Study: Low Doses Of Radiation Linked To Leukemia

[Uni of California etc] Low doses from Chornobyl cleanup work was associated with a significant increase in leukemia (Fukushima Diary, Nov 10, 2012):

University of California and other educational institutions published the report to prove low level of exposure causes leukemia.

The details are like below.

Title

Radiation and the Risk of Chronic Lymphocytic and Other Leukemias among Chornobyl Cleanup Workers

URL

http://ehp.niehs.nih.gov/2012/11/1204996/

Researchers

Lydia B. Zablotska,1 Dimitry Bazyka,2 Jay H. Lubin,3 Nataliya Gudzenko,2 Mark P. Little,3 Maureen Hatch,3 Stuart Finch,4 Irina Dyagil,2 Robert F. Reiss,5 Vadim V. Chumak,2 Andre Bouville,3 Vladimir Drozdovitch,3 Victor P. Kryuchkov,6 Ivan Golovanov,6 Elena Bakhanova,2 Nataliya Babkina,2 Tatiana Lubarets,2 Volodymyr Bebeshko,2 Anatoly Romanenko,2 Kiyohiko Mabuchi3
1Department of Epidemiology and Biostatistics, School of Medicine, University of California, San Francisco, San Francisco, California, USA, 2National Research Center for Radiation Medicine, Kyiv, Ukraine, 3Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, USA, 4Robert Wood Johnson Medical School, Camden, New Jersey, USA, 5Departments of Pathology and Medicine, College of Physicians and Surgeons, Columbia University, New York, New York, USA, 6Burnasyan Federal Medical Biophysical Centre, Moscow, Russia

Published

November 8, 2012

Conclusion

The present study provided evidence of increased risk of leukemia associated with chronic
protracted exposure to low doses of ionizing radiation. The finding from our primary analysis of
similar radiogenic risks both for CLL and non-CLL was based on a well-defined population-

based cohort, rigorous case ascertainment and expert hematological review, coupled with wellcharacterized radiation dose estimates. In our cohort of cleanup workers from 1986 through
2006, about 16 % (19 cases) of all leukemia were attributed to radiation exposure, with similar
estimates for non-CLL (15%) and CLL (18%). CLL is the most common type of leukemia in
this cleanup worker population and, as they age, CLL cases will rapidly increase, raising
concerns for medical consequences. The radiogenic risk for CLL also has important public
health implications in other populations as it is the most prevalent type of leukemia in Western
populations, with approximately 16,000 cases estimated to be diagnosed in the U.S. in 2012
(Howlader et al. 2012). Further investigations are needed to develop a better understanding of
the association between radiation and CLL.

Result

The age at diagnosis of 137 cases ranged from 25 to 78 years (median=56) and the corresponding
age for 863 controls ranged from 25 to 79 years (median=55). Mean estimated bone marrow
radiation doses and standard deviations (SD) for cases and controls were 132.3 mGy (342.6) and
81.8 mGy (193.7), respectively (Table 1). Seventy-eight percent of study participants had bone

marrow doses below 100 mGy and 87% below 200 mGy. Cases and controls did not differ
significantly by urban vs. rural residential status at the time of interview, age at first radiation
exposure in the 30-km Chornobyl zone, or education; however, more cases than controls were
proxy-interviewed (p<0.001) (Table 1). Cases and controls did not differ significantly by
calendar year of first cleanup mission, type of work or total number of missions, or by selfreported smoking, alcohol consumption, medical or diagnostic radiation exposures, or
occupational exposures to chemicals or radiation before and after the Chornobyl accident (results
not shown). Thirty-eight percent of cleanup workers were in the 30-km zone around the
Chornobyl nuclear power plant for over two months (median time in the zone for all workers=35
days, range 1-1,711 days, similar for cases and controls p Wilcoxon=0.729).
For all leukemias, we found a significant positive association with continuous radiation
dose with an estimated ERR/Gy=1.26 (95% CI: 0.03, 3.58, p=0.041) (Table 2). 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).
Relative risks increased with increasing radiation dose for all leukemia (Figure 1). Tests
for quadratic, exponential or power deviations from the linear dose-response shown in Figure 1
were not significant (p=0.927, p=0.917, p=0.267, respectively). The dose-responses increased

significantly for both non-CLL (ERR/Gy = 2.21, 95% CI: 0.05, 7.61, p=0.039) and CLL
(ERR/Gy = 2.58, 95% CI: 0.02, 8.43, p=0.047) subtypes, with tests for interaction consistent
with homogeneity (p=0.888) (Table 2).
There was no significant difference in ERR/Gy estimates by proxy or direct interviews
(p=0.420), calendar period of diagnosis (p=0.141) or type of work performed in the 30-km
Chornobyl zone (p=0.711) (Table 2). Although also not significant, ERR/Gy estimates tended to
decrease with increasing time (years) from first radiation exposure in the Chornobyl zone and to
increase with increasing age at first exposure (p=0.162, p=0.249, respectively) (Table 2). The
proportion of proxy vs. direct interviews decreased over time (60.0%, 73.9%, 55.6%, and 54.2%
for cases diagnosed in 1986-1989, 1990-1994, 1995-2000, and 2001-2006, respectively).
We estimated that approximately 16 percent of all leukemia cases in our Chornobyl
cleanup worker population over a period of 20 years of follow-up (PAR=16.4%, 95% CI: 3.9,
32.6) were attributable to radiation exposure from the Chornobyl accident. The majority of the
PAR arose from dose groups of <200 mGy in which there were large numbers of cleanup
workers (Figure 2). Proportions of non-CLL and CLL cases attributable to radiation were
similar, with a PAR of 15.4% (95% CI: 0.4, 38.5) and 17.5% (95% CI: 0.2, 41.0), respectively.
For completeness, we evaluated modifications of the ERR/Gy presented in Table 2
using all case and control data (Supplemental Material, Table S2). In general, results using the
full dataset were consistent with the primary analysis. However, the ERR/Gy for CLL (0.76,
95% CI: <-0.38, 3.84, p=0.352) was lower than the estimated ERR/Gy for CLL from our primary
analysis excluding 14 CLL cases (2.58, 95% CI: 0.02, 8.43, p=0.047). In the analysis using the
full dataset, as in the primary analysis, the ERRs were not significantly different between CLL
and non-CLL outcomes (p=0.536).

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