Radiation Protection

Radiation ProtectionRadiation Protection

Robert L. Metzger, Ph.D.Robert L. Metzger, Ph.D.

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1. Sources of Exposure to Ionizing Radiation1. Sources of Exposure to Ionizing RadiationNaturally Occurring Radiation SourcesNaturally Occurring Radiation Sources

Annual average total effective Annual average total effective dose from exposure to ionizing dose from exposure to ionizing radiation in USA is approximately radiation in USA is approximately 3.6 mSv or 360 mrem3.6 mSv or 360 mrem [National [National Council on Radiation Protection Council on Radiation Protection and Measurement (NCRP)]and Measurement (NCRP)]

3 mSv or 300 mrem3 mSv or 300 mrem (80%) is from (80%) is from naturally occurring sourcesnaturally occurring sources RadonRadon Internal radiationInternal radiation Terrestrial radioactivityTerrestrial radioactivity Cosmic radiation Cosmic radiation

c.f. Bushberg, et al. The Essential Physics of Medical c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2Imaging, 2ndnd ed., p. 748. ed., p. 748.

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Radon Radon Biggest contributor to natural Biggest contributor to natural

background (background (2 mSv or 200 2 mSv or 200 mrem/yearmrem/year))

Radon (Rn-222) is a radioactive Radon (Rn-222) is a radioactive gas formed during the decay of gas formed during the decay of radiumradium

Radium is a decay product of Radium is a decay product of uranium found in the soil and has uranium found in the soil and has a half-life of 1620 yearsa half-life of 1620 years

Radon is an alpha emitter with a Radon is an alpha emitter with a half-life of approx. 4 dayshalf-life of approx. 4 days



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Radon Radon The progeny of radon are also The progeny of radon are also

radioactive, attach to aerosols and radioactive, attach to aerosols and are deposited in the lungsare deposited in the lungs

Bronchial mucosa is irradiated Bronchial mucosa is irradiated inducing bronchogenic cancer inducing bronchogenic cancer

Average concentration of radon Average concentration of radon outdoors is 4-8 Bq/moutdoors is 4-8 Bq/m33 (0.2-0.4 (0.2-0.4 pCi/L)pCi/L)

Indoors is 40 Bq/mIndoors is 40 Bq/m33 (1 pCi/L) (1 pCi/L) EPA Remedial action EPA Remedial action

recommended in excess of 160 recommended in excess of 160 Bq/mBq/m33 (4 pCi/L) (4 pCi/L)


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Internal Radiation Internal Radiation Second largest source of natural Second largest source of natural

background radiation (background radiation (0.4 mSv or 0.4 mSv or 4040 mrem/year) mrem/year)

Ingestion of food and water Ingestion of food and water containing primordial radionuclidescontaining primordial radionuclides

K-40 is most significantK-40 is most significant Skeletal muscle has the highest Skeletal muscle has the highest

concentration of potassium in the concentration of potassium in the bodybody



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Terrestrial or External Radiation Terrestrial or External Radiation Terrestrial radioactive materials that Terrestrial radioactive materials that

have been present on earth since have been present on earth since its formation are called primordial its formation are called primordial radionuclidesradionuclides

External radiation exposure, External radiation exposure, inhalation, ingestioninhalation, ingestion

0.28 mSv or 28 mrem/year0.28 mSv or 28 mrem/year ( ( 0.3 0.3 mSv or 30 mrem/year)mSv or 30 mrem/year)



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Cosmic Radiation Cosmic Radiation Cosmic rays are energetic protons Cosmic rays are energetic protons

and alpha particles which originate and alpha particles which originate in galaxiesin galaxies

Most cosmic rays interact with the Most cosmic rays interact with the atmosphere, with fewer than 0.05% atmosphere, with fewer than 0.05% reaching sea levelreaching sea level

0.27 mSv or 27 mrem/year0.27 mSv or 27 mrem/year ( ( 0.3 0.3 mSv or 30 mrem/year)mSv or 30 mrem/year)



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Cosmic Radiation Cosmic Radiation Exposures increase with altitude Exposures increase with altitude

approx. doubling every 1500 m as approx. doubling every 1500 m as there is less atmosphere to there is less atmosphere to attenuate the cosmic radiationattenuate the cosmic radiation

Leadville, Colorado at 3200 m, 1.25 Leadville, Colorado at 3200 m, 1.25 mSv/yearmSv/year

