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RADIATION BIOLOGY

RADIATION BIOLOGY. Christos Angelopoulos, DDS, MS. Radiation Biology is the study of the effects of ionizing radiations on living tissues. BIOLOGIC EFFECTS OF RADIATION. DNA, RNA, ADP, ATP, NAD, cytochrome oxidase, glucokinase, proteins and many more. Injury to the chemicals of life.

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RADIATION BIOLOGY

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  1. RADIATION BIOLOGY Christos Angelopoulos, DDS, MS

  2. Radiation Biology is the study of the effects of ionizing radiations on living tissues

  3. BIOLOGIC EFFECTS OF RADIATION DNA, RNA, ADP, ATP, NAD, cytochrome oxidase, glucokinase, proteins and many more Injury to the chemicals of life Direct effects Indirect effects

  4. BIOLOGIC EFFECTS OF RADIATION The very first interaction between the ionizing radiation and matter occurs at subatomic level (electrons) within the first 10-13 sec. Excitation Ionization Breaking of molecular bonds

  5. DIRECT EFFECTS OF RADIATION When the energy of the ionizing radiation is deposited directly in the chemicals of life: DNA, RNA, proteins, enzymes, etc. Approximately 1/3 of the biologic effects of x-ray exposure result from direct effects

  6. INDIRECT EFFECTS OF RADIATION When the energy of the ionizing radiation is deposited on water molecules first, causing the formation of free radicals, and then the free radicals act upon the biologic macromolecules (chemicals of life) Approximately 2/3 of the biologic effects of x-ray exposure result from indirect effects due to the abundance of water in the living tissues

  7. RADIOLYSIS OF WATER Free radicals:molecules that result from the irradiation of water, containing an unpaired electron and very active chemically H2O H2O H* H2O H2O H2O O* H2O HO2* H+ H2O H2O HO- H* H2O H2O H2O H2O O- O- HO2* H2O2 HO* H2O H2O H2O

  8. THE TARGET THEORY Strand breakage HO2* Change or loss of a base Hydrogen bond breakage HO2* HO2* HO* Cross-linking HO2* HO*

  9. RADIATION EFFECTS AT CELLULAR LEVEL

  10. Chromosome aberration * THE CELL CYCLE G1 S M G2 * *

  11. Chromatid aberration G1 S M G2 *

  12. CELL SURVIVAL CURVES Survived cells Radioresistant Radiosensitive Radiation dose

  13. RADIOSENSITIVITY & CELL TYPE BERGONIE &TRIBONDEAU (1906): The higher the mitotic rate of a cell, the more radiosensitive it is The more primitive (undifferentiated) a cell, the more radiosensitive it is* *Except oocytes & lymphocytes

  14. RADIOSENSITIVITY & CELL TYPE RADIOSENSITIVE CELLS RADIORESISTANT CELLS • Germinal cells of ovary • Seminiferous epithelium of testes • Lymphocytes • Erythrocytes • Myeloblasts • Epithelium (skin,intestines) • Connective tissue cells • Glandular cells • Kidney tubule cells • Bone cells • Brain cells • Nerve cells • Muscle cells

  15. RADIATION EFFECTS ON TISSUES & ORGANS HIGH SENSITIVITY Small lymphocyte Bone marrow Reproductive cells Intestinal mucosa

  16. RADIATION EFFECTS ON TISSUES & ORGANS FAIRLY HIGH SENSITIVITY Skin Lens of the eye Oral mucosa

  17. RADIATION EFFECTS ON TISSUES & ORGANS MEDIUM SENSITIVITY Connective tissue Small blood vessels Growing bone, cartilage

  18. RADIATION EFFECTS ON TISSUES & ORGANS FAIRLY LOW SENSITIVITY Mature bone, cartilage Salivary glands Thyroid gland Kidney Liver

  19. RADIATION EFFECTS ON TISSUES & ORGANS LOW SENSITIVITY Muscle Nerve

  20. RADIATION EFFECTS ON TISSUES & ORGANS Organs that if damaged by radiation have a greater potential for reducing the quality of life CRITICAL ORGANS Lens of the eye Gonads Fetus Bone marrow Thyroid gland Salivary glands Skin Bone

  21. RADIATION EFFECTS ON TISSUES & ORGANS Short-term exposures …direct loss of parenchymal cells Long-term exposures …indirect loss of parenchymal cells due to damage to fine vasculature

  22. RADIATION EFFECTS ON TISSUES & ORGANS Latent period Time interval between irradiation and development of an observed effect Cumulative effects of radiation …multiple exposures to ionizing radiation produce an additive effect…

  23. FACTORS AFFECTING RADIATION INJURY • Type of radiation • Total dose • Acute VS chronic exposure (dose rate) • Whole body VS local exposure • Oxygen effect • Chemical protectors • Host factors (age, sex) • Type of tissue • Phase of cell cycle • Species differences

  24. LETHAL DOSE (LD) 50/30 The radiation dose which will result in death of the 50% of the irradiated population in 30 days Humans 300 rads Monkeys 600 rads Rats 750 rads

  25. LONG-TERM EFFECTS OF RADIATION Tumors Leukemia Cataracts Life span shortening Genetic mutations

  26. RADIATION DOSE-RESPONSE CURVE The graphic relationship between levels of radiation dose and the magnitude of a radiation effect or injury

  27. RADIATION DOSE-RESPONSE CURVES Tissue damage Linear threshold response D Radiation dose

  28. RADIATION DOSE-RESPONSE CURVES Tissue damage Linear non-threshold response Tumors Life span shortening Genetic mutations Radiation dose

