Biological Effects of Ionizing RadiationBiological Effects of Ionizing RadiationDeterministic effectsDeterministic effects

Deterministic effects: overviewDeterministic effects: overviewLectureLecture

IAEA Post Graduate Educational Course Radiation Protection and Safe Use of Radiation Sources

IAEA Post Graduate Educational Course in Radiation Protection and Safety of Radiation Sources

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IntroductionIntroduction Types of health effects of radiation:Types of health effects of radiation:

DeterministicDeterministic StochasticStochastic

Data on deterministic health effects Data on deterministic health effects ere collected from observation of:ere collected from observation of: the side effects of radiotherapythe side effects of radiotherapy the effects on the early radiologiststhe effects on the early radiologists the effects amongst survivors of the atomic the effects amongst survivors of the atomic

bombs at Hiroshima and Nagasaki in Japanbombs at Hiroshima and Nagasaki in Japan the consequences of severe accidents.the consequences of severe accidents.

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ContentContent EEffects of radiation on humanffects of radiation on human Deterministic health effects: definition, Deterministic health effects: definition,

description, examples, time of occurrence, description, examples, time of occurrence, threshold of occurrencethreshold of occurrence

General dose-response curveGeneral dose-response curve Variation in person’s sensitivityVariation in person’s sensitivity Acute and chronic damage of the tissue due to Acute and chronic damage of the tissue due to

ionizing radiationionizing radiation Influencing factors on person’s radiation Influencing factors on person’s radiation

sensitivitysensitivity Influence of dose rateInfluence of dose rate

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OverviewOverview Deterministic health effects: Deterministic health effects:

Mechanism of developmentMechanism of development Typical featuresTypical features

Examples of deterministic health effects:Examples of deterministic health effects: Acute radiation syndromeAcute radiation syndrome Skin burnsSkin burns SterilitySterility HypothyroidismHypothyroidism CataractCataract

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Radiation Causes Ionisation Of:Radiation Causes Ionisation Of:ATOMSATOMS

which will affectwhich will affectMOLECULESMOLECULES

which may affectwhich may affectCELLSCELLS

which may affectwhich may affectTISSUESTISSUES

which may affectwhich may affectORGANSORGANS

which may affectwhich may affectTHE WHOLE BODYTHE WHOLE BODY

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Ionising Radiation and HumanIonising Radiation and HumanCellular LevelCellular Level

Normal repair of damage

Daughter cells die

Cell dies from damage

No repair or non-identicalrepair before reproduction

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Deterministic Health Effects: Deterministic Health Effects: DefinitionDefinition A radiation effect for which generally a A radiation effect for which generally a

threshold level of dose exists above which threshold level of dose exists above which the severity of the effect is greater for a the severity of the effect is greater for a higher dose.higher dose. The level of the threshold dose is The level of the threshold dose is

characteristic of the particular health effect but characteristic of the particular health effect but may also depend, to a limited extent, on the may also depend, to a limited extent, on the exposed individual. exposed individual.

The term non-stochastic effect is used in some The term non-stochastic effect is used in some older publications, but is now superseded older publications, but is now superseded

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Deterministic Health EffectsDeterministic Health Effects A cell that has been hit A cell that has been hit

may destroy itself or may may destroy itself or may be destroyed while be destroyed while dividing dividing

Cell killing is not equal to Cell killing is not equal to health effecthealth effect

Only massive cell killing Only massive cell killing leads to health effectsleads to health effects

Massive cell killing can Massive cell killing can occur only after high occur only after high dosesdoses

These are called These are called deterministic effectsdeterministic effects

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Deterministic Health EffectsDeterministic Health Effects (Cont’d)(Cont’d) Early appearance Early appearance

(days to weeks, excl. (days to weeks, excl. cataract)cataract)

Existence of dose Existence of dose threshold, specific for threshold, specific for particular effectparticular effect

Below dose thresholds Below dose thresholds - no effect - no effect

Above threshold the Above threshold the severity depends on severity depends on level of radiation doselevel of radiation dose

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Deterministic Health EffectsDeterministic Health Effects (Cont’d)(Cont’d) Some deterministic effects have Some deterministic effects have

characteristics that distinguish them characteristics that distinguish them from similar effects due to other from similar effects due to other causes, which may help to identify the causes, which may help to identify the affected individualsaffected individuals

The occurrence of the initial event has The occurrence of the initial event has sometimes been detected by the sometimes been detected by the unexpected appearance of unexpected appearance of deterministic effectsdeterministic effects

Need specialized treatmentNeed specialized treatment

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Typical dose effect relationships Typical dose effect relationships for deterministic effects expressed for deterministic effects expressed in a populationin a population

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Dose-effect RelationshipsDose-effect Relationships: : variation in person’s sensitivityvariation in person’s sensitivity

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Deterministic Health Effects: time Deterministic Health Effects: time of occurrence:of occurrence: Deterministic health effects could occur:Deterministic health effects could occur:

Hours-weeks after exposure Hours-weeks after exposure ARS, skin burns, sterility

Months-years after exposureMonths-years after exposure Cataract

Occurrence is connected with radiation Occurrence is connected with radiation damage of the tissue:damage of the tissue: AcuteAcute ChronicChronic

