Dh 111 radiation biology (ch.4) power point

Copyright © 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.Copyright © 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Dental RadiographyDental Radiography

QuestionsQuestions How does radiation damage cells?How does radiation damage cells? What are the differences between short- and long-What are the differences between short- and long-

term effects of radiation damage?term effects of radiation damage? What are the exposure risks of dental radiation?What are the exposure risks of dental radiation?



Chapter 4 reading:Chapter 4 reading: Haring (pp. 38-50)Haring (pp. 38-50)



Chapter 4 outline Chapter 4 outline Radiation BiologyRadiation Biology

Radiation InjuryRadiation Injury Radiation EffectsRadiation Effects Radiation MeasurementsRadiation Measurements Radiation RisksRadiation Risks


IntroductionIntroduction

PurposePurpose To describe the mechanisms and theories of To describe the mechanisms and theories of

radiation injuryradiation injury To define the basic concepts and effects of To define the basic concepts and effects of

radiation exposureradiation exposure To detail radiation measurementsTo detail radiation measurements To discuss the risks of radiation exposureTo discuss the risks of radiation exposure


Radiation InjuryRadiation Injury

Mechanisms of injuryMechanisms of injury Theories of radiation injuryTheories of radiation injury Dose-response curveDose-response curve Stochastic and nonstochastic radiation effectsStochastic and nonstochastic radiation effects Sequence of radiation injurySequence of radiation injury Determining factors for radiation injuryDetermining factors for radiation injury


Mechanisms of InjuryMechanisms of Injury

Haring (p. 39)Haring (p. 39)

Some x-rays do not reach the dental x-ray film; Some x-rays do not reach the dental x-ray film; they are absorbed by the patient’s tissuethey are absorbed by the patient’s tissue Chemical changes occur that result in biologic Chemical changes occur that result in biologic

damagedamage

Two mechanisms of radiation injury are possibleTwo mechanisms of radiation injury are possible IonizationIonization Free radical formationFree radical formation


IonizationIonization

Haring (p. 39) (Fig. 4-1)Haring (p. 39) (Fig. 4-1)

Results when x-rays strike patient tissueResults when x-rays strike patient tissue Produced through the photoelectric effect or Produced through the photoelectric effect or

Compton scatterCompton scatter Results in formation of a positive atom and Results in formation of a positive atom and

dislodged negative electrondislodged negative electron This electron will interact with other atoms within This electron will interact with other atoms within

the absorbing tissues causing chemical changes the absorbing tissues causing chemical changes within the cell that results in biologic damagewithin the cell that results in biologic damage


Free Radical FormationFree Radical Formation

Haring (pp. 39-40) (Figs. 4-2, 4-3)Haring (pp. 39-40) (Figs. 4-2, 4-3)

Cell damage occurs primarily through Cell damage occurs primarily through formation of free radicalsformation of free radicals

Free radicals are formed when an x-ray Free radicals are formed when an x-ray photon ionizes waterphoton ionizes water Free radicalFree radical

• An uncharged atom or molecule that exists with a single, An uncharged atom or molecule that exists with a single, unpaired electron in its outermost shellunpaired electron in its outermost shell

• Highly reactive and unstable Highly reactive and unstable


Theories of Radiation InjuryTheories of Radiation Injury

Haring (p. 40)Haring (p. 40) Damage to living tissue caused by exposure Damage to living tissue caused by exposure

to ionizing radiation may result from to ionizing radiation may result from A direct hit and absorption of an x-ray photon A direct hit and absorption of an x-ray photon

within a cellwithin a cell Absorption of an x-ray photon by water within a Absorption of an x-ray photon by water within a

cell accompanied by free radical formationcell accompanied by free radical formation Two theories to describe how radiation Two theories to describe how radiation

damages biologic tissuesdamages biologic tissues Direct theoryDirect theory Indirect theoryIndirect theory


Direct TheoryDirect Theory

Cell damage results when ionizing radiation Cell damage results when ionizing radiation directly hits critical areas within the celldirectly hits critical areas within the cell Occurs infrequentlyOccurs infrequently


