Radiation Expert
Warns of Danger From Overuse of Medical X-Rays
Research Suggests They're Responsible for Many Cancer, Heart Disease Deaths
By Robert
Sanders, Public Affairs
Posted December 1, 1999
Too much medical radiation exposure has led to a large proportion of today's deaths from cancer and heart disease, according to research by a Berkeley expert on the health effects of radiation.
John Gofman, professor emeritus of molecular and cell biology, 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 CT scans.
"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 to 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."
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."
December 1, 1999 -
January 11, 2000 (Volume 28, Number 16)
Copyright 1999, The Regents of the University of
California.
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