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Acute damage of the tissueAcute damage of the tissue OOccurs early, within days or weeks after ccurs early, within days or weeks after

radiation exposureradiation exposure The main clinical sign – inflammationThe main clinical sign – inflammation The main structural feature – hypoplasiaThe main structural feature – hypoplasia Latency depends on cell turnover kinetics of Latency depends on cell turnover kinetics of

the tissue the tissue Spontaneous recovery occurs from surviving Spontaneous recovery occurs from surviving

stem cellsstem cells Severity can be most effectively reduced by Severity can be most effectively reduced by

increased dose protractionincreased dose protraction

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Chronic damage of the tissueChronic damage of the tissue OOccurs late, after many months and ccurs late, after many months and

may be progressive over yearsmay be progressive over years The main clinical sign – fibrosisThe main clinical sign – fibrosis The main structural feature – atrophyThe main structural feature – atrophy No fixed latency but continuous No fixed latency but continuous

progression, no recoveryprogression, no recovery Severity is most effectively reduced Severity is most effectively reduced

by decrease of dose per fractionby decrease of dose per fraction

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Deterministic Health EffectsDeterministic Health Effects::Threshold of OccurrenceThreshold of Occurrence

Organ or Organ or tissuetissue

Dose in Dose in less thanless than 2 2 daysdays, , GyGy

Deterministic effectsDeterministic effects

Type of effectType of effect Time of Time of occurrenceoccurrence

Whole body Whole body (bone marrow)(bone marrow) 11 DeathDeath 1 – 2 months1 – 2 months

SkinSkin 33 ErythemaErythema 1 – 3 weeks1 – 3 weeks

ThyroidThyroid 55 HypothyroidismHypothyroidism 1st – several 1st – several yearsyears

Lens of the Lens of the eyeeye 22 CataractCataract 6 months - 6 months -

several yearsseveral years

GonadsGonads 33 Permanent Permanent sterilitysterility weeksweeks

FoetusFoetus 0.10.1 TeratogenesisTeratogenesis --

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Acute Radiation SyndromeAcute Radiation Syndrome Most notable deterministic health effect of Most notable deterministic health effect of

ionizing exposureionizing exposure Signs and symptoms are not specific for Signs and symptoms are not specific for

radiation injury but collectively highly radiation injury but collectively highly characteristic for ARScharacteristic for ARS

Combination of symptoms occurring hours Combination of symptoms occurring hours to week after exposureto week after exposure

Extent and severity of symptoms are Extent and severity of symptoms are determined by:determined by: Total radiation dose receivedTotal radiation dose received Dose rateDose rate Exposed part of the body (whole body or local Exposed part of the body (whole body or local

irradiation)irradiation)

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Influencing factors on radiation Influencing factors on radiation sensitivitysensitivity

The sensitivity to radiation of different The sensitivity to radiation of different organs and their consequences for the organs and their consequences for the individual person vary very much between individual person vary very much between organsorgans

It depends on: It depends on: the fraction of the organ irradiated (the volume the fraction of the organ irradiated (the volume

effect)effect) the overall exposure time (the time factor)the overall exposure time (the time factor) the dose rate or dose per fraction (the the dose rate or dose per fraction (the

fractionation effect)fractionation effect)

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Influence of dose rateInfluence of dose rate

When the radiation dose rate is When the radiation dose rate is reduced from about 1 Gy/min to 0.3 reduced from about 1 Gy/min to 0.3 Gy/h there is a reduction in the cell Gy/h there is a reduction in the cell killing from a given dose killing from a given dose

As the dose rate is reduced, the As the dose rate is reduced, the slope of the survival curve becomes slope of the survival curve becomes shallowershallower

In some cell lines an In some cell lines an ininvverseerse dose- dose-rate effect is evident rate effect is evident

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SummarySummary

This lecture presented overview of deterministic This lecture presented overview of deterministic health effectshealth effects

The following topics were covered in the lecture: The following topics were covered in the lecture: effects of radiation on human, deterministic health effects of radiation on human, deterministic health effects: definition, description, examples, time of effects: definition, description, examples, time of occurrence, threshold of occurrence, general occurrence, threshold of occurrence, general dose-response curve, variation in person’s dose-response curve, variation in person’s sensitivity, acute and chronic damage of the tissue sensitivity, acute and chronic damage of the tissue due to ionizing radiation, influencing factors on due to ionizing radiation, influencing factors on person’s radiation sensitivity, influence of dose person’s radiation sensitivity, influence of dose raterate

Comments are welcomedComments are welcomed

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Where to Get More InformationWhere to Get More Information

UNSCEAR, Sources and Effects of UNSCEAR, Sources and Effects of Ionizing Radiation, 2000 Report to the Ionizing Radiation, 2000 Report to the General Assembly with Scientific General Assembly with Scientific Annexes, United Nations, New York Annexes, United Nations, New York (2000)(2000)

Lectures describing specific examples of Lectures describing specific examples of deterministic health effectsdeterministic health effects