1

Radiological Science in the Context of Radiological Science in the Context of Radiological TerrorismRadiological Terrorism

Basics of Basics of Ionizing RadiationIonizing Radiation

EffectsEffectsCharles R. GeardCharles R. Geard

Center for Radiological ResearchCenter for Radiological ResearchColumbia UniversityColumbia University

2

Radiation and LifeRadiation and Life

In the context of this conference In the context of this conference αα--particles are important only when particles are important only when radioactive material is inhaled or radioactive material is inhaled or ingested.ingested.ββ--rays rays –– only when ingested or skinonly when ingested or skinXX-- and and γγ--rays rays –– external radiationexternal radiationNeutrons Neutrons –– nuclear explosionnuclear explosion

Quantities and UnitsQuantities and Units

Dose Dose –– Measured Physical QuantityMeasured Physical QuantityOld unit Old unit –– radradNew unit New unit –– Gray (Gy)Gray (Gy)

1 Gy = 100 1 Gy = 100 radrad

3

Quantities and UnitsQuantities and Units

Equivalent Dose Equivalent Dose –– Calculated QuantityCalculated QuantityThe same dose of different radiations does The same dose of different radiations does not produce the same biological effect.not produce the same biological effect.Equivalent dose = Equivalent dose = dosedose x radiation weighting x radiation weighting factor (Wfactor (WRR).).WWRR = 20 for = 20 for αα--particles and some neutrons.particles and some neutrons.Old unit Old unit –– remremNew unit New unit –– SievertSievert ((SvSv))

1 1 SvSv = 100 = 100 remrem

Quantities and UnitsQuantities and Units

Effective Dose Effective Dose –– Calculated QuantityCalculated QuantityDifferent organs vary in Different organs vary in radiosensitivityradiosensitivity; ; e.g., thyroid, breast and colon are more e.g., thyroid, breast and colon are more sensitive than extremities.sensitive than extremities.Old unit Old unit –– remremNew unit New unit –– SievertSievert ((SvSv))

1 1 SvSv = 100 = 100 remrem

4

Doses to theDoses to theU.S. PopulationU.S. Population

Exposure to Exposure to Natural RadiationNatural Radiation

5

Radiation Radiation Exposure Due Exposure Due

to Human to Human ActivityActivity

Average Effective Dose in U.S. (3.6 Average Effective Dose in U.S. (3.6 mSvmSv/yr)/yr)

6

Ionizing Ionizing Radiation(sRadiation(s))

Able to ionize atoms Able to ionize atoms –– i.e., knock an i.e., knock an electron out of orbit.electron out of orbit.Able to break chemical bonds and Able to break chemical bonds and disrupt the large molecules that living disrupt the large molecules that living things are made of.things are made of.

Ionizing RadiationIonizing Radiation

The biological effect results, not from The biological effect results, not from the total energy absorbed, but from the total energy absorbed, but from the energy of the individual charged the energy of the individual charged particle or photons of particle or photons of γγ--rays.rays.

7

Total Body IrradiationTotal Body Irradiation

Mass = 70 Mass = 70 kgmkgm..

LD/50/60 = 4 Gy.LD/50/60 = 4 Gy.

Energy absorbed =Energy absorbed =70 x 4 = 280 Joules70 x 4 = 280 Joules

== 280280 = 67 calories= 67 calories..4.184.18

Drinking Hot CoffeeDrinking Hot Coffee

Excess temperature (Excess temperature (°°C) = 60C) = 60°° -- 3737°° = 23= 23°°

Volume of coffee consumed to equal the Volume of coffee consumed to equal the energy in the LD/50/60energy in the LD/50/60 == 6767 == 3 ml3 ml == 1 sip1 sip

2323

8

Chain of EventsChain of Events

incident xincident x--ray photonray photon 1010--1515 secsecTime Scale

↓ fast electron

↓ ↓ion radical 10-5 sec

↓ chemical changes due to the breakage of bonds ↓

↓ days, years orbiological effects generations

RADIATION BIODOSIMETRYDose Predictive Assays

How much radiation has a person/cell received?

Center for High-Throughput Minimally-Invasive Radiation Biodosimetry

Home Land Security – Dirty Bombs!

Rad

iatio

n D

ose

Biological Response

9

BIOLOGICAL RESPONSES TO IONIZING RADIATION

Gene Mutation

Chromosomal Aberrations

Micronuclei

Cell Death

Apoptosis

Changes in Levels of Specific Gene Products

Others………

DNA Damage!

Direct and Indirect ActionDirect and Indirect Action

10

DNA DNA ––

Double Double Strand Strand BreakBreak

Biological Effects of RadiationBiological Effects of Radiation

Cell Killing Cell Killing –– division of damaged division of damaged chromosomeschromosomes–– Relevant to radiotherapy.Relevant to radiotherapy.–– Cause of some effects on the embryo & fetus at Cause of some effects on the embryo & fetus at

low doses, and to adults at high doses.low doses, and to adults at high doses.Mutation in Germ Cells Mutation in Germ Cells -- altered altered chromosomeschromosomes–– Hereditary consequences expressed in later Hereditary consequences expressed in later

generations.generations.Carcinogenesis or Carcinogenesis or LeukemogenesisLeukemogenesis–– Chromosomal changes and/or mutations in Chromosomal changes and/or mutations in

dividing somatic cells.dividing somatic cells.

