Prof. V. Grégoire Dr. P. Smeesters Mr M. Despiegeleer

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2 1. Grandeurs et Unités - Mécanismes biologiques de l action des rayonnements ionisants 2. Effets aigus d une irradiation accidentelle 3. Cancers radio-induits 4. Effets héréditaires radio-induits 5. Effets de l irradiation in utero 6. Législation: les normes de bases; principes de radioprotection opérationnelle 7. Travaux pratiques: emploi de détecteurs en situation de routine; dosimétrie des travailleurs; visites des installations du contrôle physique Prof. V. Grégoire Dr. P. Smeesters Mr M. Despiegeleer

3 Radiobiology for the Radiologist, Eric J. Hall. J.B. Lippincott Company, Philadelphia, recommendations of the International Commission on Radiological Protection, Annals of the ICRP, publication 60, Exposure to ionizing radiations: radiobiological effects and pathogenesis, A. Wambersie et al., Revue Médicale de Bruxelles, 17: et 75-84, 1996 ou Louvain Med., 114: S97-S132,

4 Electromagnetic radiation (low LET): photons, γ-rays, X-rays Particulate Radiation(high LET) - charged particles: electrons, protons, α particles - neutrons - heavy charged ions: carbon, neons, argon, 4

5 E = hν ν = c/λ 5

6 Indirectly ionizing radiation: X-rays, γ-rays, neutrons - photoelectric process: Z 3 - Compton process: higher photon energy - pair production Directly ionizing radiation: charged particles 6

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13 Low LET High LET 13

14 Electrons Photons 14

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16 X- and γ-rays are indirectly ionizing; the first step in their absorption is the production of fast recoil electrons. Neutrons are also indirectly ionizing; the first step in their absorption is the production of fast recoil protons, α-particles, and heavier nuclear fragments. Electrons and other charged particles are directly ionizing; they lost their energy by progressive collision. The shape of the depth-dose curves (and thus the absorption) depends on the type of ionizing radiation and their energy. 16

17 Biological effects of X-rays may be due to the direct or indirect action About two thirds of the biological damage by X-rays is due to indirect action High-LET radiations produce most biological damage by the direct action, which cannot be modified by chemical sensitizers and protectors The physics of the absorption process is over second; the chemistry takes longer; the biology takes days to months for cell killings, years for carcinogenesis, and generations for heritable damage 17

18 Absorbed dose: 1 Gray (Gy) = 1 joule/kg = increase of C per gr water 18

19 Equivalent dose = absorbed dose * radiation weighting factor (W R ) Type and energy range in Sievert (Sv) W R Photons, all energies 1 Electrons, all energies 1 Neutrons, < 10 kev 5 > 10 kev < 100 kev 10 > 100 kev < 2 MeV 20 > 2 MeV < 20 MeV 10 > 20 MeV 5 Protons, > 2 MeV 5 α-particles, fission fragments, heavy nuclei 20 From ICRP 60 19

20 Effective dose = Σ absorbed dose * W R * tissue weighting factor (W T ) in Sievert (Sv) Tissue or organ W T Gonads 0.20 Bone Marrow 0.12 Colon 0.12 Lung 0.12 Stomach 0.12 Bladder 0.05 Breast 0.05 Liver 0.05 Esophagus 0.05 Thyroid 0.05 Skin 0.01 Bone surface 0.01 Remainder 0.05 From ICRP 60 20

21 Committed equivalent dose = equivalent dose over 50 years (70 years for children) Committed effective dose = effective dose over 50 years (70 years for children) 21

22 Collective equivalent dose = equivalent dose * number of persons exposed (in person-sievert) Collective effective dose = effective dose * number of persons exposed (in person-sievert) Collective effective dose commitment = committed effective dose * number of persons exposed (in person-sievert) 22

23 For individuals - absorbed dose - equivalent dose - effective dose - committed equivalent dose - committed effective dose For populations - collective equivalent dose - collective effective dose - collective effective dose commitment 23

24 Cellular processes involved in # cell death after ionizing radiations. Ionizing radiations Ionizations / Excitations Free-radical production Direct effect Cell surface receptor Repair processes Initial genomic damage (DNA / chromosome) Division delay Signal transduction pathways Residual genomic damage (DNA / chromosome) Programmed cell death Clonogenic cell death Tumor shrinkage Loss of normal tissue functional Integrity including carcinogenesis 24

25 Clonogenic cell survival. 25

26 Time-lapse microcinematography 26

27 Clonogenic cell survival. 27

28 Clonogenic cell survival. 28

29 Clonogenic cell survival Surviving fraction SCC 61 SCC 12 B Absorbed dose (Gy) 29 From Schwartz et al.

30 The key function of DNA 30

31 Structure of DNA 31

32 Structure of DNA 32

33 DNA damages 33

34 DNA damages Type of lesion Number per Gray Double strand breaks (dsb) 40 Single strand breaks (ssb) Base damage Sugar damage DNA-DNA crosslinks 30 DNA-protein crosslinks (dpc) 150 Alkali-labile sites

