Carcinogenesis and adaptive effects of low doses of chronic internal ionizing radiation: child leukemia in Belarus after Chernobyl accident

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ionizing radiation and carcinogenesis

So far, the question of whether acute leukemia (AL) incidence has increased as a resuit of Chemobyl is of great scientific and public health interest. It is known that the link between childhood AL (ChAL) and radiation is well documented (1-3). However, our previous data (4) showed no increase in the incidence rate (IR) of ChAL in Belarus (general group, age 0-14) 5 years (1986-1991) after Chemobyl ac­cident. This data were confirmed in Scandinavian countries (5,6), broader European studies (ECLIS) (7), in Germany(8), case-control investigation in Russia and Bela­rus (9).However, Petridou et al.(10) reported that infants exposed in utero to ionizing radiation from Chemobyl accident had 2.6 times the IR of AL compared to unexposed children. No significant difference in IR was found among children aged 1-4 years old. In Belarus, too, a trend of increased infant leukaemia rates is observed among the cohort of children who were most liable to be exposed to radiation from Chemobyl in utero (11). Noshchenko et al. (12,13) and Busby (14) showed a significant association between radiation exposure and AL risk, increasing sharply at low doses (0,02 mSv) and falling at high doses (2,0 mSV). We present results of an ecological epidemiology study in Belams looking at temporal trends in IR of ChAL through age-cohort-period analyses in 1979-2008. It is comprised of 2324 children (0-14 years old) newly diagnosed leukaemia cases between 01.0.1979 and 01.01.2009. Numbers of cases were tabulated by year, age at diagnosis and periods of observation (preaccident, 1979-1985 (+1.01-30.04.1986) and postaccident, 1.07.1986-31.12.2008) (table 1).

Table 1

Acute leukemia following the Chemobyl accident in Belarus 1986-2008

Age group

Period of time
1979-1985 (1) 1986-1992 (2) 1993-1999 (3) 2000-2008 (4)
N IR+SE N IR+SE N IR+SE N IR+SE
0-1 49 4.33±0.62 67 6,36+0,51 16 2,29+0.57 8 1,06+0.35
1-4 277 6.41+0.39 304 6.64+0.38 208 6,25+0.43 203 6,28+0.50
5-9 211 4.08±0.28 218 3,95+0.26 154 2,86+0.23 135 3,03+0.26
10-14 118 2.30±0.21 119 2,36+0.21 119 2,09+0.19 118 2.17+0.21
0-14 655 4.23±0.17 708 4,35+0.16 497 3,28+0.15 464 3,23+0.15

Since 1979 the occurrence of leukaemia has been documented accurately through the Registry of Blood diseases of the Research Institute of Hematology (1988) and Belarusian Cancer Registry. The patients had to be inhabitants of Be­larus and were grouped by age at diagnosis. AL diagnostic accuracy was confirmed by the intemational experts (15). Rates were standardized directly to the Standard world population.

Doses of the whole body irradiation of children as a resuit of the Chemobyl ac­cident (in mSv as equivalent doses ) were in 1986-1992, 1993-1999, 2000-2008 accordingly for 0-1: 1,95; 0,23; 0,15; for 1-4: 6,14: 1,03; 0,54; for 5-9: 10,32; 5,59; 1,44; for 10-14: 10,4; 11,34; 3,02. Dose reconstruction was based on available country-specific radiation monitoring data and estimates of exposure levels to populations (16). A slight tendency to increasing of ChAL incidence observed soon after the Chemobyl accident in general group (0-14 year old) in 1986-1992 — 4,23 vs 4,35. The RR is 1.095 (90% CI — 0,946 to 1.131, statistically not significant, X=0,383, p=0,268). However, the IR of ChAL of the children exposed in utero or in early infancy (0-1 age old, mean individual equivalent dose on the bone marrow about 13 mSv — from 0,04 — 186 mSv) was increased signiflcantly. As we can see (tabi. 1), before the Chemobyl accident the inbom AL met in 49 infants (among them — 34 (69,4%) ALL, 9 (18,4%) AML and 6 (12,2%) AUL; in 1986-1992 — 67 infants had AL (52 ALL (77,6%), 10 AML (14,9%) and 5 AUL (7,5%). (RR: 1,47,CI 95% 1,02-2,12, p=0,04). In 1993-1999 was revealed diminish of incidence to 16 cases (9 ALL (56,3%), 4 AML (25%), 3 — AUL(18,7%); in 2000-2008 numbers of AL were 11 cases for 9 years. It was noticed the increasing of AML in the infants. IR did not change in 1-4 year old children after 22 years in postchemobyl period. IR ChAL in children 5-9 and 10-14 years old was stable in 1986-1992, but it is decreasing significantlyin 1993-1999.

These changes gave in general group (0-14) the decrease of IR ChAL in postchernobyl period (1993-2008). IR AL in cohort 15-19, 20-24, 25-29 years old before Chemobyl accident (non exposed group) did not differ from IR the same age groups (exposed one) in postchemobyl period.

Thus, the carcinogenic effects of an ionizing radiation exposure in low doses may be restricted to children exposed in utero or in early infancy (0-12 months). The carcinogenesic effect of low doses of the ionizing radiation exposure was absent in cohort 1-4, 10-14 and 15-29 years old, exposed during 22 years to whole-body <0,2 mSv — >3 mSv.

It was revealed also the developing of adaptive response to the low and very low (<0,02 mSv) dose during intemal chronic ionizing radiation exposure. As a resuit, the IR of ChAL became less then it was before accident and after 15 year follow-up. Such conclusions were made also by Busby (14).

References:

  1. Preston D.L. et al. [l] Res. l37(Suppl.), S 68-97 (1994).
  2. Bithell J.F. et al. Br.J.Cancer, 31,271-287 (1975).
  3. Doli R. et al. Br.J.Radiol.,70, 130-139(1997).
  4. Ivanov EP et al. (1993) Nature 365: 702.
  5. Auvinen A et al. (1994) BMJ 309: 151-154.
  6. Hjalmars U, et al. (1994) BMJ 309: 154-157.
  7. Parkin DM et al. (1966) BJ Cancer 73: 1006-1012.
  8. Michaelis J et al. (1997) Nature 387: 246.
  9. Davis S. et al. (2006) Intern.J. Epid. (2006): 35: 386-396.
  10. Gibson, B. et al. Lancet 1988,2,630.
  11. Ivanov EP.et al. (1998) Radiat Environ Biophys: 37 :53-55.
  12. Petridou E et al. (1996) Natura 382: 352-353.
  13. Noshchenko AG et al. (2002) Int.J.Cancer 99: 609-618.
  14. Noshchenko AG et al. (2009) Int.J. Cancer.
  15. L.McCarthy et al. (2004) Leuk.Res.:28:1273-1280.
  16. Cardis et al. (2006) Int.J.Cancer: 119, 1224-1235.

 

Authors: V. Ivanov, T. Terehovich, E. Ivanov
Source: Медико-социальная экология личности: состояние и перспективы: Материалы IX Междунар. конф., 1-2 апр. 2011 г., Минск / редкол.: В. А. Прокашева (отв. ред.) [и др.]. – Минск:  Изд. центр БГУ, 2011. – 434 с. Ст. 88-90.

Канцерогенез и адаптивные эффекты малых доз хронического внутреннего ионизирующего излучения: детская лейкемия в Беларуси после чернобыльской аварии

Авторы: В. Иванов, Т. Терехович, Е. Иванов

Установлен гормезисный эффект малых доз чернобыльской ионизирующей радиации при хроническом внутреннем облучении радионуклидами.