Indirect TheoryIndirect Theory

X-ray photons are absorbed within the cell X-ray photons are absorbed within the cell and cause the formation of toxins, which in and cause the formation of toxins, which in turn damage the cellturn damage the cell When x-ray photons are absorbed by water within When x-ray photons are absorbed by water within

a cell, free radical formation resultsa cell, free radical formation results The free radicals combine to form toxins that The free radicals combine to form toxins that

damage cells damage cells


Dose-Response Curve Dose-Response Curve

Haring (pp. 40-41) (Fig. 4-4)Haring (pp. 40-41) (Fig. 4-4) Used to correlate the damage of tissue with Used to correlate the damage of tissue with

the dose of radiation receivedthe dose of radiation received A linear, nonthreshold relationship is seenA linear, nonthreshold relationship is seen

The linear relationship indicates that the response The linear relationship indicates that the response of the tissues is directly proportional to the doseof the tissues is directly proportional to the dose

The nonthreshold dose-response curve suggests The nonthreshold dose-response curve suggests that no matter how small the amount of radiation that no matter how small the amount of radiation received, some biologic damage occursreceived, some biologic damage occurs


Stochastic and Nonstochastic Stochastic and Nonstochastic Radiation EffectsRadiation Effects

Haring (p. 40)Haring (p. 40) Stochastic effectsStochastic effects

A direct function of the doseA direct function of the dose No dose threshold; effects do not depend on the No dose threshold; effects do not depend on the

magnitude of the absorbed dosemagnitude of the absorbed dose• Examples - cancer and genetic mutationsExamples - cancer and genetic mutations

Nonstochastic (deterministic) effectsNonstochastic (deterministic) effects Somatic effects that have a threshold; effects Somatic effects that have a threshold; effects

increase in severity with increasing absorbed doseincrease in severity with increasing absorbed dose• Examples: erythema, loss of hair, cataracts, and Examples: erythema, loss of hair, cataracts, and

decreased fertilitydecreased fertility


Sequence of Radiation InjurySequence of Radiation Injury

Haring (p. 41)Haring (p. 41) Latent periodLatent period

The time that elapses between exposure to The time that elapses between exposure to ionizing radiation and the appearance of ionizing radiation and the appearance of observable clinical signsobservable clinical signs

Depends on the total dose of radiation received Depends on the total dose of radiation received and the amount of time it took to receive the doseand the amount of time it took to receive the dose

Period of injuryPeriod of injury A variety of cellular injuries may resultA variety of cellular injuries may result


Radiation Injury Sequence, Radiation Injury Sequence, Repair, and AccumulationRepair, and Accumulation

Haring (pp. 41-42) (Table 4-1)Haring (pp. 41-42) (Table 4-1)

Recovery periodRecovery period Depending on a number of factors, cells can repair Depending on a number of factors, cells can repair

the damage caused by radiation the damage caused by radiation

Cumulative effectsCumulative effects Effects of radiation exposure are additiveEffects of radiation exposure are additive Unrepaired damage accumulates in tissuesUnrepaired damage accumulates in tissues


Determining Factors for Radiation InjuryDetermining Factors for Radiation Injury

Haring (pp. 41-42)Haring (pp. 41-42)

Total doseTotal dose Dose rateDose rate Amount of tissue irradiatedAmount of tissue irradiated Cell sensitivity Cell sensitivity AgeAge


Radiation EffectsRadiation Effects

Short- and long-term effectsShort- and long-term effects Somatic and genetic effectsSomatic and genetic effects Radiation effects on cellsRadiation effects on cells Radiation effects on tissues and organsRadiation effects on tissues and organs


Short- and Long-Term EffectsShort- and Long-Term Effects

Haring (p. 51)Haring (p. 51) Short-term effectsShort-term effects

Associated with large doses of radiation in a short Associated with large doses of radiation in a short amount of timeamount of time

Acute radiation syndrome (ARS)Acute radiation syndrome (ARS)• Includes nausea, vomiting, diarrhea, hair loss, Includes nausea, vomiting, diarrhea, hair loss,

hemorrhagehemorrhage Long-term effectsLong-term effects

Small doses absorbed repeatedly over a long Small doses absorbed repeatedly over a long period of timeperiod of time

