Biological Effects of Ionising Radiation

1. Biological Effects of Ionising Radiation Janice Brock University RPO

2. Janice Brock University RPO

3. Chemical composition : Water 70% Proteins 18% Fatty Substances 5% Carbohydrates, including sugars 2% DNA and other nucleic acids 1% Others 4% Janice Brock University RPO

4. Deoxyribonucleic Acid - Cytosine Adenine Guanine Thymine Janice Brock University RPO

5. Potential Chromosome Damage Janice Brock University RPO

6. In a biological system, ionisation of a molecule can lead to Direct or Indirect damage to the system. Janice Brock University RPO

7. Direct Damage 1 – cell may be undamaged 2 – cell may repair and work normally 3 – cell repaired but abnormal 4 – cell may die Janice Brock University RPO

8. Indirect Damage Ionising radiation causes cleavage of a covalent bond, fragmenting the molecule, each fragment retaining one of the paired electrons or by instigating chemical changes which produce free radicals. This damage to the system depends on the concentration of free radicals and this in turn depends on the number of ionisation events per unit mass. Janice Brock University RPO

9. Quantifying the damage: Energy required to produce a single ionisation event is afew tens Ev Ionising radiation generally has energy of keV or MeV. Potential for a great many ionisation events. The unit of Absorbed Dose (DT) is Gray. 1 Gray = Dissipation of 1 Joule/kg. Janice Brock University RPO

10. Equivalent Dose (HT ) and Radiation Weighting Factor (WR ) -particle 50 ionisations/nucleus -particle 12,500 ionisations/nucleus Janice Brock University RPO

11. Equivalent Dose (HT) and Radiation Weighting Factor (WR ) Equivalent Dose is a measure of the biological damage: HT = WR DT Unit is the Sievert (Sv) Janice Brock University RPO

12. Each type of radiation has been given a ‘Radiation Weighting Factor’ (WR) : Alpha Particles 20 Beta Particles 1 Photons 1 Neutrons 5 - 20 Janice Brock University RPO

13. Effective Dose (E) and Tissue Weighting Factor (WT ) • Effective Dose for any particular organ is given by: • E = WT HT • And if more than one organ is involved: • E = T WT HT Janice Brock University RPO

14. We use ‘effective dose’ when there is a non-uniform irradiation of the body. Janice Brock University RPO

15. The Effects on Health Deterministic and Stochastic Effects Deterministic Effects Radiation doses involved here are usually substantial and delivered over a short space of time and there is a threshold dose below which no clinical effect is observed. These type of effects are called Deterministic. Janice Brock University RPO

16. Stochastic Effects Since the probability for cancer at high doses increases with increasing dose, this relationship is assumed to hold true with low doses. This type of risk model is called stochastic. Stochastic Effects - No lower dose limit Probability of effect 2 prediction models Janice Brock University RPO

17. Additive Model A given dose produces a risk that is constant with time. Multiplicative Model A given dose produces a risk which is a constant multiple of the pre-existing spontaneous risk of cancer. Janice Brock University RPO

18. Molecular Damage to enzymes, DNA etc. and interference to biological pathways Subcellular Damage to cell membranes, nucleus, chromosomes etc. Cellular Inhibition of cell division, cell death, transformation to a malignant state Tissue, Organ Disruption to central nervous system, bone marrow, intestinal tract. Induction of cancer Whole Animal Death; 'radiation lifeshortening‘ Populations Changes in the genetic characteristics of individual members Important Radiation Effects Janice Brock University RPO

19. Acute (short-term) vs chronic (long-term) effects Janice Brock University RPO

20. Summary : Deterministic Effects - The risk is more or less certain. Stochastic Effects - The risk is not certain - a ‘probability’ exists. Additive model - The risk is constant in time. Multiplicative model - The risk is a constant multiple of the spontaneous risk. The model introduced in 1990 is the Multiplicative model. Janice Brock University RPO

21. There are at least three ways to measure the effect of radiation : Becquerels(Bq) Grays (Gy) Sieverts (Sv) Janice Brock University RPO

