Biological consequences of ionizing radiation

1. Biological consequences of ionizing radiation BNEN 2012-2013 Intro William D’haeseleer

2. Prologue (1) • From Chemical context (Cfr P. Pôlet) To illustrate this, I wish to tell the following anecdote. A British scientist had written a study about risks. His study had the correct inclination: he said that it is not the product, but the dose that makes the poison. The thesis of the British scientist was that you could blame every product if you only use the “appropriate” arguments. He wanted to test this and towards that purpose, he interviewed 123 at random in the London underground stations. His question was:

3. Prologue (2) • From Chemical context (Cfr P. Pôlet)

4. Prologue (3) • From Chemical context (Cfr P. Pôlet) You certainly have understood this: indeed, he was talking about … . Well, about 5% said no, 19% said that they did not know, but 76% (>3/4) agreed to ban ! Unbelievable, but true. It shows the serious challenge the chemical industry is up to to improve its image and to overcome this sort of phobia.

5. Prologue (3) • From Chemical context (Cfr P. Pôlet) You certainly have understood this: indeed, he was talking about … . Well, about 5% said no, 19% said that they did not know, but 76% (>3/4) agreed to ban water ! Unbelievable, but true. It shows the serious challenge the chemical industry is up to to improve its image and to overcome this sort of phobia.

6. Back to Radioactivity & Ionizing Radiation

7. Ionizing particles Recall • Directly ionizing particles alpha (He-4++) & beta (e-/e+) • Indirectly ionizing particles Gamma or X rays/photons & neutrons

8. Impact ionizing particles • How dangerous is radiation? Cfr. B.L. Cohen:

9. Health impact ionized radiation…eh? «When one of these particles or rays goes crashing through some material, it collides violently with atoms or molecules along the way…. In the delicately balanced economy of the cell, this sudden disruption can be disastrous. The individual cell may die; it may recover. But if it does recover… after the passage of weeks, months or years, it may begin to proliferate wildly in the uncontrolled growth we call cancer.» Ref: S. Novic, “The careless atom”, Dell, NY, 1969

10. Impact ionizing particles • B.L. Cohen continued:

11. Impact ionizing particles • B.L. Cohen still continued:

12. Impact ionizing particles Indeed, due to natural radiation: number of e/i pairs in person 70 kg ~ 109 = 1 billion per second x 60 years(taking into account weight evolution 020y) ~ 1 à 2 1018 ionizations over one’s whole life = one billion times one billion ! How come we don’t all die like flies???

13. External radiation / Contamination Fundamental difference between External (ir)radiation and Contamination Radioactive source outside body Radioactive source inside body

14. External radiation / Contamination • External (ir)radiation

15. External radiation / Contamination • External (ir)radiation - depends on type of radiation αβγ n - shielding * natural: air / water / soil * engineered: concrete, Pb - distance - irradiation time

16. External radiation / Contamination • Contamination Especially for α & β sources ! When inside the body, not possible to shield α can cause considerable damage β relatively dangerous Contamination of the skin: “whipe” / “scrub” clean

17. External radiation / Contamination • Contamination Now also biological T1/2 time to remove half of radioisotope from body urine, stools, sweating, exhaling,…, vomiting,… Effective T1/2λeff= λph + λbio 1/Teff = 1/Tph + 1/Tbio Smallest T1/2dominates Teff

18. Special Characteristics • Note the passive nature of radio-isotopes • Do not have “legs”  do not migrate actively • Can only migrate passively  must be transported away by carrier (e.g., dissolved,…) • Because of ionizations • Ionizing radiation (as a rule) well measurable(compared to e.g., chemical / toxic substances)

19. Dose Concepts

20. Units & Radiation Concepts • Recall Activity [=] Bq Source characteristic # disintegrations/sec

21. Units & Radiation Concepts • Flux or Intensity or “exposure”[=] #/(sm2) Field characteristic # particles/(sm2)

22. Units & Radiation Concepts • Absorbed Dose [=] J/kg or Gy Receiver characteristic Energy/mass Joule/kg Old unit rad; 1 Gy = 100 rad

23. Units & Radiation Concepts • Dose Equivalent [=] Sv Receiver characteristic in man Energy/mass Weighted for distribution deposited energy & biological damage Old unit rem; 1 Sv = 100 rem

24. Units & Radiation Concepts • Dose Equivalent [=] Sv Receiver characteristic in man(for LL radiation) Q = 1 for X, gamma and Beta Q = 20 for alphas Q = 5 – 20 for neutrons (dependent upon energy) (Sometimes correction factor for dose rate or fractionation N)

25. Units & Radiation Concepts • Collective Dose Equivalent [=] man-Sv Receiver characteristic in men/womenfor populations (LL radiation) 1 Man-Sv = 1000 people at 1 mSv = 100 people at 10 mSv Only makes sense in linear relationship Dose & Effect Careful for very small Doses & very large populations  0 x ∞ = unstable

26. Biological effects • Physiology of man

27. Biological effects • Cell Biology

28. Biological effects • Possible biological consequences Ionizations … free radicals … upset chemical bonds … potential damage cell… perhaps biological damage

