Lecture : Ionizing Radiation, its Risks and Biological Effects

1. IAEA Training Course on Basic Radiation Protection and Regulation Lecture: Ionizing Radiation, its Risks and Biological Effects

2. Objective To achieve an understanding of: • the hazards and biological consequences of ionizing radiation • the units of measurement to control biological consequences • the legal perspective on the hazards and biological consequences.

3. Contents • Early radiation health effects • Ionizing Radiation • Ionizing radiation and DNA damaga and repair • Radiation dose, dose units and dose limits • Radiation measurement • Biological effects – deterministic, stochastic and hereditary • Radiation exposure vs contamination • Controlling the hazard (time, distance, shielding)

4. I want to start by telling you a story that starts more than 500 years ago in a town in Bohemia which is now part of the Czech Republic. • The town is Jachymov (formerly St Joachimsthal)

5. Nowadays, if you visit… • Radon Palace Hotel, Jachymov, Czech Republic • Complex Curie, Jachymov, Czech Republic

6. But historically, Jachymov in the Ore Mountains was known for its silver mining The silver was minted into coins called “thalers” Over the centuries, the word ‘Thaler’ has Evolved into the word ‘dollar’

7. The waste ore from the silver mining was named pechblend (“bad luck rock”) Agricola Agricola wrote De Re Metallica (pub. 1556) and noted that miners from the region suffered from a strange lung disease: “Their lungs rot away”

8. Although it wasn’t understood at the time, this is thought to be the earliest recorded instance of the adverse health effects of ionizing radiation, that is, lung cancer induced in miners from the inhalation of radioactive radon gas.

9. Waste ore from Jachymov was used by Becquerel who discovered radioactivity in 1896 • While studying phosphorescence, Henri Becqerel discovered that uranium salts (in waste ore from St. Joachimsthal) blackened a photographic plate. • It was clear that he had discovered a form of radiation that could pass through paper and that caused the plate to become black. Image of Becquerel's photographic plate which has been fogged by exposure to radiation from a uranium salt. The shadow of a metal Maltese Cross placed between the plate and the uranium salt is visible.

10. Waste ore from Jachymov was used by Marie Curie who discovered Radium in 1896 • Marie Curie (1867-1934), discovered radium (and later polonium) in waste ore from St. Joachimsthal • Nobel Prize in Physics in 1903 • Nobel Prize in Chemistry in 1911

11. In 1985, one year before the discoveries of Becquerel and Curie, Roentgen discovered X-rays • In 1895, Wilhelm Roentgen demonstrated X-rays by showing a radiograph of a hand with a ring • In 1896, X-rays were turned to medical use to discover a needle in a hand • Since they were generated by using electricity with a cathode ray tube, X-rays were seen as a kind of electromagnetic radiation

12. Roentgen and Becquerel had both discovered mysterious rays that penetrated solid objects Curie had discovered a chemical element that had similar properties These ‘rays’ were both ionizing electromagnetic radiation and highly energetic (ionizing) radioactive particles Lets first look at ionizing electromagnetic radiation

13. What do we mean by ionizing radiation?

14. Emissions from radionuclides, whether alpha or beta particles or gamma rays also have sufficient energy to cause ionization. Whether we are talking about radioactive particles or electromagnetic radiation, what is key for our discussion is the subject of ionization

15. So what is ionization? • Ionization is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons to form ions, often in conjunction with other chemical changes. Whether an electromagnetic wave, or a radioactive particle, the ionizing radiation physically dislodges orbital electrons to form ions.

16. Cells, chromosomes and DNA

17. Why does ionization matter? • Radiation damages the cell by damaging DNA molecules • directly through ionizing effects on DNA molecules or • indirectlyby ionizing other molecules that form free radicals that in turn may damage DNA. Indirect Direct

18. What happens when DNA is damaged? • Normally, when cells divide to reproduce, an exact copy of the cells’ chromosomes is created for the new cell. • However, if the DNA in the chromosome is damaged, the instructions that control the cell’s function and reproduction are also damaged. • The ionizing radiation: • may pass directly through the cell without causing any damage, • may damage the DNA which may then repair itself, • may kill the cell • may affect the cell’s ability to reproduce itself correctly, possibly causing a mutation. • If the cell reproduces instead of dying, a new mutated cell may be produced. In many cancers, the instructions that turn off cell growth are somehow damaged causing out of control cell reproduction, creating a tumour • The death of one cell is of no concern but if too many cells in one organ, such as the liver, die at once, the organism will die.