More at poles than equatorMore at poles than equator



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Cosmic Radiation Cosmic Radiation Air travel can add to individual’s Air travel can add to individual’s

cosmic exposurecosmic exposure Airline crews and frequent fliers Airline crews and frequent fliers

receive an additional receive an additional 1 mSv1 mSv 5 hour transcontinental flight will 5 hour transcontinental flight will

result in an equivalent dose of result in an equivalent dose of 25 25 Sv or 2.5 mremSv or 2.5 mrem

Apollo astronauts – 2.75 mSv or Apollo astronauts – 2.75 mSv or 275 mrem during a lunar mission275 mrem during a lunar mission



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Annual Dose EquivalentAnnual Dose Equivalent360 mrem360 mrem

11%

11%

8%

8%54%

1% 3% 4%

X-Rays Internal Terrestrial Cosmic

Radon Other Consumer Nuc Med

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Annual Dose - Other 1%Annual Dose - Other 1%

Occupational Dose – 0.3%Occupational Dose – 0.3% Fallout - <0.3%Fallout - <0.3% Nuclear Fuel Cycle – 0.1% Nuclear Fuel Cycle – 0.1% Miscellaneous – 0.1%Miscellaneous – 0.1% Natural Sources Account for 82% of total annual dose with only 18% Natural Sources Account for 82% of total annual dose with only 18%

coming from man made sources.coming from man made sources.

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Natural Sources of Radiation Natural Sources of Radiation

The variation of dose from the cosmic and terrestrial radiation is The variation of dose from the cosmic and terrestrial radiation is large depending on the area of the country (see handout).large depending on the area of the country (see handout).

High altitude areas have higher cosmic radiation levels (e.g. Denver, High altitude areas have higher cosmic radiation levels (e.g. Denver, Flagstaff)Flagstaff)

Areas that are heavily mineralized have higher terrestrial radiation Areas that are heavily mineralized have higher terrestrial radiation levels.levels.

Radon levels also vary significantly, but vary from home to home Radon levels also vary significantly, but vary from home to home rather than whole geographic areas (e.g. Watras house)rather than whole geographic areas (e.g. Watras house)

The overall variation in cosmic and terrestrial radiations exceed 100 The overall variation in cosmic and terrestrial radiations exceed 100 mrem per year and affect everyone in a city/area (e.g. Denver)mrem per year and affect everyone in a city/area (e.g. Denver)

Cancer incidence does not follow the background radiation levels at Cancer incidence does not follow the background radiation levels at all.all.

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Cancer Mortality in the USCancer Mortality in the US

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Legend for Mortality DataLegend for Mortality Data

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1.1. Sources of Exposure to Ionizing RadiationSources of Exposure to Ionizing RadiationTechnology Based Radiation SourcesTechnology Based Radiation Sources

60 mrem or 60 mrem or 0.6 mSv0.6 mSv

CT and CT and fluoroscopyfluoroscopyare highest are highest contributorscontributorsto medical to medical x-raysx-rays

c.f. Bushberg, et al. c.f. Bushberg, et al. The Essential The Essential Physics of Medical Physics of Medical Imaging, 2Imaging, 2ndnd ed., p. ed., p. 744.744.

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1 mSv for diagnostic radiology is lower than expected because it includes personnel who receive very small occupational exposures 15 mSv or more are typical of special procedures utilizing fluoroscopy and cine

1. Occupational Exposures1. Occupational Exposures


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1. Collective Effective Dose Equivalent1. Collective Effective Dose Equivalent

The product of the average effective dose equivalent and the size of the The product of the average effective dose equivalent and the size of the exposed population is the exposed population is the collective effective dose equivalentcollective effective dose equivalent

Expressed in person-sieverts (person-Sv or person-rem) [not used much Expressed in person-sieverts (person-Sv or person-rem) [not used much anymore]anymore]


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1. Genetically Significant Dose (GSD)1. Genetically Significant Dose (GSD)

The The genetically significant equivalent dose (GSD)genetically significant equivalent dose (GSD) is a dose parameter that is a dose parameter that is an index of potential genetic damageis an index of potential genetic damage

The GSD is defined as that equivalent dose that, if received by every The GSD is defined as that equivalent dose that, if received by every member of the population, would be expected to produce the same genetic member of the population, would be expected to produce the same genetic injury to the population as do the actual doses received by the irradiated injury to the population as do the actual doses received by the irradiated individualsindividuals

