Radiation Biology

1. Radiation Biology Reading: Chapter 4

2. Radiation Biology • Radiation Biology is the study of the effects of radiation on living tissue. • X-rays are a form of ionizing radiation.When x-rays strike patient tissues, ionization results. • All ionizing radiations are capable of producing biologic changes in living tissue.

3. Effects of Ionization

4. Radiation Causes Ionization of: • ATOMS which may affect • MOLECULES which may affect • CELLS which may affect • TISSUES which may affect • ORGANS which may affect • THE WHOLE BODY

5. Theories of Radiation Injury: • Direct Theory • when radiation interacts with atoms of the DNA molecule, it may affect the ability of a cell to reproduce and survive. • Direct injuries from exposure to ionizing radiation occur infrequently.

6. Theories of Radiation Injury • Indirect Theory: • when x-ray photons are absorbed within the water inside a cell it can cause the formation of toxic substances. (water to hydrogen peroxide!) • This can ultimately lead to the destruction of the cell. • Injuries of this type occur frequently because our body cells contain so much water. (70 – 80% water!)

7. Free Radical Formation

8. Dose Response Curve • So…if ALL ionizing radiation is harmful, what level of exposure is considered “acceptable”? • With radiation exposure, a dose-response curve can be used to correlate the: • Response (or damage) to the tissue • With the: • Dose (or amount) of the radiation received

9. Dose Response Curve • Turn to page 36 in your books. • With radiation a “linear non-threshold” relationship is seen. • A LINEAR relationship indicates that the response of the tissues is DIRECTLY PROPORTIONAL to the dose level. • A non-threshold relationship indicates that a threshold lose level DOES NOT EXIST for radiation.

10. Threshhold Curve

11. Sequence of Radiation Injury • The Latent Period • The Period of Injury • The Recovery Period

12. The Latent Period • The latent period is defined as the time between exposure to x-rays, and the appearance of radiation damage. • This is the first step in the sequence of radiation injury.

13. The Latent Period • The latent period can be short or long depending upon: • Total dose of radiation received • The amount of time, or rate, it took to receive the dose. • As you may expect: • The MORE radiation received and • The FASTER the dose rate, • The SHORTER the latent period

14. The Period Of Injury • A variety of cell injuries may occur. • Cell death • Changes in cell function • Breaking or clumping of chromosomes • Formation of giant cells • Abnormal cell division or cessation of cell division

15. The Recovery Period • Not all cellular radiation injuries are permanent! • Most damage caused by low-level radiation injury is repaired within the body’s cells!! • Scatter Radiation remains in cells, but the body can slough it off in 24-48 hours. However, repeated exposure does not allow the body time to adjust.

16. There is a CUMULATIVE EFFECT • The effects of radiation exposure are additive, and unrepaired damage accumulates in the tissues. • The cumulative effects of repeated exposure can lead to health problems. • Cancer • Cataract formation • Birth defects • See table 4-1 at the bottom of page 37.

17. Factors Affecting Radiation Injury • Total Dose: • Greater damage with larger amounts of radiation • Dose Rate: • A high dose rate does not allow time for cellular damage to be repaired. • Amount of tissue radiated: • Total body irradiation produces more adverse effects than if small, localized areas of the body are exposed. • Cell sensitivity • Age

18. Factors Affecting Radiation Injury • Cell sensitivity: • More damage occurs in cells that are rapidly dividing. • Age: • Children are more susceptible to radiation damage than adults.

19. Short Term and Long Term Effects: • Short Term Effects: high doses of radiation over short periods of time tend to kill cells. • Death • Skin burns (erythemia), peeling, blistering • Hair loss • Sterility • Cataracts • Long Term Effects: low doses of radiation over extended period of time produce chronic, or long-term effects, which may not be observed for many years.

20. Somatic and Genetic Effects: • Somatic Effects: • Occur in all cells of the body except the reproductive cells. • These changes are not passed along to future generations. • They only affect the individual exposed. • Primary consequence is cancer www.ehow.com/video_49847#25537E

21. Somatic and Genetic Effects • Genetic Effects: • Occur in reproductive cells • Are passed along to future generations • These changes do not affect the exposed individual, but are passed along by mutations in offspring. • Genetic damage cannot be repaired

22. Somatic VS Genetic Effects of Radiation

23. Tissue & Organ Sensitivity • Tissues and organs vary with their sensitivity to radiation. • Radiosensitive organs include: • Lymphoid tissue (small lymphocyte) • Bone marrow (blood forming tissue) • Testes • Intestines • Radioresistant organs include: • Salivary glands • Kidney • liver

24. Critical Organs • A critical organ is an organ that, if damaged, would diminish the quality of a person’s life. • In dentistry, some tissues and organs are designated as critical because they are exposed to more radiation than others during dental radiographic procedures.

25. Critical Organs • The critical organs exposed during dental radiographic procedures include: • Skin • Thyroid gland • Lens of the eye • Bone marrow (aka: blood forming tissue) • Turn to page 41 of your text

26. Critical Organs Panoramic X-ray Exposure Bite-wing X-ray Exposure

27. Radiation Measurement • Currently 2 systems are used • Traditional/Standard System • Roentgen (R) • Radiation absorbed Dose (rad) • Roentgen equivalent (in) man (rem) • SI System • Coulombs/kilogram (C/kg) • Gray (Gy) • Sievert (Sv)

28. Exposure Measurement - R • Roentgen (R)- • This is the traditional unit of exposure. • That is the amount of ionization created in a given volume of air.

29. Dose Measurement - RAD • Radiation absorbed dose (rad) • This is the traditional unit of dose • Dose can be defined as the amount of energy absorbed by a tissue.

30. Dose Equivalent Measure - REM • Different types of radiation have different effects on tissue. • The dose equivalent measurement is used to compare the biological effects of different types of radiation • In the traditional system, the unit of dose equivalent is roentgen equivalent (in) man or rem.

31. Sources of Radiation • Radiation can come from 2 sources: • Natural Background Radiation: this radiation comes from the sun, earth, and atmosphere • Artificial Radiation: (man-made) medical/dental x-rays, nuclear, consumer products

32. Sources of Radiation

33. Sources of Radiation

34. Sources of Radiation

35. Consumer Products Smoke detectors that use “americium”-241 Lawn fertilizer containing potassium-40 Cigarettes Gas lanterns Exit signs Natural gas appliances Brick or stone houses Color television sets

36. Fukashima Nuclear Disaster www.youtube.com/watch?v=#2553F2

37. Risk vs. Benefit Principle • Radiation is harmful to living tissue. • Because biological damage results from x-ray exposure, dental radiographs should be prescribed ONLY WHEN the benefit of disease detection outweighs the risk of biologic damage. • When dental x-rays are properly prescribed and exposed, the benefit far outweighs the risk.

38. Pro and Cons of Dental Radiation • Pros • Can help to detect: • Caries • Cysts • Tooth abscess/infection • Retained Roots/Foreign Bodies • Periodontal Disease • Foreign Bodies • Growth Irregularities • Tooth Development • Tooth impactions • Cons • Tissues that can be effected by radiation: • Embryonic tissue • Blood and bone marrow • Skin • Connective tissue • Nerve • Brain • Muscle cells • Enamel

39. Guidelines for Radiation Exposure for Dental Patients • The ADA sets guidelines for how frequently patients should have radiographs taken based on many factors. • We will discuss these in the next section of this course on “Radiation Protection”.