20. Cell death, delayed effects and DNA repair • The bad news is that high doses of ionizing radiation may kill the cell outright and… • …radiation damage may not cause any outward signs of injury in the short term, but its effects may appear much later in life. The good news is that cells have DNA repair processes and… • …a lower dose delivered through a long period of time theoretically allows the cells of the body the opportunity to repair themselves.

21. How do cells protect themselves against DNA damage?

22. So, generally speaking, how are organs and tissues affected by low doses of ionizing radiation? • Low doses of ionizing radiation cause DNA damage, most of which is repaired, but there is a potential for mutations and long-term health effects (i.e. cancer). These are called stochastic effects (meaning that their probability of occurrence increases with dose, while the severity is independent of dose).

23. How are organs and tissues affected by high doses of ionizing radiation? • High doses of ionizing radiation can cause so much DNA damage that the cell’s repair mechanisms can be overwhelmed. These are called non-stochastic or deterministic effects (i.e. radiation burns, acute radiation syndrome, etc. These effects are almost certain to occur above a threshold dose, and their severity increases with dose.)

24. What is radiation dose? • It is the energy deposited by radiation in tissue • Radiation dose depends upon several factors: • the type of radiation: alpha, beta, gamma or neutron and the associated radiation quality factor and • the organ or tissue in which the ionizing radiation deposits its energy and the related organ or tissue weighting factors • Alpha radiation is mainly a hazard if it is ingested or inhaled • Beta radiation maybe hazardous to the skin or internally • Gamma radiation is highly penetrating • Dose limits decreased by stages several times throughout the 20th Century

25. Ionization and Radiation Weighting Factors • Different forms of ionizing radiation have differing abilities to generate biologic damage. These are shown in the table below.

26. Organ and Tissue Weighting Factors Usually the radiation dose is delivered to the whole body, however sometimes individual organs and tissues receive the dose of ionizing radiation and the organ or tissue weighting factors permit the effective dose to be calculated. (2007 values are in parentheses in diagram)

27. Radiation Units: Becquerels, Grays and Sieverts • The source activity in Becquerels maybe thought of as the number of throws: usually a large number and in all directions (often kilo or mega-Becquerels) • The Gray is a measure of the absorbed dose, the energy deposited by ionizing radiation in the target (the other kid) and may be thought of as the number of hits (typically in milligrays or micrograys) • The Sievert (Sv) is a measure of equivalent dose. It is a measure of the biological effect of the ionizing radiation and is influenced by the radiation weighting factor or quality factor such that, for example, ‘alpha balls’ have 20 times the impact of ‘gamma balls’ • The Sievert (Sv) is also a unit of effective dose and it is a measure the biological effect of the ionizing radiation on all the organs and tissues. (A hit on the foot does not have the same impact as a ball in the face)

28. If taken internally, some radionuclides are more biologically important than others • When ionizing radiation is taken into the body and is absorbed into tissues or taken up by organs it may give radiation dose to those organs and tissues over a long period of time. • For example, radium taken into the body behaves chemically like calcium and is incorporated into bones and teeth where it decays slowly and gives radiation dose to those organs and tissues over many years. • This is called the committed effective dose.

29. Factors that influence the committed effective dose • The quantity of radionuclide • The radionuclide half-life • The decay scheme of the radionuclide (its emission type and energy) • The chemical state of the radionuclide • The chemical behavior in the body • Does the radionuclide concentrate in the body? • Its ultimate location in the body • The rate of excretion Radiation doses from inhalation and absorption for hundreds of radionuclides are catalogued as Annual Limits on Intake

30. Radiation dose is measured (and regulated) in units known as millisieverts • Rolf Sievert was a Swede who in the 1920s proposed at way to measure radiation dose • Worldwide scientific bodies proposed radiation dose limits beginning in the 1930s and they still do so today • These scientific recommendations for radiation dose limits are incorporated into national legislation

31. Dose Limits One should be aware that limits for occupational and public exposure will usually be prescribed in the regulations as either: • effective dose limits (whole body); and • equivalent dose limits for specific organs such as the skin, lens of the eye and the extremities.

32. Occupational Dose Limits Recommended limits from the IAEA Basic Safety Standards (GSR Part 3) mSv – millisievert. Compared to the average annual dose fromnatural backgroundradiationof ~ 2.4 millisievert per year (UNSCEAR)

33. Public Dose Limits Recommended limits from the IAEA Basic Safety Standards (GSR Part 3) Note that these regulatory dose limits DO NOT pertain to patients. They pertain to workers and to the non-patient public only.