GSD is determined by taking the equivalent dose to the gonads of each GSD is determined by taking the equivalent dose to the gonads of each exposed individual and estimating the number of children expected for a exposed individual and estimating the number of children expected for a person of that age and sexperson of that age and sex

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1. Genetically Significant Dose (GSD)1. Genetically Significant Dose (GSD)


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1. Summary 1. Summary

The average annual effective dose equivalent to the US population The average annual effective dose equivalent to the US population from all radiation sources is 3.6 mSv/year or 360 mrem/yearfrom all radiation sources is 3.6 mSv/year or 360 mrem/year 3 mSv/year – naturally occurring sources3 mSv/year – naturally occurring sources

Radon – 2 mSvRadon – 2 mSv

0.6 mSv/year – technologically enhanced sources0.6 mSv/year – technologically enhanced sources Medical x-rays – 0.39 mSv or 39 mrem, Medical x-rays – 0.39 mSv or 39 mrem, Nuclear Medicine – 0.14 mSv or 14 mremNuclear Medicine – 0.14 mSv or 14 mrem Data is from mid – 80s. Current estimates are higher due to Data is from mid – 80s. Current estimates are higher due to

the increased use of CT. Recent estimates are 385 mrem the increased use of CT. Recent estimates are 385 mrem with 85 mrem due to medical.with 85 mrem due to medical.

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1. Summary 1. Summary

Collective effective dose equivalent (person-Sv or person-rem)Collective effective dose equivalent (person-Sv or person-rem) Product of the average effective dose equivalent and the size Product of the average effective dose equivalent and the size

of the exposed population (No longer used commonly)of the exposed population (No longer used commonly)

GSD (mSv or mrem)GSD (mSv or mrem) Used to express genetic risk to the whole population from a Used to express genetic risk to the whole population from a

source of radiation exposuresource of radiation exposure GSD from diagnostic x-rays is 0.2 mSv or 20 mrem GSD from diagnostic x-rays is 0.2 mSv or 20 mrem GSD from nuclear medicine is 0.02 mSv or 2 mremGSD from nuclear medicine is 0.02 mSv or 2 mrem

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Raphex 2002 General QuestionRaphex 2002 General Question

G87.G87. The annual average The annual average natural natural background radiation dose to background radiation dose to members of the public in the United States, members of the public in the United States, excluding excluding radon, is radon, is approximately ________ mrem.approximately ________ mrem.

A. 10A. 10 B. 50B. 50 C. 100C. 100 D. 200D. 200 E. 400E. 400

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QuestionQuestion

1. The Genetically significant dose (GSD) for diagnostic x-rays and 1. The Genetically significant dose (GSD) for diagnostic x-rays and nuclear medicine in the US is:nuclear medicine in the US is:

A. 2 mSv and 0.20 mSvA. 2 mSv and 0.20 mSv B. 0.20 mSv and 2 mSvB. 0.20 mSv and 2 mSv C. 0.02 mSv and 0.20 mSvC. 0.02 mSv and 0.20 mSv D. 0.20 mSv and 0.02 mSvD. 0.20 mSv and 0.02 mSv

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2. Personnel Dosimetry2. Personnel DosimetryFilm BadgesFilm Badges

A film pack (A) consists of a black envelope (B) containing film (C) placed inside a A film pack (A) consists of a black envelope (B) containing film (C) placed inside a special plastic film holder (D)special plastic film holder (D)

Using metal filters typically lead (G), copper (H) and aluminum (I), the relative optical Using metal filters typically lead (G), copper (H) and aluminum (I), the relative optical densities of the film underneath the filters can be used to identify the general energy densities of the film underneath the filters can be used to identify the general energy range of the radiation and allow for the conversion of the film dose to tissue doserange of the radiation and allow for the conversion of the film dose to tissue dose

Open window (J) where film is not covered by a filter or plastic and is used to detect Open window (J) where film is not covered by a filter or plastic and is used to detect medium and high-energy beta radiationmedium and high-energy beta radiation

c.f. Bushberg, et al. The c.f. Bushberg, et al. The Essential Physics of Essential Physics of Medical Imaging, 2Medical Imaging, 2ndnd ed., p. 749.ed., p. 749.

