On November 8, 2012, Environmental Health Perspectives, a monthly journal supported by National Institute of Environmental Health Sciences, National Institutes of Health, U.S. Department of Health and Human Services, published a report titled Radiation and the Risk of Chronic Lymphocytic and Other Leukemias among Chornobyl Cleanup Workers.
The report details the final results of a study conducted during the period from 2006-2012 and includes the names of twenty authors. It was funded in part by the National Cancer Institute, the US Department of Energy, the Nuclear Regulatory Commission and the French Institute for Radiological Protection and Nuclear Safety. The study objective was to estimate relative risks of chronic lymphocytic leukemia (CLL) and non-chronic lymphocytic leukemia (non-CLL) from protracted exposures to low-dose ionizing radiation.
The authors studied a population of 110,645 people who had been involved in efforts to clean up contaminated areas after the 1986 Chernobyl accident. The exposures were all received sometime during the period from 1986-1990.
Out of that large population, 162 (0.146%) were diagnosed with leukemia between 1986-2006. Of the 162, radiation dose estimates were not available for 25 people, leaving a group of 137. Out of the 137, 20 people were interviewed within 2 years after they started chemotherapy for their disease. That group demonstrated a significantly different dose-response from other cohorts so the people conducting the study decided to exclude them from the study results, leaving 117 cases of leukemia (both CLL and non-CLL) in the group to be studied.
Through a variety of statistical methods, the study authors determined that approximately 19 cases of leukemia (16% of the remain 117 cases, but just 0.017% of the initial group of 110,645) could be attributed to radiation doses received during the clean up effort.
Aside: Here is a quote from page 12 of the report that explains the “anomalous” dose-response of that group of 20. “However, preliminary analysis identified a significant (p=0.021) difference in the dose-response for 20 cases (6 non-CLL and 14 CLL) with direct in-person interviews <2 years from start of chemotherapy compared with other cases (ERR/Gy= -0.47, 95% CI: <-0.47, 1.02, p=0.244 for 20 cases vs.ERR/Gy=2.38, 95%CI: 0.49, 5.87, p=0.004 for the remaining 117 cases, Table 2 and Supplemental Material, Table S2). Due to this marked disparity, we limited our primary analyses to cases who were interviewed 2-15 years after start of chemotherapy, did not have chemotherapy, or for whom proxy interviews were used and their matched controls (85% of all cases and 83% of all controls)."
(Emphasis added. A negative number in ERR/Gy indicates a positive health response to increased radiation. Hmmm.) End Aside.
Using a technique called Realistic Analytical Dose Reconstruction with Uncertainty Estimation (RADRUE), which is a time-and-motion dose reconstruction method that uses questionnaires and field radioactivity measurements to model radiation exposure that was created specifically for this study and a related one, the study authors estimated doses to bone marrow of the people involved. According to page 11 of the report, the mean estimated bone marrow radiation dose for the studied population was 132.3 mGy (13.2 Rem). “Seventy-eight percent of study participants had doses below 100 mGy (10 Rem) and 87% below 200 mGy (20 Rem).”
There is an interesting contrast between my report summary above and the report abstract that Environmental Health Perspectives published.
Background: Risks of most types of leukemia from exposure to acute high doses of ionizing radiation are well known, but risks associated with protracted exposures, and associations between radiation and chronic lymphocytic leukemia (CLL) are not clear.
Objectives: To estimate relative risks of CLL and non-CLL from protracted exposures to low-dose ionizing radiation.
Methods: A nested case-control study was conducted in a cohort of 110,645 Ukrainian cleanup workers of the 1986 Chornobyl nuclear power plant accident. Cases of incident leukemia diagnosed in 1986-2006 were confirmed by a panel of expert hematologists/hematopathologists. Controls were matched to cases on place of residence and year of birth. Individual bone marrow radiation doses were estimated by the Realistic Analytical Dose Reconstruction with Uncertainty Estimation (RADRUE) method. A conditional logistic regression model was used to estimate excess relative risk of leukemia per gray (ERR/Gy) of radiation dose.
Results: A significant linear dose-response was found for all leukemia (137 cases, ERR/Gy (excess relative risk per gray)=1.26 (95% confidence interval 0.03, 3.58)). There were non-significant positive dose-responses for both CLL and non-CLL (ERR/Gy=0.76 and 1.87, respectively). In our primary analysis excluding 20 cases with direct in-person interviews
Conclusions: Exposure to low doses and low dose-rates of radiation from post-Chornobyl cleanup work was associated with a significant increase in risk of leukemia, which was statistically consistent with estimates for the Japanese atomic bomb survivors. Based on the primary analysis, we conclude that CLL and non-CLL are both radiosensitive.
