Biological Effects of Ionizing Radiation

1. Biological Effects of Ionizing Radiation USACE BASIC RADIATION PROTECTION TRAINING

2. Overview • Stochastic vs. Non-stochastic Effects • Dose Response Curves • Mechanisms for Biological Damage • Direct vs. Indirect • Specific Biological Effects • Risk Estimates

3. Stochastic (Random) Effects • Occur by chance • Occur in both exposed and unexposed individuals • Probability of occurrence increases as dose increases

4. Non-stochastic (Deterministic) Effects • A certain minimum dose must be exceeded before occurrence • The magnitude of the effect increases as dose increases • There is a clear causal relationship between exposure and occurrence

5. Radiation Detriment • Stochastic Effects • Severity independent of dose (both somatic and genetic) • Examples: leukemia, malignant tumors • Non-stochastic Effects • Severity varies with magnitude of dose, above a threshold dose (somatic) • Examples: cataracts, fertility impairment

6. Linear No Theshold Response • Applies to stochastic effects • Assumes that any amount of radiation has some detrimental effect 1 Probability of Effect 0.5 0 0 50 100 Dose

7. 1 Probability of Effect Theshold Dose 0.5 0 0 50 100 Dose Nonlinear Theshold Response • Applies to non-stochastic effects

8. + + + + + + - - - - - - + + + + + + + + + + + + + + + + + + + + + + + - - - - - - - - - - - - - - - - - - - - - - - Linear Energy Transfer (LET) • The amount of energy deposited per unit path length • High LET Radiation is more damaging Low LET High LET

9. Cell Radiosensitivity • EM 385-1-80, Table 3-6 • Sensitivity Directly Proportional to Reproductive Capacity • Sensitivity Inversely Proportional to Cell Differentiation • White Blood Cells (Lymphocytes>Granulocytes) • Basal and Endothelial Cells • Sperm Producing Cells • Red Blood Cell Producing Cells

10. Direct Action • Radiation interacts directly with a molecule through excitation or ionization • The molecule dissociates • The effect depends on which molecule was affected

11. Direct Effects • Example: Direct interaction with DNA +

12. Indirect Action • The body is composed primarily of water and most direct action will be on water • This results in hydrolysis of water

13. H2O H2O+ + e- H2O+ + H2O H3O+ + OH Hydrolysis of Water • Radiation ionizes a water molecule • The ion reacts with another water molecule to form the highly reactive hydroxyl radical

14. Incident X-ray Photon Fast Electron (e-) Ion Radical Free Radical Chemical Changes for Breakage of Bonds Biological Effects Chain of Events for Indirect Action of Radiation

15. Cell Results • Damage is repaired • Cell Death • Inhibition of Cell Division • Inactivation of Enzymes • Alteration of Membrane Permeability • Chromosome Aberrations

16. Stochastic Effects • Cancer • Leukemia • Bone Cancer • Lung Cancer • Mental Retardation • Genetic Effects

17. Cancer • Cancer induction well documented at doses of 100 rad or more • Tumor induction time of 5-20 years • Radiation induced tumors most frequent in the hematopoietic system, thyroid, bone, and skin.

18. Leukemia • Most likely cancer from whole-body irradiation • Atomic bomb survivor data shows increase mortality at doses above 40 rad • Induction from lower doses is inconclusive

19. Bone Cancer • Primarily due to internally deposited radionuclides • Radium, Plutonium, Americium, and others are “bone seekers” • All bone seekers are known to cause cancer in laboratory animals if injected in sufficient quantity

20. Lung Cancer • Radiation induced lung cancer seen mainly in underground miners exposed to high Radon concentrations • Lung cancer risks at low doses are uncertain • Radiation induced lung cancer has been reported in atomic bomb survivors and some radiation therapy patients.

