Radiology and nuclear medicine subject matter experts have published an article in the January 2017 issue of The Journal of Nuclear Medicine that provides numerous reasons why people should never worry about properly controlled radiation doses used in medical imaging. The doses used are many times lower than the lowest dose at which harm might begin in the form of an association with slightly high cancer risk.
That statement is true even when referring to studies on the survivors of the atomic bomb blasts at Hiroshima and Nagasaki with continuing follow-up for effects of acute exposures that happened in August 1945.
Using language aimed at the professional audience that subscribes to The Journal of Nuclear Medicine, Siegel, Sacks and Pennington make the case that it is wrong and dangerous to stubbornly cling to a “no safe dose” hypothesis that was contradicted by experimental evidence available before the assertion was invented and promoted.
Brief history of LNT (aka “no safe dose”) basis for radiation protection limits
It’s possible that Hermann Muller, the “no safe dose” inventor, did not recognize what his own data showed about the measurable effects. Even if Muller’s interpretation was not purposefully false, his bold confidence and stubborn repetition — starting in 1946 and lasting through his death in 1967 — of the claim that a “no-harm threshold was non-existent” wasn’t justified by the series of experiments that he performed. The lowest dose Muller tested was 4 Gy (4,000 mGy).
At least some of the bureaucrats that have been responsible for developing radiation protection regulations during period since 1945 apparently took Muller’s assertion literally, even if they were unaware of the history behind the incorrect statement that “all radiation causes cancer”.
Without any evidence of harm, selected officials agreed to eliminate the concept of “permissible dose” that had governed the first 50 years of radiation exposure control and to gradually implement ever lower limits. Under current rules promulgated by the Environmental Protection Agency (EPA) and enforced by the Nuclear Regulatory Commission (NRC) and various responsible state regulatory bodies, areas are considered to be unacceptably contaminated with radiation if the “all pathways” annual dose is just 0.15 mGy.
Though radiation protection regimes differ around the world, all of them have been strongly influenced by the U.S. regulatory paradigm.
Officials in Japan are striving to achieve a post Fukushima clean-up in which projected annual doses in as many areas as possible are below 1 mGy. They consider anything above 20 mGy/yr to be a “no go zone” even though studies of radiation workers in the US haven’t shown any harm during careers in which their annual dose limit is 50 mGy. Remember, Muller didn’t study anything below 4,000 mGy.
Ostensibly, radiation protection standard setters were charged with using scientific knowledge to protect public health and safety. The published works of many of them indicate that they honestly believe that is what they are doing by enforcing low limits on radiation. Many radiation protection professionals also accept the philosophy of “As Low As Reasonably Achievable (ALARA)” that is a close cousin of the Linear, No-Threshold (LNT) assumption (aka “no safe dose”).
Some people interpret ALARA to mean that no expenditure is unreasonable as long as it leads to a reduction in radiation doses. They believe they are “protecting the public” when they recommend that people leave their homes, possessions and communities behind to avoid doses that are five times lower than the lowest dose with evidence of an association with a tiny increase in cancer rates. ALARA advocates overlook, however, the fact that many people believe that they need to add additional margins of safety to what the government tells them is an adequately safe limit. Seeking zero dose is not only impossible, recommended actions to “optimize” dose often ignore the risks associated with avoiding radiation.
Applying “no safe dose” to medical imaging
Siegel, Sacks and Pennington have many things to say about the substantial illogic [“non sequitur of non-trivial proportion”] of applying ALARA principles to medical imaging. They name the key proponents of the fear-inducing campaigns.
Brenner et al. [Brenner D, Elliston CD, Hall EJ, Berdon WE. Estimated risks of radiation-
induced fatal cancer from pediatric CT. AJR. 2001;176:289–296] perhaps started the frenzy over CT dose and cancer risk. On the basis of an LNTH calculation involving unsupported parameters with significant uncertainties, they projected that approximately 500 children under the age of 15 y would die of cancer attributable to CT radiation.
The irresponsibility of this projection was underscored by International Commission on Radiological Protection Publication 103 and others stressing that the low-dose risk uncertainties of the LNTH show it should not be used to calculate hypothetical cancers from small radiation doses received by large populations. According to Lauriston Taylor [Taylor LS. Some nonscientific influences on radiation protection standards and practice: the 1980 Sievert lecture. Health Phys. 1980;39:851–874.], this type of calculation is based on a literal application of the LNTH, treating it as fact even though there is no statistical or other verification of this calculation. Such claims, he said, are “deeply immoral uses of our scientific knowledge.”
They also point out the damage that is caused in the name of being “prudent” in the face of officially accepted uncertainty.
Many grant the absence of low-dose harm yet nevertheless advocate lower imaging dose as a prudent approach; but this conflates actual prudence, restricting medical procedures to those clinically indicated, with the prejudice-based false prudence of limiting clinically indicated imaging doses.
This unjustified, radiophobia-centered approach falsely vilifies beneficial imaging without confirmatory data and entails extremely harmful conse- quences. The declaration that the LNTH provides “known” cancer risks due to imaging must stop. The use of the LNTH and the advocacy for ALARA dosing by various groups (e.g., Image Wisely and Image Gently) are misguided and not science- or evidence- based.
These groups serve only to frighten rather than to educate, further enhancing the probability of negative outcomes; we therefore recommend that the imaging community come together to decide whether the activities of such groups should be terminated.
(paragraph marks added)
Many Atomic Insights readers are comfortable reading articles packed with words like “iatrogenic”, “non sequitur” [I had to look that one up, even though I had a vague understanding of its meaning], “artifice”, “excessive relative risk”, “Poisson regression”, “chromosome aberrations” and “interventional cardiologists”. If you are one of those people, please invest the time in reading the full article.
The authors would appreciate people who take a few minutes to provide comments to the editor of the JNM. (Instructions for letters to the editor of JNM can be found in the left hand column of page 3A of its Information for Authors document.)