NOTE: There is a section from the abstract of the actual paper that is missing from the abstract that is published on the abstract. On the web site, the “Results:” section ends with the word “interview.” In the paper itself, that section continues with the following:
…<2 years from start of chemotherapy with an anomalous finding of ERR/Gy= -0.47 (<-0.47, 1.02), the ERR/Gy for the remaining 117 cases was 2.38 (0.49, 5.87). For CLL the ERR/Gy was 2.58 (0.02, 8.43) and for non-CLL ERR/Gy was 2.21 (0.05, 7.61). Altogether, 16% of leukemia cases (15% of non-CLL, 18% of CLL) were attributed to radiation exposure.
I cannot explain why that section was left out, but it is possible that a the “less than” symbol interfered with a cut and paste. It is also possible that someone decided to obscure the fact that the final study cohort excluded a significant portion of the sample (15%) because their results did not match the stated objectives of the study.
A statistician considers a result to be “significant” as long as it is unlikely to have arisen simply by chance. Most people who are not statisticians or who have not been trained in statistical techniques use a rather different definition of the word, probably one or more of the following choices: “Having or expressing a meaning; meaningful” or “Having or likely to have a major effect; important” or “Fairly large in amount or quantity”.
Most radiation health specialists would not use the terms “low doses” or “low dose rate” to describe the exposures to a population with mean exposures of 13.23 Rem (132.3 mGy) received over a median period of just 35 days. (page 12)
The words that the study authors chose for their conclusions will be misinterpreted by many people. They will be repurposed by individuals and organizations with antinuclear or radiation protection agendas as “proof” that exposure at any level will inevitably result in an an increased risk of cancer.
People with antinuclear agendas or an already developed fear of radiation will not mention the fact that the increase is so slight as to be barely detectable. They will not mention that the small quantity of excess leukemia was found in a population that received far higher doses than anyone is expected to receive from even the worst postulated accident from a light water reactor designed to internationally accepted standards. They will fail to mention the fact that there was a hint found in the study that indicated that the leukemia, even if initiated by a radiation dose, was treatable. (Recall that the people conducting the study excluded a group of 20 people whose dose response indicated a ERR/Gy of -0.47 with a confidence interval that ranged from <-0.47 to 1.02 because that group had been treated with chemotherapy.)
I hope you are now armed with enough information to understand and to challenge the people who are going to try to misuse the results of this credible statistical modeling effort, which was conducted by nearly two dozen credentialed researchers during six years of intensive effort.
There is a back story explaining why I wrote this post.
At about 10:00 am on November 8, a friend posted the following note on an email list populated by people who are interested in using social media tools and techniques to share accurate information about nuclear energy.
I can’t find the report itself in downloadable form (a little bit of help?), but if this article is anywhere near accurate in its data reported, this could be some serious fuel for the no-safe-level crowd.
There was a little flurry of discussion about the article from others who participate on that email list. One of the more tuned-in members noted that the reliably antinuclear NIRS (Nuclear Information Resource Service) had tweeted about the release of the study within minutes after its announcement.
At 6:00 pm on November 8, 2012, I received the following email from an Atomic Insights reader:
First, thank-you for all of the work you do in maintaining this website, and providing an oasis of reason amidst an almost overwhelming sea of alarm regarding nuclear power and radiation.
I live in Japan, am a mechanical / electrical engineer by training, and have learned more than I ever expected to about nuclear power over the past year and a half.
I write in to bring your attention to a paper published on Nov. 8 in “Environmental Health Perspectives”, entitled “Radiation and the Risk of Chronic Lymphocytic and Other Leukemias among Chornobyl Cleanup Workers”.
A link to the main journal site is here:
The paper itself is here:
I am curious whether one or more of the people who comment on your articles might examine this paper and provide insight into the conclusions and/or methods and analysis used in the paper.
The analysis of bio/medical data is just enough beyond my skill set that I would like to hear from others before the common FUD folk start proclaiming the validity of the linear dose rate theory all the way down to zero.
I decided to do what many journalists who work on tighter deadlines than I do will not do – I read the press release, the abstract and the full report. Once again, my rather eclectic educational mix that includes deep study of English literature, statistics, radiation biology, politics, business and nuclear technology has provided a unique lens for reading between the lines.
Value for Value Request
If you found this summary to be useful, maybe you could say thanks by making a contribution on my Movember page. During the month of November I’m growing a new mustache (what my Aussie friends might call a ‘Mo’) to replace the one I shaved off on October 31 when I began my participation in Movember. The participants are working to raise funds that will help treat forms of cancer that are not leukemia – specifically prostate and testicular cancer.