BIODOSIMETRY AVAILABLE METHODS AND ROLE IN .ppt

1、BIODOSIMETRY AVAILABLE METHODS AND ROLE IN DOSE ASSESMENT AND PROGNOSIS,Module X,Module Medical X.,- 2,Accidental dosimetry,PHYSICAL DOSIMETRY,BIOLOGICAL DOSIMETRY,CLINICAL DOSIMETRY,DOSE RECONSTRUCTION, Personal Dosimeters,CYTOGENETIC DOSIMETRY Dicentrics, FISH, PCC, MNA,NAUSEA, VOMITING, BLOOD CEL

2、LS COUNTS, SKIN REACTIONS.,OTHER BIOINDICATORS,Module Medical X.,- 3,Physical dosimetry,Module Medical X.,- 4,Clinical dosimetry,Crude estimate of absorbed dose obtainable from clinical presentation,VomitingOnset: 2 h after exposure or later Onset: 1-2 h after exposure or later Onset: earlier than 1

3、 h after exposure Onset: Earlier than 30 min after exposure,MILD ARS (1-2 Gy),MODERATE ARS(2-4 Gy),SEVERE ARS (4-6 Gy),VERY SEVERE ARS (6-8 Gy),Module Medical X.,- 5,Clinical dosimetry using early changes in lymphocyte counts,Module Medical X.,- 6,Clinical dosimetry using granulocyte counts,Module M

4、edical X.,- 7,Cytogenetic dosimetry,Analysis of chromosomal aberrations in peripheral blood lymphocytes - widely used biological dosimetry method for assessing radiation dose, especially useful in persons not wearing dosimeters while exposed to radiationin cases of claims for compensation for radiat

5、ion injuries not supported by unequivocal dosimetric evidencefor validation of occupational radioprotection cases involving suspected low-dose exposures,Module Medical X.,- 8,Biophysical background to chromosome damage,*,High LET,* * * * * * * * *,Low LET,Module Medical X.,- 9,DNA damage,Module Medi

6、cal X.,- 10,Chromosomal structure,Module Medical X.,- 11,Human lymphocytes,LYMPHOCYTES,Dose assessment predominantly based on data obtained from lymphocytesEasily obtained in large quantities from peripheral bloodVast majority of peripheral lymphocytes reside in Go phase of e cell cyclePhytohaemaggl

7、utinin (PHA) converts resting lymphocytes into dividing cells allowing visualization of possible DNA lesions in methaphase chromosomes,Module Medical X.,- 12,Human karyotype,Module Medical X.,- 13,Classification of chromosomal aberrations,Inversion,Symmetrical (STABLE),Breaks,Intrachange,Asymmetrica

8、l (UNSTABLE),Centric Ring,Interchange,Translocation,Dicentric,Module Medical X.,- 14,Biological dose assessment using standard dicentric analysis,Introduced by M. Bender in 1964Isolated lymphocytes stimulated by phytohaemagglutin (PHA) into mitosisArrest of metaphase using colchicineScoring of dicen

9、tric chromosome aberrations in metaphase spreads,Module Medical X.,- 15,Dicentric chromosome aberrations in metaphase spreads,dic,dic,f,f,f,f,Module Medical X.,- 16,Dose response curves,Y = A+aD + bD2,Module Medical X.,- 17,Relationship between RBE and LET,LET (keV/m),RBE,Module Medical X.,- 18,Cali

10、bration curves,Module Medical X.,- 19,Gamma rays, X-rays acute exposure (Low LET),Gamma rays X-rays chronic exposure (Low LET), particles Fast neutrons (High LET),Dose,Dicentric yield,Y = c + aD + bD2,Y = c + aD,Y = c + aD,Dose estimation of acute vs chronic exposure,Effect,Module Medical X.,- 20,Me

11、thods for estimating radiation doses in partial body exposure: Sasaki-method,Module Medical X.,- 21,Dicentric assay,Most accurate method for dose estimation with sensitivity threshold of about 0.1 Gy for whole body low LET radiationEspecially usefulin cases where dosimeter not used, e.g. radiation a

12、ccidentto support physical dosimetry results in radiation protection and safety practiceto determine partial body exposure not detected by locally placed dosimeter,Module Medical X.,- 22,Limitations of dicentric analysis for dose estimation,Dicentrics are unstable and lymphocytes carrying aberration

13、 elimininated with time (average lifetime 150-220 days, depending on dose), hence can underestimate magnitude of doseMethod useful only within few months of irradiation,Module Medical X.,- 23,Translocation assay,In retrospective dosimetry and chronic exposure reciprocal translocations used for dose