29. Biological effects • Interactions of radiation with cells: 4 stages Initial physical stadium Energy deposition & ionization E.g., H2O → H2O+ + e-

30. Biological effects • Interactions of radiation with cells: 4 stages Physico-chemical stadium Interaction ions with H2O  new products E.g., H2O+→ H+ + OH H2O + e- → H2O- H2O- → H + OH- Ions H2O- H2O+ H+ OH- Free radicals OH H

31. Biological effects • Interactions of radiation with cells: 4 stages Reaction products interact with organic molecules in the cell Chemical stadium (some seconds) Nuclear Energy 2011-2012 William D’haeseleer

32. Biological effects • Interactions of radiation with cells: 4 stages • Reaction products interact with organic molecules in the cell • Death of cell • Impairing cell division • Change (in nucleus of cell)  transferred to daughter cells Chemical stadium (some seconds) Biological stadium minutes - years Nuclear Energy 2011-2012 William D’haeseleer

33. Biological effects • Reference for more detail:

34. Biologic effects of radiation • Somatic effects (own-body related) a) Early effects due to acute high doses = “deterministic effects” b) Stochastic effects due to low doses ~ cancer development • Genetic effects (offspring-related) Stochastic in nature

35. Biologic effects of radiation • Somatic effects (own-body related) a) Early effects due to acute high doses = “deterministic effects” b)Stochastic effects due to low doses ~ cancer development • Genetic effects (offspring-related) Stochastic in nature

36. Deterministic effects • Due to acute & high dose radiation • Basically accidental situation • Appears after some hours to some weeks • Because depletion of cells in important organs (death cell / impairing cell division) • Organs such as • bone marrow • digestive track • brains

37. Deterministic effects • Major characteristics of deterministic effects: • There is a threshold of dose below which the effects will not be observed. • Above this threshold, the magnitude of the effect (= “severity”) increases with dose. • The effect is clearly associated with the radiation exposure. Ref: Stabin, 2008

38. Deterministic effects • Dose ~ 1 Gy radiation sickness • Dose < 1.5 Gy probab no early death • Dose ~ 2 Gy could lead to death after 2 wks • 30LD50 ~ 3-4 Gy (or …5 with med care) for man • deadly dose for 50% of exposed people within 30 days • Dose 3 - 10 Gy infection death • Above 10 Gy death after 3 à 5 days • Still higher doses: CNS death

39. Biologic effects of radiation • Somatic effects (own-body related) a) Early effects due to acute high doses = “deterministic effects” b) Stochastic effects due to low doses ~ cancer development • Genetic effects (offspring-related) Stochastic in nature

40. Stochastic Somatic effects • After certain weighting period can lead to cancer (solid cancers / leukemia) • Based on observation of • Atom bomb survivors • Radiologists • Radiation therapy patients • Uranium mine workers etc • Based on radiobiological research

41. Stochastic Somatic effects • Actually extrapolation from ~ medium & high level doses • Effects below ~ 100 à 200 mSv limited statistical significance • Difficulty to estimate risk: • Long & variable waiting period (5…30y or more) • Radiation-driven cancers indistinguishable from other cancers • Human tests/experiments not justified • Animal tests/experiments not directly transferable to humans

42. Stochastic Somatic effects LNT hypothesis Curves for individual Probability to get malignant/lethal cancer = f (dose equivalent)

43. Stochastic Somatic effects • Existence “adaptive response” & hormesis recognized, but insufficient exact justification to form basis for norms & standards • For low doses, also dose rate is important:  correction factor DDREF: Dose & Dose Rate Effect Factor

44. Stochastic Somatic effects Slope of LNT line: ~ 5 % per Sv ~ 5 x 10-5 per mSv or 105 people with 1 mSv  5 radiation induced cancers

45. Stochastic Somatic effects BEIR VII 2006

46. Stochastic Somatic effects BEIR VII 2007 deaths Number of cases or deaths per 100,000 exposed persons  5 - 7 x 10-5 per mSvfatal cancers (solid & leukemia)DDREF= 1.5 Nuclear Energy 2011-2012 William D’haeseleer

47. Stochastic Somatic effects • LNT disputed…by some authoritative scientists… • Considered to be an overestimate Nuclear Energy 2011-2012 William D’haeseleer

48. Viewpoint French Academy of Sciences and Academy of Medicine… Nuclear Energy 2011-2012 William D’haeseleer

49. American Scientists defending BEIR VII, US academy of Sciences… Nuclear Energy 2011-2012 William D’haeseleer

50. Stochastic Somatic effects Formal ICRP Recommendation 2007 Hence ~ 5 % / Sv or 50 ppm / mSv A D Wrixon, “New ICRP recommendations”, Journal of Radiological Protection28, 2008, 161–168 doi:10.1088/0952-4746/28/2/R02 Available at: http://iopscience.iop.org/0952-4746/28/2/R02/pdf/0952-4746_28_2_R02.pdf Nuclear Energy 2011-2012 William D’haeseleer