Biological Effects of Ionizing Radiation

Training Course on Radiation Protection for Radiation Workers and RCO’s of BAEC, Medical Facilities & Industries - 2021�

1. Training Course on Radiation Protection for Radiation Workers and RCO’s of BAEC, Medical Facilities & Industries - 2021 Biological Effects of Ionizing Radiation Siddha Moutoshi Shome Principal Geologist Health Physics and Radioactive Waste Management Unit, Institute of Nuclear Science and Technology, AERE, BAEC, Savar, Dhaka . 25/10/2021 1

2. Contents Introduction Human Exposure Pathways Biological Effects Stochastic Effects Deterministic Effect Somatic Effect Genetic Effects Early and Late Effects Acute and Chronic Exposures Summary of Radiation Effects Principles of Radiation Protection 2

3. Introduction Radiation: is an energy in the form of electromagnetic waves or high-speed particles, traveling in the air. Radioactivity: spontaneous emission of radiation from the nucleus of an unstable atom. Ionizing Radiation: is radiation that has sufficient energy to remove electrons from atom. Example- Alpha, beta, gamma etc. Non-ionizing Radiation: refers to any type of electromagnetic radiation that does not carry enough energy to ionize atoms or molecules. Example - Radiowaves , Visible light etc. 3

4. Cont’d.. Ionizing radiations have many beneficial applications (Ex-X-ray), but they also may have detrimental consequences for human health and for environment. Radiation can cause biological damage on cells either direct or indirect action. Direct action: Ex - direct interaction with DNA. Indirect action: Radiation can also produce free radicals by ionizing water molecule of body. These radicals can further interact with DNA, RNA or protein molecules and can cause damage of tissues. To protect people and the environment it is essential to understand how radiation-induced effects occur. 4

5. α – rays neutrons Direct Action of Ionizing Radiation on DNA (High LET Radiations) 5

6. e - X ray  ray P + O H H OH - H + H ・ H O ・ Indirect (free radical) Action of Ionizing Radiation on DNA (Low LET Radiations) 6

7. Human Exposure Pathways There are two main categories of exposure pathway: External exposure pathways (the source of exposure remains outside the body) Internal exposure pathways (the source of exposure is incorporated into the body). 7

8. Biological Effects Damag e of cells: Cell death Abnormal cell division Permanent modification to cells 8

9. Factors of Radiation Damage The potential biological effects and damages caused by radiation depend on the conditions of the radiation exposure . Total dose A large dose given in a short amount of time: more damaging than the same dose given over a longer period of time Dose rate Part of the body exposed Uniformity of exposure Age of the victim 9

10. Biological Effects of Radiation Stochastic Effect Deterministic Effect Somatic Effect Genetic Effect 10

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12. Stochastic Effects Stochastic means random. It occurs in a statistical manner. No threshold dose. It can occur even at low doses. The probability of effect increases with increasing radiation dose. But the severity is not related to radiation dose. It can be further classified into somatic and genetic (hereditary) effect. 12

13. Stochastic Effects Examples- cancer and genetic effect Dose equivalent/ Sv Probability of Effect 13

14. Deterministic Effects Deterministic effects have a threshold dose. No effect observed below the threshold dose. But once the threshold exceeded, the severity of effect increases with increasing dose. Examples- cataract, reddening of skin, burns, hair loss, blood changes, temporary or permanent sterility, nausea, diarrhoea, etc. All are somatic effects. 14

15. Threshold Severity Dose Deterministic Effects 15

16. Cells Organs/tissues Damages Type Symptoms/signs Mechanisms DNA Mutation Germ cell Heredity effect Stochastic effect Mutation of single cell Somatic cell Cancer Apoptosis or Necrosis Germ cell Infertility Deterministic effect Cell death Somatic cell Loss of function (Skin injury, ARS ） Stochastic and Deterministic Effects 16

17. Thresholds Tissue and effect Equivalent dose ( Sv ) Testes Temporary Sterility 0.15 Permanent Sterility > 3.5 Ovaries Sterility > 2.5 Lens of the eye Detectable Opacities > 0.5 Visual impairment (cataract) > 2.0 Source: ICRP 60 17

18. Cont’d.. Whole body and Effect Dose (Sv) Clinical blood changes 0.5 Sv LD 50/60. 50% die in 60 days Bone marrow depression ~ 3.0 Sv Death in 48 hours Central nervous system collapse ~100 Sv Source: ICRP 60 18

19. Classic Example of Stochastic and Deterministic Effects Stochastic effects - smoking & lung cancer. not everyone who smokes will develop it, but the risk increases with the number of cigarettes smoked. Deterministic effects - intake of alcohol. a person must exceed a certain amount of alcoholic intake before he/she begins to show the signs of drinking. 19

20. Somatic Effects Damage of ordinary cells Radiation effects that exposed individual suffers during their lifetime and the effect is only limited to the exposed person. 20

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22. Genetic Effects Damage of reproductive cells and appear only in the offspring of the irradiated person. Genetic damage is permanent and cannot be repaired. 22

23. Early and Late Effects Early Effects: Response that occurs within minutes or days after exposure. Example: Erythema, Radiation sickness (nausea, vomiting, diarrhea). 23

24. Early and Late Effects Late Effects: Response that occurs in months or years after exposure. May occur in person who have been exposed to acute exposure. May also arise from chronic exposure. Example: cancer, genetic effects, cataracts and sterility. 24

25. Latency Period The time that passes between being exposed to radiation and detection of radiation-induced effect (ex – cancer). Effects can be immediate or years later for acute, high level exposures. 25

26. Acute and Chronic Exposure Acute Exposure: A large amount of dose in a short period of time. Acute absorbed doses above about 1 Gy give rise to nausea and vomiting, known as radiation sickness and it occurs a few hours after exposure. Similarly, there is no well defined point above which death is certain, but the chances of surviving an acute dose of about 8 Gy would be very low. Chronic Exposure: Small amount of doses over a long period of time. 26

27. Acute Radiation Syndrome (ARS) A combination of clinical syndromes occurring in stages during a period of minutes / hours to weeks after exposure, as injury to various tissues and organs is expressed. The acute radiation syndrome is subdivided into three categories. In order of increasing severity, these are : (1) Hemopoietic syndrome, (2) Gastrointestinal syndrome, and (3) Central nervous system syndrome 27

28. Hemopoietic syndrome Signs appears after a whole body gamma dose of 2 Gy (200 rads) Symptoms start with anorexia, nausea, vomiting and followed by bone marrow depression and infection. 28

29. Gastrointestinal syndrome Signs appears following a total body dose of about 10 Gy (1000 rads) or greater. Early symptoms are severe nausea, vomiting, diarrhea and followed by complete destruction of bone marrow. Death within several weeks after exposure 29

30. Central nervous system syndrome Signs appears after a total-body gamma dose in excess of about 20 Gy (2000 rads) Damages the central nervous system as well as all the other organ systems in the body; Unconsciousness occurs within few minutes. Death occurs in hours to several days. 30

31. Summary of Radiation Effects Erythema ARS Hereditary Effects Cataract Cancer Sterility Early Effects Late Effects Acute Exposure Chronic Exposure RADIATION EXPOSURE 31

32. Principles of Radiation Protection Justification Optimization Dose limitation Risk < Benefit ALARA ( A s L ow A s R easonably A chievable) Parameters Workers ( mSv /y) Public ( mSv /y) Effective Dose 20 1 Equivalent Dose Lens of eye Skin Extremities 150 500 500 15 50 50 32

33. Thank You 33