35 0.5 Quantification of DNA damages Fraction of activity released Absorbed dose (Gy) 35

36 DNA Repair 36

37 DNA Repair 37

38 HR and NHEJ Non-homologous end-joining Homologous recombination 3 3 Joint molecule formation Re-ligation Fill-in or deletion, ligation Repair DNA synthesis Resolution of intermediates, ligation 38

39 HR versus NHEJ NHEJ Repairs most DSB - 80% Important for radiosensitivity Error prone All parts of the cell cycle ½ time ~2-4 hours Defects rare in cancer Non-proliferating tissues Early versus late responding tissue HR Repairs fewer DSB 20% Important for radiosensitivity Error free S and G2 phase responsible for change in sensitivity in the cell cycle ½ time long 24hours? Varies more between cell lines (high in stem cells) Defects common in cancer Proliferating tissues 39

40 Quantification of DNA Repair Percent of initial damage BR HF Repair time (min.) 40 From Badie et al.

41 Structure of chromosome 41

42 Chromosome and chromatid aberrations 42

43 Chromosome aberrations 43

44 Quantification of chromosome breaks Chromosome breaks per cell SCC12 B2 SCC Absorbed dose (Gy) 44 From Hittelman et al.

45 Quantification of chromosome dicentrics and rings 45

46 HR and Human Disease Many diseases associated with the sensors and transducers Ataxia Telangiectasia mutations in ATM Patients are radiosensitive Elevated risk of cancer Have several developmental and neural abnormalities AT like disorder mutations in MRE11 Nijmegen breakage syndrome mutations in NBS Familial (inherited) breast cancer - BRCA1, BRCA2 Inherited breast and ovarian cancer Fanconi s Anemia FANCA,B,C,D1,D2,E FANCB,D1=BRCA2 Sensitive to crosslinking agents Increased risk of cancer 46

47 Overview of the cell cycle 47

48 Cell cycle control: G1-S transition 48

49 Tumor suppressor gene: the retinoblastoma example 49

50 Programmed cell death - apoptosis >< necrosis APOPTOSE NECROSE gonflement cellulaire, lésion des organites, altération de la chromatine. lyse cellulaire, destruction des organites, destruction de la chromatine. condensation de la chromatine, diminution du volume cellulaire, changements membranaires. formation des corps apoptotiques chromatine fragmentée, organites intacts. phagocytose inflammation 50

51 Programmed cell death - apoptosis 51

52 Programmed cell death - apoptosis: an active process privation en facteurs stress oxidatif FasL, de croissance perforine radiations ionisantes TNFα granzyme B lésions à l ADN (p53) autres 1 signal 3 exécution Bcl-2, Bcl-xL mitochondrie CrmA p35 ZVAD YVAD DEVD caspases mitochondrie ψm, cytochrome c AIF, radicaux libres Apoptose boucle d autoamplification 2 contrôle point de non retour 52

53 Programmed cell death - apoptosis: DNA fragmentation 53

54 The p53-dependant signaling pathways 54

55 The p53-dependant signaling pathways 55

56 Hypersensitivity syndromes.99 Nl Cumulative frequency AT + + AT + - FA Mean inactivating dose (Gy) 56 Deschavanne & Malaise, 1986

57 Relative Biological Effectiveness (RBE) D high LET D low LET Dose (Gy) Surviving fraction Low LET RBE = D low LET / D high LET High LET 57

58 RBE and LET 58

59 Many single-strand damages are produced in DNA by radiation but are readily and faithfully repaired using the opposite DNA strand as a template. Damages in both strands that are opposite, separated by only a few base pairs, or locally multiple may lead to a double-strand break (dsb). In mammalian cells, double-strand breaks are mainly repaired by nonhomologous end joining (NHEJ). Damages that are not repaired or that are mis-repaired in pre-replication phase (G0-G1 cells) may lead to chromosome aberrations. Damages that are not repaired or that are mis-repaired in post-replication phase (late-s or G2 cells) may lead to chromatid aberrations. 59

60 #Asymetrical exchange aberrations (dicentrics and rings) are mainly lethal. Symetrical exchange aberrations (translocations and deletions) resulting from mis-repaired DNA damages may lead to carcinogenesis. Techniques available to study DNA dsbs are not sensitive enough to be used as biological dosimetry in case of accidental irradiation. Scoring aberrations in lymphocytes from peripheral blood may be used to estimate total-body doses in humans with a sensitivity of 0,25 Gy. Ionizing radiation induce a cell cycle arrest at the G1-S border to prevent damaged DNA to be replicated in S-phase. 60

61 #After exposure to ionizing radiation, cells mainly die from necrosis (clonogenic cell death). Apoptosis is an active form of cell death which is involved in tissue homeostasis after ionizing radiation (e.g. preventing carcinogenesis). Genetic predisposition (e.g. mutations in p53, Rb, or AT gene) may render cells more sensitive to ionizing radiations. Hight LET radiations (e.g. neutrons, α-particles) are much more effective than X-rays or γ-rays (RBE > 1). 61