22. Risk Factors: ICRP 1990 Fatal cancers - 4%/Sv - , X or  only Non-fatal cancer - 1.2%/Sv Genetic factors - 0.6%/Sv Overall - 5.8%/Sv Janice Brock University RPO

23. Estimated Years of Life Expectancy Lost 7 6.5 6 5 4 Estimated Years Lost 3 2.7 2 0.76 0.9 0.83 1 0.13 0.12 0.15 0.09 0 Quarrying Agriculture Mining and 1 mSv/yr for 70 Government day cigarettes a Smoking 20 years Construction Radiation - Radiation – Overweight by 20% 3.4 mSv/yr for 30 years Manufacturing Janice Brock University RPO Industry Type Or Activity

24. A 5 hour flight by jet aircraft Cancer (Cosmic Rays) Living for 2 weeks in a granite building Cancer (radioactivity) Travelling 100 km by car Road Accident Travelling 1,000 km by air Accident Smoking 1 - 3 cigarettes Cancer & Lung Disease Drinking a half bottle of wine Liver & Other Disease Working as a Radiographer for 1 month Cancer (X-Rays) Working as a Radiologist for 2 weeks Cancer (X-Rays) Risk in perspective – Scenarios with one in million chance of death: Janice Brock University RPO

25. Conclusions Regarding Health Risk Janice Brock University RPO

26. Radiation Contamination, Brazil 1987 Cesium Capsule Left Behind. 2 Years Later, Capsule Removed. Localised burns and arm amputation. Object Sold to Junk Yard Owner. Workers opened lead casing, 2 died. Janice Brock University RPO

27. Radiation Contamination Continued : Scraped dust from source. Daughter ate, absorbing radioactive material. Daughter applied “blue powder” to body. Worker painted blue cross on his skin. Junk yards wife noticed people becoming ill. Scrap metal sold to another scrapyard. Janice Brock University RPO

28. Radiation Contamination Continued : Scrap metal taken on bus to hospital. Object placed in garden. Physicist confirmed presence of radioactivity. Wife died month later. Janice Brock University RPO

29. Other affected persons Janice Brock University RPO

30. Resulting Legalities: 3 Charged with criminal negligence Shows importance of record keeping Janice Brock University RPO

31. Treatment Whole Body v Partial Body Exposure Janice Brock University RPO

32. Exposure Levels and Symptoms 0.05 - 0.2Sv No symptoms 0.2 - 0.5Sv No noticeable symptoms 0.5 - 1Sv Mild radiation Sickness 1 - 2Sv Light radiation poisoning, 10% Fatality after 30 days 2 - 3Sv Moderate radiation poisoning, 35% fatality after 30 days Janice Brock University RPO

33. 3 - 4Sv Severe radiation poisoning, 50% Fatality after 30 days 4 - 6Sv Acute Radiation Poisoning, 60% Fatality after 30 days 6 - 10Sv Acute radiation poisoning, Near 100% Fatality after 14 days 10 - 50Sv Acute radiation poisoning, 100% Fatality after 7 days Exposure Levels and Symptoms Janice Brock University RPO

34. The mouth of a man who has suffered a 10 to 20 Gy dose 21 days after the exposure, note that damage to normal skin, the lips and the tongue can be seen. Janice Brock University RPO

35. The Conqueror, 1956 Did John Wayne die of cancer caused by a radioactive movie set? Janice Brock University RPO

36. The crater-scarred landscape of the Nevada Test Site. Janice Brock University RPO

37. Summary: • Ionising radiation causes damage at the cellular level • Absorbed dose (D) gives a measure of the damage • Unit is the Gray 1 Gy = 1 J/Kg • Equivalent dose (H) accounts for different types of radiation • Equivalent dose = Absorbed Dose x Radiation Weighting Factor • Unit is the Sievert e.g. for beta 1 Sv = 1 Gy Janice Brock University RPO

38. Summary Continued: Effective dose (E) is used for single organ doses Effective dose = Equivalent dose x Tissue Weighting Factor Unit is the Sievert (Sv) Deterministic effects are known effects above a certain dose Stochastic effects have a probability of occurrence Janice Brock University RPO