Radiation-II: Low level-What We Know and Can't Know
New truths in science often begin as heresy, advance to orthodoxy, and end as superstition.
If you don't read the newspaper you are uninformed; if you do read the newspaper you are misinformed.
At the turn of the 20th Century the hazards of radiation* were poorly understood, especially before and after World War I when radium was considered a cure-all and radium patent medicines could be purchased at the corner drugstore. Eben Byers, a U.S.amateur golf champion, wealthy socialite and industrialist faithfully drank 2-ounce bottles of Radithor every day. He died in 1932 of aplastic anemia, multiple brain abscesses, and jaw decay. Marie Curie died of aplastic anemia two years later. Evidence of the deadly effects of radioactivity accumulated over the years as the tragedies of the radium dial watch painters unfolded in New Jersey. Marie Curie's daughter Irene-another Nobel Laureate, succumbed to leukemia in the 1950s. early radiologists lost fingers, and like many researchers and patients exposed to large doses of radiation, suffered life-shortening as well as succumbed to various cancers. After the explosions of the atomic bombs over Hiroshima and Nagasaki in 1945, the dangers of high-level ionizing radiation became well known, and the principal task of experts was to determine the safe level of radiation exposure.
Much of the past 7 decades has witnessed a continuing battle over whether there is indeed a "threshold" level below which no harm is done. To put the matter in perspective, everyone agrees there is ample evidence of carcinogenicity and mutagen effects at very high and medium radiation dose levels-above 7-10 rem (70-100mSv). But at lower levels of exposure the evidence of this effect is extremely obscure and virtually impossible to document.
There is little question that high doses of ionizing radiation, >100 mSv (10 rem), given acutely or during a prolonged period, produce serious harm, including, but not exclusively, cancer. "At lower doses, however, the situation is less clear. It seems unlikely that we will be able to directly estimate risks at significantly lower doses than these because of the practical limits of epidemiology." Yet the same authors go on to state, "...that risks cannot be directly estimated at doses below, say, 5 mSv (500 mrem) does not imply any conclusion as to whether risks actually exist at these lower doses." 500 mrem is only-one-tenth the yearly dose of 5000 mrem (5 rem) allowed radiation workers by Government. (CFR 20).
A large study recently showed that overall mortality in the UK's 175,000 radiation workers is lower than that in the general population. This "healthy worker effect" explains that workers usually exhibit lower death rates than the general population, because- the severely ill and disabled are ordinarily excluded from employment. Yet the researches used other mathematical tricks to conclude that yes, radiation workers did have a higher mortality than the normal population.
Can We Know How Low is Safe?
One method used to increase the accuracy of epidemiologic studies of radiation-induced cancer. is to select populations, such as the subgroups of Japanese who were exposed to varying, but large amounts of radiation, and then attempt to infer the effects of low level by backwards extrapolation.
Unfortunately, there is no general agreement on any method of performing similar extrapolations. It is virtually impossible to prove statistically that the effects of low level radiation are reduced in frequency from those of a high exposure level. First and possibly foremost, there is the epidemiological bÍte noir of various biases:(selection, exclusion, information, reporting, recall, time, and even publicity bias). This makes any study of large populations a statistical nightmare. Last but not least, even assuming the biases can be "modeled" somehow, the population required would be in the millions.
About 23% of all American died of cancer in 2006 For each additional. At a dose of 1 mSv or 100 mrem an increase in death rate of less than 0.01% has been assumed by many researchers. All such estimates must be regarded as scientifically suspect, because the available data does not support what is clearly a mirage. This means that the carcinogenicity of amounts of radiation exposure routinely encountered by the population, is vastly exceed by the known carcinogenicity of many of the chemical compounds found in our own environment. This was convincingly shown by a study of the incidence of several different cancers and of heart disease in 43 urban areas. (Hickey et al, Health Physics, 1981)
My position remains that fear of exposure to ionizing radiation should never be invoked as a reason for omitting any indicated radiological procedure. A corollary of this is: you needn't have the dental hygienist cover you with a lead apron when she X-rays your uppers or lowers.
Rosalyn Yalow, nuclear medicine pioneer and Nobel Laureate has done an outstanding job in refocusing the attention of the scientific community on the fallacious reasoning affecting government policy. As long ago as 1981 she reminded us that a Government report to the Congress concluded, after 80,000 papers and $2 billion spent, that "there is as yet no way to determine precisely the cancer risks of low level ionizing radiation and that it is unlikely that this question will be resolved soon."
Dr. Yalow's "resolved soon" has turned into three more decades and more billions of dollars down the drain in a futile search for a "safe level" of radiation exposure, looking for a definitive answer to an undecidable question. For starters Google the search terms. "dangers of radiation" and you come up with 1.64 million hits. Could this continuing hemorrhage of research money be better spent? Undoubtedly. But it just goes to prove that decades of studies in this, as in many other intellectual archipelagos, represent the last refuge of the scientifically destitute.
* Radiation refers to ionizing radiation, electromagnetic waves (or particles) that are energetic enough to detach electrons from atoms or molecules.
Martin F. Sturman, MD, FACP
Copyright 2010, Mathemedics, Inc.
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