by Robert Sanders
A large percentage of the breast cancers seen today were caused by medical X-rays prescribed decades ago before the long-term effects of radiation were recognized, says a Berkeley expert on radiation effects.
John Gofman, professor emeritus of molecular and cell biology, estimates that at least two-thirds--and probably 75 percent or more--of the 182,000 cases of breast cancer diagnosed each year are due to X-rays received up to 60 years ago for a variety of medical conditions.
Breast cancer today is the most common cancer in women, with one in eight women expected to develop breast cancer in their lifetimes. While often curable in its early stages, it remains the number one cause of cancer death in women aged 20 to 54 years.
"The good news is that a great deal of breast cancer is preventable," Gofman says. "You don't have to buy my estimate of 75 percent--what's important is that my study alerts the medical profession and the public that ionizing radiation may be an important or the dominant cause of breast cancer."
Gofman reached his conclusions after spending more than six months delving into the medical literature on past use of X-rays, concentrating on articles published between 1920 and the 1970s. What he discovered was an era when overzealous doctors X-rayed patients for a broad range of benign ailments, not suspecting it might have consequences decades later.
Most of the uses have fallen from favor, such as routine X-rays during pediatric well-baby exams, X-rays to diagnose and treat enlarged thymus glands, standard X-ray exams of pregnant women to assess whether they can safely deliver vaginally and X-rays to monitor the course of lung collapse therapy for tuberculosis.
But through the 1940s X-rays were commonly used for these and other reasons, with dosages often 50 to 100 times those used today. Even as recently as the 1960s mammograms to detect breast cancer sometimes delivered more than 100 times the maximum allowed radiation dose today.
As a result, adults and many children received repeated doses of ionizing radiation that today would be considered hazardous.
"Though medical X-rays now deliver much lower doses, doctors and patients should not be complacent," Gofman says. Many medical procedures today are monitored with fluoroscopes that deliver small X-ray doses but are left on for a long period of time. Children and adults in intensive care units can receive numerous X-rays over the course of their treatment and even accident victims are X-rayed repeatedly to provide evidence for insurance.
Each X-ray delivers a cumulative dose of ionizing radiation that over a lifetime could increase breast cancer and other cancers, he warns.
"I'm not saying don't do X-rays," Gofman says. "But doctors should think about it as they do a procedure and ask, do I really need to leave that fluoroscope on?"
Gofman published the results of his research this month in a new book "Preventing Breast Cancer: The Story of a Major, Proven, Preventable Cause of this Disease" (Committee for Nuclear Responsibility, Inc., 1995).
Gofman has argued for years that even low levels of radiation can cause cancer, a view that conflicts with the more widely held hypothesis that there is a certain threshold below which radiation is safe.
The conclusions of his new study, however, come from an analysis of moderate to high radiation exposure, he points out. Some routine X-ray treatments 50 years ago delivered up to 400 rads of radiation. By
contrast, today's chest X-rays deliver about 15 thousandths of one rad, while the average yearly dose from natural sources of radiation is one tenth of a rad.
"For the future it's a big issue whether low doses count," Gofman says. "I think one of the most important things medicine can do to prevent breast cancer is work out X-ray procedures that deliver even lower doses."