Health effects of radiation exposure

1. Health effects of radiation exposure Tilman A Ruff Nossal Institute for Global Health, University of Melbourne Advisor: Australian Red Cross, AusAID/UNICEF Consultant: GSK Biologicals, Novartis Vaccines Medical Association for Prevention of War International Campaign to Abolish Nuclear Weapons Hunter’s Hill Inquiry, Sydney 4 July 2008

2. Overview • Overview of radiation • Sources of environmental radiation • Health effects of radiation

3. Radiation Basics Radiation – Energy in transit: • electromagnetic waves (gamma-γ or x-ray), or • high speed particles ( alpha-α, beta-β, neutron-η, etc.) Ionizing Radiation – Radiation with sufficient energy to remove electrons during interaction with an atom, causing it to become charged or ionized • Can be produced by spontaneous radioactive decay or by accelerating charged particles across an electric potential (eg x-rays)

4. Introduction • What is ‘radiation’? • Electromagnetic energy • Spectrum

5. Ionizing vs Non-ionizing • Ionizing radiation has high energy and displaces electrons from their orbits creating charged atoms (ions)/molecules • Creates DNA damage • Outright cell death • Bystander effect • Genomic instability • Non-ionizing radiation creates heat due to low energy eg infrared, MRI

6. Radiation types

7. Ionizing Radiation Sources • Average global dose: 2.4 mSv

8. Ionizing Radiation Sources

9. Multiple exposure pathways • External - often gamma • Most easily measured • Direct contact – skin • Internal • Inhale – gas, dust, aerosol • Ingest • Food – many radioisotopes bioconcentrated • Water • Environmental source esp young children • Wounds

10. Radiation Basics Radioactivity – 1 Becquerel (Bq)= 1 radioactive disintegration per sec Absrbed dose – 1 Gray (Gy) = 1 joule of energy deposited per kilogram Equivalent dose (biological effect) – Sievert (Sv) the unit of absorbed dose equivalent. The energy absorbed by the body based on the damaging effect for the type of radiation. Sv =Gray x Quality Factor

11. Radiation Quantities and Units • Biological equivalent dose: Sievert (Sv) = joules per kilogram • Relates to the amount of radiation harm in biological tissues • Beta, gamma, and x-ray Sv = Gy • Particle weightings (electrons = 1; neutrons = 5; alpha = 20) • Biological effective dose: Sievert (Sv) = equivalent dose weighted for susceptibility to harm of different tissues

12. U-238 radioactive decay

13. tissue injury: alpha-particle track … lung cells

14. Radon • Produced from radium in decay chain of uranium • Escapes into air – short lived decay products emit alpha particles – stick to dust, inhaled, deposit in lung – high but localised radiation • Second most important cause lung cancer

15. Radon • Average outdoor levels: 5-15 Bq/m3 • Global indoor average: 39 Bq/m3 • Action levels – generally 200-400 Bq/m3 (Australia 200) • Risk of lung cancer increases by 16% per 100 Bq/m3 increase in radon • Relationship linear with no threshold • Risk synergistic with smoking • Some (weak) evidence of increased effect at low dose rate

16. Radon risk per 1000 of lung cancer by age 75 y WHO Factsheet 291 June 2005

17. Cell Sensitivity • Cells most affected: • Rapidly dividing cells: • small intestines, bone marrow, hair, fetus

18. Varying tissue sensitivities

19. Health Effects of Radiation

20. Ionising radiation • Capacity to damage core genetic blueprint - DNA → cancer → other health effects → genetic damage • Lethal dose can have equivalent energy to heat in a cup of coffee • Many different isotopes • Behave differently biologically

21. Biological Effects of Radiaton • Deterministic effects (>100mSv) • Threshold • Increased dose = increased damage • Stochastic (probabilistic) effects (no safe threshold) • Increased dose = increased probability of damage but not severity

22. Delayed Somatic Effects • 1. Cancer: solid tumors • Increased risk • Latency period: 10+ y • 2. Cancer: leukemia • Increased risk • Latency period: 5+ y • 3. Degenerative effects (LSS, not sure at low doses) • Life shortening (not sure) • Heart disease, stroke; digestive, respiratory, hemopoietic systems