14、assessment Translocations considered stable in cell division so yield should not fall with time Typically detected using specific whole chromosome DNA hybridization probes and FISH methodology,Module Medical X.,- 24,Stable chromosome aberration analysis with G-banding,A normal G banded male karyotyp

15、e,An idiogram showing the banding patterns of individual chromosomes by fluorescent and Giemsa staining,Module Medical X.,- 25,Stable chromosome aberration analysis with FISH,Translocation,Deletion,Module Medical X.,- 26,Painting chromosomes Pancentromeric and telomeric probes,Module Medical X.,- 27

16、,Applicability of stable chromosome aberration analysis for biological dosimetry,Method based on scoring stable chromosome aberrations (translocations and insertions) detected with fluorescent in-situ hybridization of whole chromosomesRequires complex procedures and technical equipmentMay be use dec

17、ades after exposureSensitivity threshold a few cGy but method not feasible for doses less than 0.2 Gy because of expense and time needed for analysisSpontaneous level of stable chromosome aberrations not well established,Module Medical X.,- 28,Premature chromosome condensation (PCC) assay,Initially

18、introduced by Johnson and Rao (1970) Mitotic-inducer cells (i.e. CHO) isolated using chemical (colcemid) and physical (rapid shaking of flask) technique Test cells (i.e. human lymphocytes) fused with CHO cells using polyethylene glycol (PEG) Interphase DNA of test cells condense into chromatid/chrom

19、osome-like structures (46 for non-irradiated human cells),Module Medical X.,- 29,PCC technique,PERIPHERAL BLOOD,FICOL SEPARATION,FUSE IN PEG,LYMPHOCYTES,CHO,CHINESE HAMSTER OVARY (CHO) CELLS(Grown in BrdU)COLCEMIDMITOTIC SHAKE OFF (METAPHASE CELLS),PCC,Incubate 1 h (Medium+PHA+Colcemid),Module Medic

20、al X.,- 30,Evaluation criteria for scoring PCCs,Module Medical X.,- 31,PCCs and FISH,Irradiated cells withexcess break,Unirradiated control,Module Medical X.,- 32,Estimation of irradiated body fractions,Module Medical X.,- 33,Applicability of PCC assay for biological dosimetry,Dose estimates obtaina

21、ble within 48 hours of receipt of blood in laboratory Radiation induced mitotic delay does not interfere with assay since performed on interphase nuclei and does not require cell division Method envisioned applicable after partial-body/supra-lethal exposure & improves detection level of lower doses,

22、Module Medical X.,- 34,Micronucleus (MN) assay,Cytochalasin B,Module Medical X.,- 35,MN and nucleoplasmic bridges in binucleated cells (Giemsa stained),A,B,Module Medical X.,- 36,MN assay with pancentromeric probe,A,B,centromere negative,centromere positive,Module Medical X.,- 37,Application of MN a

23、ssay for biological dosimetry,Micronuclei not specific to radiation exposure Discrimination between total and partial body exposure more difficult High doses of radiation interfere with cell division High baseline frequency and age dependency make reliability of assay questionable,Module Medical X.,

24、- 38,Glycophorin A (GPA) somatic cell mutation assay,Performed by two-color immunofluorescence flow cytometry on peripheral blood erythrocytesBased of measuring N/0 variants of erythrocytes, which display phenotype consistent with loss of expression of GPA (M) alleleCan be performed only on individu

25、als heterozygous at this locus that codes for the N/M blood group antigens (approximately half of population)Prompt but requires complex and expensive equipmentSensitivity threshold about 0.2-0.25 Gy,Module Medical X.,- 39,Application of GPA assay for biological dosimetry,Relationship between glycop

26、horin A mutant frequency in red blood cells and radiation dose for about 1200 A-bomb survivors,Module Medical X.,- 40,Biophysical assays - ESR (electron spin resonance),Persistent free radicals formed in solid matrix biomaterial (e.g. dental enamel, nail clippings, hair) from accidentally exposed vi

27、ctim can be detected via ESR Measurements provide reliable biophysical dose estimates & partial body exposure information In some circumstances, certain clothing material, particularly hard plastics and buttons, may be measured and absorbed dose estimated,Module Medical X.,- 41,Characterization of b

28、iological dosimetry methods,Module Medical X.,- 42,Review points,In radiation accidents, important to estimate the absorbed doses in victims to plan appropriate medical treatment In most accidents, physical dosimetry of absorbed dose is not possible. Even where possible, important to confirm the estimates by other methods Most commonly used method cytogenetic analysis of chromosomal aberration in peripheral blood lymphocytes using dicentrics, translocations, PCC and micronuclei assays,