Effects seen after years, decades, or generationsEffects seen after years, decades, or generations• Cancer, birth abnormalities, genetic defects Cancer, birth abnormalities, genetic defects


Somatic and Genetic EffectsSomatic and Genetic Effects

Haring (p. 42) (Fig. 4-5)Haring (p. 42) (Fig. 4-5)

Somatic cellsSomatic cells All cells in the body except the reproductive cellsAll cells in the body except the reproductive cells

Genetic cellsGenetic cells The reproductive cellsThe reproductive cells

Biologic effects of radiation can be classified Biologic effects of radiation can be classified as somatic or geneticas somatic or genetic


Somatic and Genetic EffectsSomatic and Genetic Effects

Somatic effectsSomatic effects Seen in the person irradiatedSeen in the person irradiated Not seen in future generationsNot seen in future generations

Genetic effectsGenetic effects Not seen in the person irradiatedNot seen in the person irradiated Passed on to future generationsPassed on to future generations


Radiation Effects on CellsRadiation Effects on Cells

Haring (p. 43) (Table 4-2)Haring (p. 43) (Table 4-2)

A cell that is sensitive to radiation is termed A cell that is sensitive to radiation is termed radiosensitive;radiosensitive; one that is resistant is termed one that is resistant is termed radioresistantradioresistant

The response is determined byThe response is determined by Mitotic activity Mitotic activity Cell differentiation Cell differentiation Cell metabolism Cell metabolism


Radiation Effects Radiation Effects on Tissues and Organson Tissues and Organs


Radiosensitive organsRadiosensitive organs Lymphoid tissueLymphoid tissue Bone marrowBone marrow TestesTestes IntestinesIntestines

Radioresistant tissuesRadioresistant tissues Salivary glandsSalivary glands KidneyKidney LiverLiver


Radiation Effects Radiation Effects on Tissues and Organson Tissues and Organs


Critical organCritical organ An organ that, if damaged, diminishes the quality An organ that, if damaged, diminishes the quality

of a person’s lifeof a person’s life

Critical organs exposed during dental Critical organs exposed during dental radiographic procedures includeradiographic procedures include SkinSkin Thyroid glandThyroid gland Lens of the eyeLens of the eye Bone marrowBone marrow


Radiation MeasurementsRadiation Measurements

Units of measurementUnits of measurement Exposure measurementExposure measurement Dose measurementDose measurement Dose equivalent measurementDose equivalent measurement


Units of MeasurementUnits of Measurement

Haring (pp. 43-44) (Tables 4-3, 4-4)Haring (pp. 43-44) (Tables 4-3, 4-4)

Traditional (older) units of radiation Traditional (older) units of radiation measurementmeasurement Roentgen (R)Roentgen (R) Radiation absorbed dose (rad)Radiation absorbed dose (rad) Roentgen equivalent (in) man (rem)Roentgen equivalent (in) man (rem)

SI (newer) units of radiation measurementSI (newer) units of radiation measurement Coulombs/kilogram (C/kg)Coulombs/kilogram (C/kg) Gray (Gy)Gray (Gy) Sievert (Sv)Sievert (Sv)


Exposure MeasurementExposure Measurement


RoentgenRoentgen Measures radiation by determining the amount of Measures radiation by determining the amount of

ionization that occurs in airionization that occurs in air Does not describe the amount of radiation Does not describe the amount of radiation

absorbedabsorbed

No SI equivalentNo SI equivalent Exposure is stated in coulombs per kilogramExposure is stated in coulombs per kilogram


Dose MeasurementDose Measurement


The amount of energy absorbed by tissueThe amount of energy absorbed by tissue Traditional unit is the rad (radiation absorbed dose)Traditional unit is the rad (radiation absorbed dose)

SI equivalent is the graySI equivalent is the gray 1 Gy = 100 rads1 Gy = 100 rads


