Risks of Medical Radiation
Kenneth Strubler, D.A.B.R., D.A.B.M.P.
Director, Medical Physics & RSO
More is known about the biological effects of radiation than any other hazard to humans. It is the most studied, best understood and perhaps most wisely used agent in our society. And yet, it still occupies a special place in our closet of anxieties. Much of the concern has been in response to the association with nuclear weapons, the revelations of government experiments on patients, and the published concerns about radon and, now, the threat of radioterrorism. The public hears conflicting pronouncements from the scientific community. Sensational reports in the press foster distortions. The facts never quite catch up with the half-truths or fiction. So it is natural that many questions and concerns still persist.
Life is a risky business. All human activities entail some risk. In general, new risks are usually associated with improved standards of living. We drive automobiles, use electricity, fly in airplanes, heat our home with volatile fuels, bungee jump, play baseball, undergo surgeries, take chemicals of all types - aspirin, vitamins, hormones among them. All represent a step forward from life in prior generations, but each one carries with it a small but finite risk of injury. Radiation falls into this category.
All of us are exposed to radiation in our daily lives. There is a natural, background level of radiation consisting of cosmic rays, terrestrial radiation from rocks, soils and building materials, and even from radioactive substances that are naturally found in the human body. In addition, the inhalation of naturally occurring radon gas has received much attention and contributes to our 'natural' radiation exposure. Unlike most technical advances, radiation has been present before we knew anything about it. Low-level background radiation has not had any significant impact on mankind's development. It is, therefore, used as a yardstick with which to compare artificially produced man-made radiation. That is, exposure of the public from man-made radiation from industry and medicine that is similar to natural background levels can be considered to pose little or no risk.
The concern over radiation exposure of man arises from the observation that effects for HIGH doses and HIGH dose rates are usually detrimental, and the necessary assumption that these effects may arise to some degree at very much lower doses such as those encountered in a medical environment. An important perspective should also be understood that virtually anything in high doses or taken to excess is usually harmful - vitamins & minerals, food additives, pesticides, alcohol, pollutants, salt, candy, aspirin, drugs & chemicals of any kind; fists, knives, bullets, bombs, swimming with sharks.
There is no way to determine precisely the risks of low-level radiation. To date, no proven body of evidence has established an increase in either human disease or other harmful effects as a consequence of radiation dose rates and cumulative exposures comparable to those of natural background or even at doses 10-fold higher! We may be uncertain of the exact risk but we know that the risk is very small, particularly when compared to other risks we accept in our lives whether by choice or imposed on us by others.
To be more specific, the average natural background radiation to the U.S. population is about 300 millirems per year. The millirem (one thousandth of a rem) is a unit to describe the amount of radiation. While this unit has been replaced with a newer one, it is still suitable for discussion and illustration. Background radiation is much higher (2-3 times) in the Colorado plateau area. In other parts of the world it is as much as five times higher than in this country. Many epidemiological studies have shown that there is NO increased incidence of ill health in those populations living in very high background radiation compared to people of similar cultures living in adjacent, low background regions.
Are x-rays safe? How much radiation am I getting? These are questions occasionally asked by patients. The radiation exposure from medical x-ray examinations varies enormously depending on the study. At the low exposure end are extremity exposures and chest x-rays. CT (or CAT scans) and fluoroscopic examinations comprise those procedures giving, at times, much higher doses. It is convenient to correlate medical exposure to the natural background radiation that we all receive. For example, a posterior chest x-ray (10-20 millirems) is equivalent to about 10 days of background radiation, while a head & neck exam (100-300 millirems) is equal to a few weeks, the pelvis a few months and a dental bitewing x-ray about 4 days.
It has been calculated that the risk from 10 millirems of radiation is comparable, in theory, to the risk of driving your car about 30 miles or from smoking 1.4 cigarettes or from drinking 1/2 liter of wine or from living 2 days in New York City. The risk estimate from low levels of radiation is purely hypothetical and is likely to be much less than stated. That is, the risk from 10-1000 millirems of diagnostic radiation may well be zero.
However, there are specific circumstances for special attention. Because the developing embryo and fetus are more sensitive to radiation, we do ask all procreative women for the potential for pregnancy. This is done to be prudent and conservative before exposing this small but very important population to unnecessary radiation. In general, if an x-ray exposure will benefit the mother, then the benefits will exceed the risks for the baby as well.
For more detailed information about radiation used in medicine, consult an expert such as a Health Physicist, Medical Physicist ,or Radiation Safety Officer.