  29. RADIATION DOSE-RESPONSE CURVES Tissue damage Linear quadratic response Leukemia Radiation dose

  30. RADIATION DOSE-RESPONSE CURVES Tissue damage Non linear threshold response Cataracts D Radiation dose

  31. RADIATION UNITS & MEASUREMENT Exposure …how much exposure comes out of the x-ray machine …countionizations in the air at the cone of the radiographic machine Roentgen (old system) Exposure unit or Culomb/Kg(SI)

  32. RADIATION UNITS & MEASUREMENT Dose …the amount of x-ray energy absorbed by a unit mass of tissue …exposure DOES NOT equal dose… rad (old system) Gray (Gy)(SI)

  33. RADIATION UNITS & MEASUREMENT Dose equivalent (H) …allows a comparison of biologic effects of different types of ionizing radiation …equal doses of different types of radiation produce different amounts of biologic damage rem (old system) Sievert (Sv)(SI)

  34. RADIATION UNITS & MEASUREMENT Dose equivalent (H) …takes into consideration differences between radiation by using a radiation Quality factor (QF), H=Dose X QF Radiation QF X-rays 1 Gamma rays 1 L.E. protons 5 Alpha 10

  35. RADIATION UNITS & MEASUREMENT H (dose equivalent) = D (dose) X QF … if we want to compare the biological effects of 0.5 Gys of x-rays to 0.5 Gys of alpha particles… H (dose equiv.) x-rays = 0.5 X 1= 0.5 Sv H (dose equiv.) alpha p = 0.5 X 10= 5 Sv Radiation QF X-rays 1 Gamma rays 1 L.E. protons 5 Alpha 10

  36. RADIATION UNITS & MEASUREMENT … if we want to compare the biological damage of 0.5 Gys of x-rays to the (R) hand with 0.5 Gys of x-rays to the breast….or a local exposure VS a whole body exposure OUR UNITS ARE NOT GOOD ENOUGH Effective dose (E) …helps us understand the assessment of biologic consequences (risk) of radiation to a localized part of the body and the degree to which this local exposure would increase a person’s “whole body” risk of developing Ca

  37. EXPOSURE & DOSE IN RADIOGRAPHY Effect that increases in severity as radiation dose increases, after a threshold dose has been reached Deterministic effect The effect whose probability of occurrence rather than its severity is increased with increased dose (no threshold) Stochastic effect

  38. SOURCES OF RADIATION EXPOSURE AVERAGE ANNUAL EFFECTIVE DOSE TO US POPULATION NATURAL (BACKGROUND) 83% Cosmic 8% Terrestrial 8% Internal 67% Radon gas 56% ARTIFICIAL (MEDICAL) 15% Medical x-rays 11% Nuclear Medicine 4% CONSUMER PRODUCTS 2% 3.60 mSv

  39. SOURCES OF RADIATION EXPOSURE VARIATIONS FROM AVERAGE… NATURAL (BACKGROUND) Cosmic 0.27 mSv/yr 0.50 mSv/yr (Colorado) Terrestrial 0.28 mSv/yr 0.90 mSv/yr (Colorado) Internal Radon gas 3.00 mSv 3.85 mSv ARTIFICIAL (MEDICAL) Medical x-rays Nuclear Medicine CONSUMER PRODUCTS 8 mSv daily

  40. EXPOSURE TO CRITICAL ORGANS FROM DENTAL RADIOGRAPHY Increased risk/ tissue damage FMS, round cone, D-speed film Panoramic Lens of the eye 200,000 mrads 60 mrads 8 mrads Bone marrow 5,000 mrads 9-14 mrads 17 mrads Thyroid gland 6,000 mrads 23 mrads 32 mrads Skin 25,000 mrads 1,300 mrads 632 mrads

  41. EXPOSURE FROM INTRAORAL RADIOGRAPHS (D-film) 70 kVp 215-365 mrads/film 75 kVp 200-325 mrads/film 90 kVp 100-200 mrads/film Higher kVp reduces exposure

  42. EXPOSURE FROM INTRAORAL RADIOGRAPHS 70 kVpD-speed film300 mrads/film 70 kVpE-speed film150 mrads/film

  43. EXPOSURES FROM DENTAL RADIOGRAPHS EQUIVALENT NATURAL EXPOSURE EXAM E (mSv) FMS (Round cone-D)150 19 FMS (Rectan. cone-E)33 4 Panoramic26 3.3 CT mandible761-3,324 95-415 Chest80 10 8 mSv daily

  44. THE RISKS FROM DENTAL RADIOGRAPHY CANCER In 2002 almost 1,300,000 new cases of cancer were diagnosed and over 550,000 people died from cancer…

  45. THE RISKS FROM DENTAL RADIOGRAPHY • Latent period • Indistinguishable from other cancers • Insufficient human data at diagnostic doses • Local vs whole body exposures • Single vs multiple exposures • Radiation sensitive populations

  46. THE RISKS FROM DENTAL RADIOGRAPHY ICRP International Commission on radiological Protection Probability co-efficient for developing Ca and hereditary effects from low doses of radiation is: 0.073 ca/Sv

  47. EXPOSURES FROM DENTAL RADIOGRAPHS PROBABILITY OF CANCER/1,000,000 CASES EXAM E (mSv) FMS (Round cone-D)150 11 FMS (Rectan. cone-E)33 2.4 Panoramic26 1.9 CT mandible761-3,324 55-242 Chest80 5.8 8 mSv daily

  48. ONE IN A MILLION RISKS • To smoke 1.4 cigarettes and develop cancer • To drink 30 cans of diet soda and develop cancer • To have a panoramic radiograph and develop cancer

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