23. Cancer Risks • Normal cancer risk (Australia): • About 1:2 men get cancer by age 85 • About 1:3 women get cancer by age 85 • Normal mortality: • 29% of Australians die primarily from cancer • 49.3 % die primarily or as a consequence of cancer Cancer in Australia: an overview 2006, AIHW

24. Cancer Risks • Linear, no threshold • Increased risk of cancer from 1 mSv of radiation: • Solid tumor cancer risk about 1 in 10,000 • Leukemia risk about 1 in 100,000 • Increased risk of cancer mortality about half those : • Solid cancer deaths: about 1 in 20,000 • BEIR VII 2005

25. Cancer risks vary • Infancy 3-4x increased risk cf 20-50y • Female infants 2x risk of male infants • Female risk of cancer is 37.5% greater than males • 50% greater risk of solid tumours • Less risk leukaemia • BEIR VII 2005

26. Fetal radiation risk • There are radiation-related risksthroughout pregnancy that are related to the stage of pregnancy and absorbed dose • Radiation risks are most significant during organogenesis and in the early fetal period, somewhat less in 2nd trimester, and least in 3rd trimester Most risk Less Least

27. Leukaemia and cancer • The relative risk may be as high as 1.4 (40% increase over normal incidence) due to a fetal dose of 10 mSv • For an individual exposed in utero to 10 mSv, the absolute risk of cancer at ages 0-15 is about 1 excess cancer death per 1,700

28. Medical Radiation Exposure

29. CT Scanners

30. CT Scanners

31. Nuclear industry workers 1 • 15 country retrospective cohort study of cancer mortality auspiced by IARC • Largest such study ever conducted • Workers involved in fuel enrichment or reprocessing, reactors, weapons or isotope production (excl uranium mining) • 407,391 workers (90% male): • employed ≥ 1 y • monitored for external photon (X and gamma) radiation • > 90% whole body dose from external photons rather than neutrons or internal exposures • Total FU 5.2 million person y

32. Nuclear industry workers 2 • Doses to colon used for all and solid cancer, active bone marrow for leukemia analyses, lagged by 2 y for leukemia and 10 y for other cancers • Doses: • Average 19.4 mSv • 90% < 50 mSv • < 0.1% > 500 mSv • Total deaths 6516 from cancer other than leukemia, 196 from leukemia excl CLL

33. Nuclear industry workers 4 • Mortality from all cancers except leukemia – central estimate 2-3 times higher than linear extrapolation from atomic bomb survivors • Current recommended 5 y occup dose limit of 100 mSv → 9.7% (1.4 - 19.7%) increase in cancer excl leukemia • For leukemia excl CLL 100mSv → 19% (<0 - 84.7%) increase Cardis E, et al. BMJ 2005 (29 June 2005) BMJ,doi:10.1136/bmj.38499.599861.EO

35. ‘Routine’ radiation releases • First large meta-analysis of data on childhood leukaemia and nuclear facilities • International peer-reviewed journal • Multiple sites, different populations, different time periods, collected differently are difficult; findings more likely to be significant • No major sources of bias identified • Countries with poorer environmental standards eg Russia, China and developing countries are excluded, so likely best case scenario • Effects robust to different types of analyses

36. ‘Routine’ radiation releases • Point estimates are all above 1 • A number of important findings are statistically significant eg all of the results for childhood leukaemia incidence • Association of young age and closeness to a nuclear facility with higher risk are biologically plausible, suggest dose-response effect • Heightened sensitivity of children to radiation, and leukaemia as most radiation sensitive cancer with shortest latent period support biological plausibility • funded by the US DOE

37. German Childhood Cancer Registry data 1980 – 2003, <5y • Matched case-control study • 593 leukemia cases • Odds ratio for leukemia 2.19 (lower 95% CI 1.51) for residence within 5 km of nuclear power plant

39. 1592 cases, 4735 controls • Odds ratio 1.47 (lower 95% CI 1.16) for inner 5 km zone

40. Thank you!