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IAEA International Atomic Energy Agency Biological Effects of Ionizing Radiation Michael Hajek Radiation Safety and Monitoring Section Division of Radiation,

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Presentation on theme: "IAEA International Atomic Energy Agency Biological Effects of Ionizing Radiation Michael Hajek Radiation Safety and Monitoring Section Division of Radiation,"— Presentation transcript:

1 IAEA International Atomic Energy Agency Biological Effects of Ionizing Radiation Michael Hajek Radiation Safety and Monitoring Section Division of Radiation, Transport and Waste Safety Department of Nuclear Safety and Security

2 IAEA Outline Introduction and historical background Targets for biological radiation damage Deterministic and stochastic effects ICRP system of radiological protection Biological Radiation Effects2

3 IAEA Ionizing Radiation Ionizing radiation −Composed of particles that individually carry enough kinetic energy to liberate an electron from an atom or molecule −Kinetic energy > 12.4 eV Biological Radiation Effects3 Non-ionizing radiationIonizing radiation Ionization energy of soft tissue 12.4 eV or 100 nm

4 IAEA Discovery of Ionizing Radiation X-rays (1895)Natural radioactivity (1896) Wilhelm Conrad Roentgen Antoine Henri Becquerel Nobel Prize in Physics 1901Nobel Prize in Physics 1903 Biological Radiation Effects4

5 IAEA First Medical Observations Skin-burn attributed to radiation ─ 1901 Radiation-induced leukaemia ─ 1911 Clinical syndrome following exposure to atomic bomb explosions ─ 1946 P. D. Keller, J. Am. Med. Assoc. 131, 504 (1946). Holzknecht’s chromoradiometer related to skin erythema ─ 1902 Biological Radiation Effects5

6 IAEA Targets for Biological Radiation Damage Human tissues are formed from cells that are grouped into organs and systems of the body to perform the many specialized functions Each cell is defined by a membrane enclosing −Cytoplasm containing up to 85% water −Structures such a nucleus Biological Radiation Effects6

7 IAEA Chromosomes and DNA Chromosomes are organized structures of supercoiled deoxyribonucleic acid (DNA) and proteins found in cells DNA macromolecules encode genetic information used in development and functioning of all known living organisms Biological Radiation Effects7

8 IAEA Structure of DNA Double-stranded helices, with nucleobases (G, A, T, C) attached to sugar-phosphate backbones Each type of nucleobase on one strand bonds with just one type of nucleobase on the other strand (complementary base pairing) Biological Radiation Effects8 Hydrogen bond 3.4 nm 1 nm

9 IAEA Direct and Indirect Radiation Effects Indirect action predominant with low-LET radiation (X- and gamma rays) Direct action predominant with high-LET radiation (alpha particles) Biological Radiation Effects9

10 IAEA Consequences of DNA Damage Biological Radiation Effects10 DNA damage MutationCell deathRepair Stochastic effectDeterministic effectViable cell

11 IAEA Mechanism of DNA Repair DNA damage occurs at a rate of ~ 100,000 per cell per day Genetic mutations drive evolution Biological Radiation Effects11

12 IAEA Deterministic Radiation Effects Occur at high doses when enough cells in an organ or tissue are killed or prevented from functioning normally −Threshold dose, above which effects are clinically observable −Severity increases with dose −Acute effects, non-malignant late effects −Examples: Cataracts, erythema, acute radiation syndromes (ARS) Biological Radiation Effects12 DOSE SEVERITY 100% Threshold dose

13 IAEA Deterministic Radiation Effects Data on deterministic radiation effects come from −Survivors of atomic bombs on Hiroshima and Nagasaki −Effects on early radiologists −Consequences of severe accidents with industrial radiation sources −Studies of side effects of radiotherapy Biological Radiation Effects13

14 IAEA Organ or tissueAcute dose (Gy)Type of effectTime of occurrence Bone marrow1ARS1 to 2 months Skin3Erythema1 to 3 weeks Thyroid5Hypothyroidism≥ 1 year Lens of the eye2Cataract≥ 6 months Gonads3Permanent sterilitySeveral weeks Foetus0.1Teratogenesis─ Deterministic Radiation Effects Biological Radiation Effects14

15 IAEA Deterministic Effects after Chernobyl Chernobyl experience −ARS and radiation burns Biological Radiation Effects15

16 IAEA Stochastic Radiation Effects Occur at all dose levels as a result of damage to the DNA −Random or non-threshold effects −Probability of occurrence increases with dose −Late effects, often decades after exposure −Examples: Radiation-induced cancers, hereditary effects Biological Radiation Effects16 DOSE RISK Linear-no-threshold hypothesis Quadratic response

17 IAEA Stochastic Radiation Effects Principal sources of information on stochastic effects are −Epidemiological studies on atomic-bomb survivors −Patients exposed to radiation for medical treatment or diagnosis −Some groups of occupationally exposed workers (uranium miners, nuclear industry workers, radium-dial painters) Biological Radiation Effects17

18 IAEA Stochastic Radiation Risks Biological Radiation Effects18 DOSE RISK Risk factor Relationship is irrelevant Background incidence Background dose Average2.4 mSv Typical 10. mSv High100. mSv Increment of dose Increment of probability

19 IAEA ICRP Nominal Risk Coefficients ICRP detriment-adjusted nominal risk coefficients (10 −2 Sv −1 ) for stochastic effects after exposure to radiation at low dose rate Combined detriment due to excess cancer and hereditary effects ~ 5% per Sv Biological Radiation Effects19 Exposed populationCancerHereditary effectsTotal Publ.103Publ. 60Publ.103Publ. 60Publ.103Publ. 60 Whole5.56.00.21.35.77.3 Adult4.14.80.10.84.25.6

20 IAEA ICRP System of Radiological Protection … to contribute to an appropriate level of protection for people and the environment against the detrimental effects of radiation exposure... Justification −Any decision that alters the radiation exposure situation should do more good than harm. Optimization (ALARA) −The likelihood of incurring exposure, the number of people exposed, and the magnitude of their individual doses should all be kept as low as reasonably achievable, taking into account economic and societal factors. Limitation −The total dose to any individual from regulated sources in planned exposure situations other than medical exposure of patients should not exceed the appropriate limits specified by the Commission. Biological Radiation Effects20

21 IAEA Philosophy of Individual Dose Limitation Prevention of deterministic effects −Dose limits lower than threshold Reduction of stochastic effects to acceptable level −Comparison with risks for other occupations −Ethical judgment Biological Radiation Effects21 Annual dose limits Occupational exposure→20 mSv(whole-body exposure) → 20 mSv(lens of the eye), 500 mSv (extremities) General public→ 1 mSv(whole-body exposure) → 15 mSv(lens of the eye), 50 mSv (skin) Annual dose limits Occupational exposure→20 mSv(whole-body exposure) → 20 mSv(lens of the eye), 500 mSv (extremities) General public→ 1 mSv(whole-body exposure) → 15 mSv(lens of the eye), 50 mSv (skin)

22 IAEA Further Information IAEA Safety Standards −No. GSR Part 3 (Interim) “Radiation Protection and Safety of Radiation Sources: International Basic Safety Standards” (2011) IAEA Safety Standards Series −No. SF-1 “Fundamental Safety Principles” (2006) −No. RS-G-1.1 “Occupational Radiation Protection” (1999) Practical Radiation Technical Manuals −“Health Effects and Medical Surveillance” (2004) −“Personal Protective Equipment” (2004) Biological Radiation Effects22

23 IAEA Thank you for your kind attention! Biological Radiation Effects23


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