Experts publish dueling messages on low radiation doses
DOI: 10.1063/PT.5.8124
Late June saw worldwide media publicity for two scientific articles engaging an old health-physics question: Is there a threshold dose below which ionizing radiation is harmless? Maybe it’s scientifically useful that the coinciding articles’ conclusions directly oppose each other. After all, scientists routinely confront complexity. But what about public perceptions if the enthusiastic publicity registers outside the technorealm, attracting attention to the stark contrast in the two messages from science?
One of the articles, an analysis of past studies, moves far in the direction of saying yes, there is indeed a threshold dose below which ionizing radiation is harmless. On 30 June, a EurekAlert press release appeared about it from the science news distribution service of the American Association for the Advancement of Science, which publishes Science magazine. Here’s the key passage:
“Although radiation is known to cause cancer at high doses and high dose rates, no data have ever unequivocally demonstrated the induction of cancer following exposure to low doses and dose rates,” Dr. [James] Welsh and co-author Jeffry Siegel, PhD, write.
Studies that have found a cancer link to medical imaging typically employ a model called “linear no-threshold” (LNT). In LNT, the well-established cancer-causing effects of high doses of radiation are simply extrapolated downward in a straight line to low doses. The LNT model assumes there is no safe dose of radiation, no matter how small.
But although LNT is used by regulators around the world, the model “is of questionable validity, utility and applicability for estimation of cancer risks,” Drs. Welsh and Siegel write.
Contrary to the LNT model, there is compelling evidence that the human body has evolved the ability to repair damage from low-dose radiation.
The publicized paper ‘s title begins, “Does imaging technology cause cancer?” Notably, though, the subhead goes past “questionable” and “contrary” in the direction of affirming that yes, there’s a threshold. The subhead says, “Debunking the linear no-threshold model of radiation carcinogenesis.” Excerpts from the paper’s abstract show a certain media-aware combativeness in the analysis, complete with disdain-conveying quotation marks in the phrase “this reported ‘scientific’ literature” and, at the end, the accusation “overly simplistic model":
In the past several years, there has been a great deal of attention from the popular media focusing on the alleged carcinogenicity of low-dose radiation exposures received by patients undergoing medical imaging. . . . The media has based its reporting on the plethora of articles published in the scientific literature that claim that there is “no safe dose” of ionizing radiation, while essentially ignoring all the literature demonstrating the opposite point of view. But this reported “scientific” literature in turn bases its estimates of cancer induction on the linear no-threshold hypothesis of radiation carcinogenesis. . . . [T]he risk:benefit ratio models used to calculate the hazards of radiological imaging studies may be grossly inaccurate if the linear no-threshold hypothesis is wrong. Here, we review the myriad inadequacies of the linear no-threshold model and cast doubt on the various studies based on this overly simplistic model.
As of 1 July, these conclusions and views were being reported by the UK’s Daily Mail and elsewhere.
Meanwhile the Lancet Haematology article “Ionising radiation and risk of death from leukaemia and lymphoma in radiation-monitored workers (INWORKS): an international cohort study” moves far in the direction of saying no, there is no threshold dose below which ionizing radiation is harmless. “This study,” the paper emphasizes, “provides strong evidence of positive associations between protracted low-dose radiation exposure and leukaemia.” In this case the worldwide publicity takes the form of the 30 June Nature news article “Researchers pin down risks of low-dose radiation: Large study of nuclear workers shows that even tiny doses slightly boost risk of leukaemia.” It reports that the scientific article “scuppers the popular idea that there might be a threshold dose below which radiation is harmless.” That is, it supports what the other paper claims to “debunk": the LNT model.
Whether or not any biophysicist, oncologist, or health physicist expects convergence and consensus on LNT any time soon, these two coinciding, opposing, well-publicized studies call to mind the science-can’t-make-up-its-mind phenomenon gently satirized by the comedian Woody Allen in the 1973 movie Sleeper. A 28-second online clip shows two scientists of the future marveling at the ignorance of the past, when no one recognized the nutritional benefits of hot fudge, deep fat, steak, and cream pies.
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Steven T. Corneliussen, a media analyst for the American Institute of Physics, monitors three national newspapers, the weeklies Nature and Science, and occasionally other publications. He has published op-eds in the Washington Post and other newspapers, has written for NASA’s history program, and is a science writer at a particle-accelerator laboratory.