11

Cell Killing Cell Killing

Conventional RadiologyConventional Radiology–– Doses too small to cause discernible Doses too small to cause discernible

cell killing (<10 cell killing (<10 cGycGy).).Radiological eventRadiological event–– Doses sufficient to cause Doses sufficient to cause erythemaerythema and and

possibly necrosis need to be greater possibly necrosis need to be greater than 1 than 1 GyGy (e.g. an atomic bomb).(e.g. an atomic bomb).

Cellular consequences of radiation exposureCellular consequences of radiation exposure

Cell Death • Apoptosis or necrosis

Cell cycle arrest (cells stop dividing)• Temporary or permanent• Changes in gene products

DNA repair-No changeAlterations-Viable or lethal

12

Damaged Chromosome Reproduction ErrorsDamaged Chromosome Reproduction Errors

DicentricDicentric Chromosome in a Peripheral LymphocyteChromosome in a Peripheral Lymphocyte

13

Chromosome Translocation in Chronic Myeloid LeukemiaChromosome Translocation in Chronic Myeloid Leukemia

14

Complex inter-chromosomal translocation

multiplex FISH

FITC SPECTRUM O TEXAS RED Cy5 DEAC

Combined

15

Radiation and Cell DamageRadiation and Cell Damage

Radiation breaks chromosomes.Radiation breaks chromosomes.DNA breaks repair or DNA breaks repair or mismis--repair.repair.MisMis--repaired chromosomes can lead to repaired chromosomes can lead to abnormal cell division abnormal cell division Cells die and are removed when they attempt to Cells die and are removed when they attempt to divide divide –– micronuclei and micronuclei and nucleoplasmicnucleoplasmic bridgesbridgesCarcinogenic change only expresses in dividing Carcinogenic change only expresses in dividing cells cells –– translocations and small deletionstranslocations and small deletionsUntil then cells are present and can function.Until then cells are present and can function.

Larger the Dose – Greater the Biological Response

Dose Response

Rad

iatio

n D

ose

Biological Response

16

• Separate lymphocytes from whole blood• Split culture: process for micronucleatedcells, DNA damage foci, gene expression• Harvest RNA after 24 hours,

compare on microarray• Follow-up of induced genes

• ALL ENDPOINTS• Reproducibility in multiple donors• Time-course of response• Dose-response relationship

Radiation Radiation BiodosimetryBiodosimetryIrradiation of human peripheral blood Irradiation of human peripheral blood

lymphocyteslymphocytes

17

Aberrations per CellAberrations per Cell

Based on DNA Damage

18

γγ--H2AX fociH2AX foci

γ-H

2AX

foci

per

cel

lγ-

H2A

X fo

ci p

er c

ell

• Radiation causes gene expression changes• Gene expression changes underlie many

cellular responses• We can now study changes in gene

expression across the whole genome• Gene expression profiles may soon

provide useful information for biodosimetry

19

ceramide

MAPK (p38, JNK)

c-Abl

ionizing radiation

cell surface

cytokines and bystander signals

caspasesPKC NFκB

activation

cytokine receptors

plasma membrane

DNAp53ATMDNA-PK

DNA damage

nucleusionizing radiation

Stress Signaling PathwaysStress Signaling Pathways

Protein modifications

Gene expression changes

(Functional Genomics)

Altered cellularfunction

Rel

ativ

e Ex

pres

sion DDB2

CDKN1A

XPC

24 hours post-irradiation

48 hourspost-irradiation

Amundson et al., (2000) Radiation Research, 154 (3): 342-346

Gene induction in PBL persists at least two daysGene induction in PBL persists at least two days

0

2

4

6

8

0 50 100 150 200Dose (cGy)

0

2

4

6

8

0 50 100 150 200Dose (cGy)

DDB2

CDKN1A

XPC

20

Informatic Analysis

Compare ProfileTo Database

Dose Assessment - triage

Blood sample

Developing gene expression for Developing gene expression for biodosimetrybiodosimetry

Array Profile

Integrated profiling cassette

DNA based fociDNA based fociChromosomal domain alterationsChromosomal domain alterations

Micronuclei and Micronuclei and nucleoplasmicnucleoplasmic bridgesbridgesChromosomal Chromosomal aberrationsaberrations

Requirements: Requirements: Speed Accuracy LongevitySpeed Accuracy Longevity

Radiation Radiation biodosimetrybiodosimetryin the event of population radiation exposurein the event of population radiation exposure..

DNA damage and DNA damage and cytogeneticcytogenetic assaysassays

21