1. 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. Outline Introduction and historical background
Targets for biological radiation damage
Deterministic and stochastic effects
ICRP system of radiological protection
Biological Radiation Effects

3. Ionization energy of soft tissue
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
Non-ionizing radiation
Ionizing radiation
Ionization energy of soft tissue
12.4 eV or 100 nm
Biological Radiation Effects

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

5. 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 Effects

6. 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 Effects

7. 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 Effects

8. 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)
Hydrogen bond
1 nm
3.4 nm
Biological Radiation Effects

9. 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 Effects

10. Consequences of DNA Damage
Repair
Cell death
Mutation
Viable cell
Deterministic effect
Stochastic effect
Biological Radiation Effects

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

12. 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)
DOSE
SEVERITY
100%
Threshold dose
Biological Radiation Effects

13. 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 Effects

14. Deterministic Radiation Effects
Organ or tissue
Acute dose (Gy)
Type of effect
Time of occurrence
Bone marrow 1
ARS
1 to 2 months
Skin 3
Erythema
1 to 3 weeks
Thyroid 5
Hypothyroidism
≥ 1 year
Lens of the eye 2
Cataract
≥ 6 months
Gonads
Permanent sterility
Several weeks
Foetus
0.1
Teratogenesis ─
Biological Radiation Effects

15. Deterministic Effects after Chernobyl
Chernobyl experience
ARS and radiation burns
Biological Radiation Effects

16. 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
DOSE
RISK
Linear-no-threshold hypothesis
Quadratic response
Biological Radiation Effects

17. 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 Effects

18. Stochastic Radiation Risks
DOSE
RISK
Risk factor
Relationship is irrelevant
Background incidence
Background dose
Average 2.4 mSv
Typical 10. mSv
High 100. mSv
Increment of dose
Increment of probability
Biological Radiation Effects

19. 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
Exposed population
Cancer
Hereditary effects
Total
Publ.103
Publ. 60
Whole
5.5
6.0
0.2
1.3
5.7
7.3
Adult
4.1
4.8
0.1
0.8
4.2
5.6
Biological Radiation Effects

20. 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 Effects

21. 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
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)
Biological Radiation Effects

22. Further Information IAEA Safety Standards IAEA Safety Standards Series
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 Effects

23. Thank you for your kind attention!
Biological Radiation Effects