Biological response and Biological response and radiation safety practicesradiation safety practices

BIOLOGICAL RESPONSE BIOLOGICAL RESPONSE AND RADIATION SAFETY AND RADIATION SAFETY PRACTICESPRACTICES

X-ray interactions in the patientRadiation exposuresRadiation measurement unitsMethods of detecting radiationBiological effects of radiation exposureAcute Radiation SyndromeSub-syndromes-hemopoietic, GI, CNSRadiation ProtectionALARA

TerminologyTerminology

NCRP R, roentgen,

coulombs/kg rad rem Gray Sievert Curie, Becquerel Effective does Quality factor Threshold ALARA

OSL Film badge TLD Pocket dosimeter Field survey instruments Geiger-Müller counter Cutie pie Somatic effect Genetic effect Acute Radiation

Syndrome(ARS)

Radiation ExposureRadiation Exposure

Exposure Measurements Methods of Measuring

Units of measure International unitsBritish UnitsUnit conversions

Film badgeOSLTLDPocket dosimeterField Survey

Instruments

What happens to our x-What happens to our x-ray?ray?

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PATIENT INTERACTIONSPATIENT INTERACTIONS

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Classical (Coherent) Scattering

Classical (Coherent) Scattering

Excitation of the total complement of atomic electrons occurs as a result of interaction with the incident photon

No ionization takes place

Electrons in shells “vibrate”

Small heat is released The photon is

scattered in different directions

Energies below 10kV

Patient Interactions

COMPTON SCATTERING

1. Outer shell electron in body

2. Interacts with x-ray photon from the tube

3. Moderate energy electron

Patient Interactions

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Patient Interactions

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photoelectron

Incoming photon interacts with inner shell electron. The “knocked-out” electron is called a photoelectron. The energy of the incoming photon is absorbed.

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Patient Interactions

Patient Interactions

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X-rays interact with Patient’s X-rays interact with Patient’s body to cause changes in cells. body to cause changes in cells.

Interaction in Interaction in the body beginthe body beginat the atomic at the atomic

levellevel

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Patient Interactions:Patient Interactions:Interactions of X-rays with matterInteractions of X-rays with matter

1. No interaction: X-ray passes completely and get to image receptor

2. Complete absorption: no x-rays get to image receptor

3. Partial absorption with scatter-some x-rays get to image receptor but some get scattered

X-ray photons can change X-ray photons can change cellscells

Patient InteractionsPatient Interactions

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RADIATION RADIATION EXPOSURESEXPOSURES

To Keep Ourselves Safe:◦Measure exposure◦Determine levels at which damage occurs

Measuring ExposureMeasuring ExposureUnits of Measure

◦ International Units C/kg3 Gray Sieverts Becquerel

◦ British Units Roentgen Rad Rem Curie

Exposure: Measured in airExposure: Measured in air

Absorbed DoseAbsorbed Dose

Radiation EquivalentRadiation Equivalent

RADS REMSRADS REMSrads

Grays

Patient absorbed dose

rems

Sieverts

Employee(technologists) =

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In diagnostic radiology:

1 roentgen = 1 rad = 1 rem

Comparison of UnitsComparison of UnitsExposure R C/kg 1R=2.58x

10-4 C/kgAbsorbed Dose

rad Gray 1rad=.01Gray1Gray=100rad

Dose Equivalent

rem Sievert 1rem=.01Sv1Sv=100rem

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In diagnostic radiology:

1 roentgen = 1 rad = 1 rem

Unit Conversions:Unit Conversions:A normal chest x-ray exposes the patient to approximately 15mR. How many roentgens is that?

A CT examination results in a patient dose of 4000 mrad. How many gray is that?

Annual exposure dose for a technologist is 5 rems. What is that in Sieverts? mSv?

You Receive ~620 millirem per year. According to stats from the US Nuclear Regulatory Commission average yearly exposure is roughly 620 millirem--half of which comes from natural sources (cosmic radiation, from the soil, radon, etc) and half comes from manmade sources. Note that geography can play a big part in that. In Colorado, for example, natural radiation exposure can be 1000 mrem per year due to higher altitude.What is your exposure in mSv?What is your exposure in mSv if you live in Colorado?

A patient left a head of lettuce in the x-ray exam room. The lettuce received a dose of 10mrad. How many Gr is that?

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Permissible Permissible Occupational DoseOccupational Dose

Annual dose : 5 Rem/year 50mSv/year 5000 mremCumulative Dose 1 rem x age or 10mSv x

age

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PUBLIC EXPOSUREPUBLIC EXPOSURE NON MEDICAL EXPOSURENON MEDICAL EXPOSURE

10 % of Occupational exposure0.5 rad or 500 mrad or 5mGray

Under age 18 and Students 0.1 rem

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Pregnancy & Embryo Pregnancy & Embryo

Mother occupational worker◦ 5 rem

Baby ◦ .5 rem/ year◦ .05 rem/month

Methods of MeasuringMethods of Measuring

Summary of Monitoring Summary of Monitoring DevicesDevices

monitoring device sensing material readability advantages disadvantages common usage

Film Badges filmchanged every month,

reading comes in a monthly report from company

least expensivenot instant reading, prone

to other factors such as heat, moisture, pressure

technologist, radiation personnel

Optically Stimulated Luminescence

Device

aluminum oxide crystals

changed 1-2 months, reading comes in a report from

company

more sensitve than film, not prone to damge from heat,

moisture, pressurenot reading immediately

technologist, radiation personnel

Thermolumuniescent Dosimeter

lithium floride crystals

can be worn up to 3 monthsonce crystals have been heated, can be re-used

no permanent recordtechnologist, radiation

personnel

Pocket Dosimeterionizes air in

chamberimmediate reading immediate reading

false readings common, no permanent record

technologist, radiation personnel

Field Survey Instruments

measures ionizations in air chamber

immediate readingnot used for personal

monitoringnot used for personal

monitoring

measures xray output of machines and areas known to

contain radioactivity

Exam 2 Next Week:

ALARA- As Low As Reasonably Achievable