Dose Equivalent MeasurementDose Equivalent Measurement


Used to compare biologic effects of different Used to compare biologic effects of different kinds of radiationkinds of radiation Traditional unit is the rem (roentgen equivalent man)Traditional unit is the rem (roentgen equivalent man)

SI equivalent is the sievert SI equivalent is the sievert 1 Sv = 100 rems1 Sv = 100 rems


Measurements Used Measurements Used in Dental Radiographyin Dental Radiography


Milli means 1/1000Milli means 1/1000 Used to express the small doses used in dental Used to express the small doses used in dental

radiographyradiography


Radiation RisksRadiation Risks

Sources of radiation exposureSources of radiation exposure Risk and risk estimatesRisk and risk estimates Dental radiation and exposure risksDental radiation and exposure risks Patient exposure and dosePatient exposure and dose Risk versus benefit of dental radiographsRisk versus benefit of dental radiographs


Sources of Radiation ExposureSources of Radiation Exposure

Haring (p. 45) (Table 4-5)Haring (p. 45) (Table 4-5)

Natural background radiationNatural background radiation A form of ionizing radiation that is ubiquitous in A form of ionizing radiation that is ubiquitous in

the environmentthe environment• Cosmic radiationCosmic radiation

Stars and sunStars and sun

• Terrestrial radiationTerrestrial radiation Radioactive materials in the earth and airRadioactive materials in the earth and air

In the U.S. the average dose of background In the U.S. the average dose of background radiation received by an individual ranges from radiation received by an individual ranges from 150 to 300 mrads per year150 to 300 mrads per year


Sources of Radiation ExposureSources of Radiation Exposure

Artificial or humanmade radiation Artificial or humanmade radiation Resulting from modern technologyResulting from modern technology

• Includes consumer products, fallout from atomic Includes consumer products, fallout from atomic weapons, weapons production, and the nuclear fuel cycleweapons, weapons production, and the nuclear fuel cycle

• Medical radiation including medical radiographic Medical radiation including medical radiographic procedures, dental radiography, fluoroscopy, nuclear procedures, dental radiography, fluoroscopy, nuclear medicine, and radiation therapymedicine, and radiation therapy


Risk and Risk EstimatesRisk and Risk Estimates


““The potential risk of dental radiography The potential risk of dental radiography inducing a fatal cancer in an individual has inducing a fatal cancer in an individual has been estimated to be 3 in 1 million”been estimated to be 3 in 1 million”

““The risk of a person developing a cancer The risk of a person developing a cancer spontaneously is much higher, or 3300 in 1 spontaneously is much higher, or 3300 in 1 million”million”


Risk and Risk EstimatesRisk and Risk Estimates


1 in a million risks of a fatal outcome1 in a million risks of a fatal outcome 10 miles on a bicycle10 miles on a bicycle 300 miles in an auto300 miles in an auto 1000 miles in an airplane1000 miles in an airplane Smoking 1.4 cigarettes a day Smoking 1.4 cigarettes a day


Dental Radiation Dental Radiation and Exposure Risksand Exposure Risks


Risk estimatesRisk estimates Thyroid glandThyroid gland Bone marrowBone marrow SkinSkin EyesEyes


Patient Exposure and DosePatient Exposure and Dose

Haring (pp. 46-47) (Table 4-6)Haring (pp. 46-47) (Table 4-6)

Film speedFilm speed CollimationCollimation TechniqueTechnique Exposure factorsExposure factors


Risk versus Benefit Risk versus Benefit of Dental Radiographsof Dental Radiographs


““Dental radiographs should be prescribed for Dental radiographs should be prescribed for a patient only when the benefit of disease a patient only when the benefit of disease detection outweighs the risk of biologic detection outweighs the risk of biologic damage”damage” When dental radiographs are properly prescribed When dental radiographs are properly prescribed

and exposed, the benefit of disease detection far and exposed, the benefit of disease detection far outweighs the risk of damageoutweighs the risk of damage



Chapter 5 reading:Chapter 5 reading: Haring (pp. 51-64)Haring (pp. 51-64)

Dh 111 radiation biology (ch.4) power point

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