radiation received on average by the population, but no such data exists. He therefore used a surrogate statistic: the number of physicians per 100,000 population, amassed over the years by the American Medical Association. He reasoned that since physicians prescribe X-rays, the number prescribed should be roughly proportional to the number of doctors serving the population.
Using regression analysis, he found that age-adjusted death rates for all types of cancer combined, and for ischemic heart disease by itself, rose with the number of physicians per 100,000 population in the census divisions. Conversely, all other diseases, when lumped together, showed a drop in the death rate as physician density rose. This held true in all age ranges.
Gofman argues that the correlation implies that death rates for cancer and heart disease have gone up as the number of medical procedures requiring radiation has gone up. Specifically, the study concludes that over 50 percent of the death rate from cancer today, and over 60 percent of today's death rate from ischemic heart disease, are induced by X-rays in combination with other factors.
"Prior to 1940, no medical exam was considered complete without X-ray procedures, generally including fluoroscopy where the X-ray beam stays on," he said. "In fact, X-ray exposure began even in the womb for many people who are now age 30 and over, because until 1970, about one birth in every 14 was preceded by pelvic X-rays of the mother shortly before delivery, to measure the birth canal."
He discounts other explanations for the correlation, such as urbanization, differences in autopsy rates, different rates of reporting cancer deaths, and the possibility that chemotherapy for cancer could have caused some of the ischemic heart disease.
Though it is not surprising that cancer rates go up with the number of medical X-rays, Gofman was surprised to find a similar situation with ischemic heart disease, even though he was aware of studies that suggest atherosclerotic plaques in the arteries can be stimulated by chemical mutagens.
"It has been known for decades that high doses of radiation injure or kill the heart and blood vessels," Gofman said. "This study is about low and moderate doses accumulated over time. Each dose, no matter how low, produces mutations, so by the time you're 50, all of these events have added to the mutation load in your cells."
Fluoroscopies in particular are a major source of radiation today, he said, because the beam stays on during the procedure, such as threading a catheter or endoscope. The total dose can easily be reduced, he said, by using the fluoroscope only periodically, not continually.
"This makes good sense for doctors and their patients," he said. "We must reduce the amount of radiation patients get, and measure it to make sure we're right."
The study was funded by numerous small gifts from individuals and private foundations.
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