21. Mental Retardation • Has been observed in children exposed in-utero to radiation from the atomic bombs in Japan • Most pronounced in those exposed between the 8th and 17th week of pregnancy • Brain cells divide rapidly during this period

22. Genetic Effects • No radiation induced genetic effects have been observed in humans • Could occur if DNA is damaged

23. Non-stochastic Effects • Cataracts • Skin Erythema • Acute Effects • Hematopoietic Syndrome • Gastrointestinal (GI) Syndrome • Central Nervous System Syndrome

24. Acute Radiation Syndrome • A Large Gamma Radiation Dose in a Short Duration • LD50/30 = 450 rad • Lethal dose to 50% of population in 30 days without medical attention

25. Hematopoietic Syndrome • Blood changes may be seen at dose as low as 14 rad • Blood changes almost certain at doses above 50 rad • Hematopoietic Syndrome appears at about 200 rad • Characterized by depression or ablation of the bone marrow • May be accompanied by nausea and vomiting, fatigue, and increased temperature

26. Gastrointestinal Syndrome • Occurs at a whole body dose of 1000 rad or greater • Characterized by the destruction of the intestinal epithelium and complete destruction of the bone marrow • Accompanied by severe nausea, vomiting, and diarrhea soon after exposure • Death occurs within a few weeks

27. Central Nervous System Syndrome • Occurs at whole body doses of 2000 rad or more • Damages the central nervous system as well as all other organs and systems • Unconsciousness occurs within minutes • Death follows in a matter of a few hours to a few days

28. Risk Comparisons • Fatal risk of 1:1000000 (10-6) • 40 Tablespoons of Peanut Butter • 100 charcoal broiled steaks • 2 days in New York City • 1.5 Cigarettes • 10 mrem of radiation • 300 miles in a car • 1000 miles in a jet

29. Exposure Limits • Radiation Risk Model as the Basis For Current Limits • NRC Regulatory Guide 8.29, Instruction Concerning Risks From Occupational Exposure • NRC Limits Do Not Permit Large Acute Dose • Focus On Controlling Chronic Exposure For Which Possible Delayed Effects Are The Concern • 1 rem TEDE = 4 in 10,000 Risk Of Fatal Cancer • Worker’s Chance of Dying From Cancer Increases From 20% to 20.04%

30. Occupational Dose Limits • NRC 10 CFR Part 20 Annual Limits • Whole Body - 5000 mrem TEDE • OSHA 29 CFR 1910.1096 • Whole Body - 1,250 mrem TEDE/QTR • Special exposures to 3 rem in a QTR if total dose less than 5(N-18)

31. USACE Occupational Dose Limits • EM 385-1-80, Table 5-1, 10% of NRC Limits (500 mrem TEDE annually) • To Ensure Compliance With OSHA and Agreement State Requirements • May Be Extended to a Maximum of the NRC Limits With the Written Approval of the RPSO

32. USACE ALARA Limits • Doses Must Be As Low As Reasonably Achievable Taking Into Account Social, Technical, and Financial Factors • Small Projects Could Use 10% of the USACE Limits

33. NRC/USACE Declared Pregnant Worker Dose Limits • Section 20.1208 of 10 CFR Part 20, EM 385-1-80 Chapter 5-2b.(5) • 500 mrem During the Entire Gestation • Form for declaring pregnancy in the USACE is on page H-20 of EM 385-1-80 • Draft Regulatory Guide DG-8014 Instruction Concerning Prenatal Radiation Exposure

34. USACE Public Dose Limits • RPO responsible for ALARA principle • 100 mrem TEDE From Licensed Activities • EDE Shall Not Exceed 2 mrem in Any One Hour • Effluent Release Limits Based on 50 mrem/yr Airborne, 50 mrem/yr Water • ALARA level of 10 mrem/yr • 25 mrem/yr TEDE From a Decommissioned Facility • Drinking Water 4 mrem/yr EDE From , 

35. USACE Radiation Protection Regulations • ER 385-1-80 • EM 385-1-80 • ER 385-1-92 • EM 385-1-1 • CEGS 1351

36. Questions?