34. Measuring Radiation Radiationmeans the photons (gamma or x-rays) and particles emitted by radioactive sources during decay, or from electrically generated sources (e.g. x-ray equipment, linear accelerators, etc.) • Radiation is measured as adose(Gy) or asdose rate(Gy/h) • Sievert (Sv) is the SI unit ofequivalent doseandeffective dose, equal to 1 J/kg and Gray (Gy) is the SI ofabsorbed dose, equal to 1 J/kg • However, smaller fractions of these units are often used, e.g. microgray per hour (µGy/h) or millisievert per hour (mSv/h).

35. In practice, how is radiation dose measured? • Personal dosimeters • TLD’s and film badges • Neutron dose measurements • Bioassay measurements • Personal alarming dosimeters • Radiation survey meters

36. Radiation dose measurement devices

37. Biological Effects Deterministic Effects • are the result of high doses; • have a threshold before they appear; • appear early (and/or late); • have a severity depending on the dose. Stochastic Effects • may arise from any dose; • have no known threshold; • have a long latency period; • have a probability of occurrence depending on the radiation dose.

38. Elbow injury from irradiator accident Severity of Effect Burn from very high dose interventional x-ray procedures Threshold Dose Deterministic Effects - Example

39. Whole body acute doses for deterministic effects

40. Symptoms of Acute Radiation Syndrome (a deterministic effect) • Loss ofappetite • Nausea • Fatigue • Diarrhoea • Vomiting • Loss ofhair • Nosebleeding • Sub-cutaneousbleeding • Anaemia • Infection • Death

41. Deterministic Effects - Example Acute Radiation Effects – Chernobyl 1986 Chernobyl. Ten Years On. Nuclear Energy Agency OECD Nov 1995 Table 6

42. Stochastic Effects (e.g. cancer) The possibility that a cancer (or hereditary effect) might have been caused by exposure to ionizing radiation poses considerable challenges. • The adverse outcome might be due to some other agent, known or unknown. • There is likely to have been a lengthy period of time between the alleged cause (the radiation exposure) and the adverse outcome. • Stochastic effects are probability based with the risk of occurrence increasing with dose.

43. Stochastic Effects and Risk • Estimates of risk are based on studies of people who wereexposed to fairly high radiation doses.They include the survivors of the atomic bombs in Japan, patients exposed to radiation for treatment or diagnosis of disease, and groups of workers in some industries. • In radiation protection it isassumedthat however low the dose there is some risk of harmful effects and that the risk is proportional to dose.

44. Doses where cancers have been observed Doses of relevance in radiation protection The Radiation Dose Response Relationship

45. No hereditary effects of ionizing radiation have been observed in humans Hereditary Effects have only been observed in animal populations exposed to relatively high doses of radiation, although they are also presumed to occur in humans.” UNSCEAR 2008: However, Ionizing radiation is a universal mutagen and experimental studies in plants and animals have clearly demonstrated that radiation can induce genetic effects; consequently, humans are unlikely to be an exception.

46. Risks Risks associated with practices involving radioactive materials may be a result of either: • exposure to the emitted radiation; or • contamination

47. Exposure Exposure to radiation, such as this patient being exposed to gamma radiation (from Cobalt-60) during radiotherapy treatments,does not make the individual radioactive. Note:Exposure to some neutrons or to very high energy photons may induce radioactivity.

48. Surface contamination monitor Wipe test for removable contamination Contamination Contamination is the presence of uncontained radioactive material on surfaces where it should not be found. • Contamination may be: • fixed; or • removable (non-fixed)

49. Contamination Contamination most frequently arises from poor working practices with unsealed radioactive sources (e.g. in research, nuclear medicine and well logging tracer applications). • It also may be caused by leaking sealed sources (where the radioactive material breaches its encapsulation). • Skin and clothing can be contaminated (causing exposure). • Contamination also might be inhaled, ingested, or absorbed though the skin.

50. The Radiation Hazard • The hazard from ionizing radiation may be due to whole or partial body exposure. • Being exposed to ionizing radiation does not (normally) make you radioactive. • Fixed radioactive contamination presents an external radiation hazard. • Non-fixed radioactive contamination presents both an external and internal radiation hazard. • Radioactive material taken into the body presents a potential long-term exposure hazard.