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2. Personnel Dosimetry2. Personnel DosimetryFilm BadgesFilm Badges

Most film badges can record doses from about 100 Most film badges can record doses from about 100 Gy to 15 Gy (10 mrad to Gy to 15 Gy (10 mrad to 1500 rad) for photons and from 500 1500 rad) for photons and from 500 Gy to 10 Gy (50 mrad to 1,000 rad) for Gy to 10 Gy (50 mrad to 1,000 rad) for beta radiationbeta radiation

The dosimetry report lists the “shallow” equivalent dose, corresponding to the The dosimetry report lists the “shallow” equivalent dose, corresponding to the skin dose, and the “deep” equivalent dose, corresponding to penetrating skin dose, and the “deep” equivalent dose, corresponding to penetrating radiationradiation

Generally placed at waist level or shirt-pocket levelGenerally placed at waist level or shirt-pocket level For fluoroscopy, placed at collar level outside the lead apron to measure For fluoroscopy, placed at collar level outside the lead apron to measure

radiation dose to thyroid and lens of eyeradiation dose to thyroid and lens of eye

Pregnant radiation workers typically wear a second badge at waist level Pregnant radiation workers typically wear a second badge at waist level (behind the lead apron, if used) to assess the fetal dose(behind the lead apron, if used) to assess the fetal dose

Excessive moisture or heat will damage film inside badgeExcessive moisture or heat will damage film inside badge

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TLD is a dosimeter in which consists of a scintillator in which electrons TLD is a dosimeter in which consists of a scintillator in which electrons become trapped in excited states after interactions with ionizing radiationbecome trapped in excited states after interactions with ionizing radiation

If the scintillator is later heated, the electrons can then fall to their ground If the scintillator is later heated, the electrons can then fall to their ground state with the emission of lightstate with the emission of light

Thermoluminescent (TL) means emitting light when heated Thermoluminescent (TL) means emitting light when heated

The amount of light emitted by the TLD is proportional to the amount of The amount of light emitted by the TLD is proportional to the amount of energy absorbed by the TLDenergy absorbed by the TLD

After TLD has been read, it may be baked in an oven and reusedAfter TLD has been read, it may be baked in an oven and reused

2. Personnel Dosimetry2. Personnel DosimetryThermoluminescent (TLD) Dosimeters Thermoluminescent (TLD) Dosimeters

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2. Personnel Dosimetry2. Personnel DosimetryThermoluminescent (TLD) DosimetersThermoluminescent (TLD) Dosimeters

Lithium Fluoride (LiF) is one of the most useful TLD materialsLithium Fluoride (LiF) is one of the most useful TLD materials LiF TLDs have a wide dose response range of 10 LiF TLDs have a wide dose response range of 10 Sv to 10Sv to 1033 mSv (1 mrem mSv (1 mrem

to 10to 1055 rem) rem) Used in nuclear medicine to record extremity exposuresUsed in nuclear medicine to record extremity exposures

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2. Personnel Dosimetry2. Personnel DosimetryOptically Stimulated Luminescent (OSL) Dosimeters Optically Stimulated Luminescent (OSL) Dosimeters

The principle of OSL is similar to TLDs except that the light emission is The principle of OSL is similar to TLDs except that the light emission is stimulated by a laser light instead of heatstimulated by a laser light instead of heat

Crystalline aluminum oxide activated with carbon (Al2O3:C) is commonly Crystalline aluminum oxide activated with carbon (Al2O3:C) is commonly usedused

Broad dose response range like TLDsBroad dose response range like TLDs They can be reread several timesThey can be reread several times

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2. Personnel Dosimetry2. Personnel DosimetryPocket Dosimeters Pocket Dosimeters

Major disadvantage to film and Major disadvantage to film and TLD dosimeters is that the TLD dosimeters is that the accumulated exposure is not accumulated exposure is not immediately indicatedimmediately indicated

Pocket dosimeters measure Pocket dosimeters measure radiation exposure, which can be radiation exposure, which can be read instantaneouslyread instantaneously

Can measure exposures from 0 to Can measure exposures from 0 to 200 mR or 0 to 5 R200 mR or 0 to 5 R

Analog or digitalAnalog or digital


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2. Summary2. Summary


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Raphex 2002 General QuestionsRaphex 2002 General Questions

G95.G95. Film badges: Film badges:

A. Can measure only the total dose of radiation, but cannot A. Can measure only the total dose of radiation, but cannot distinguish between low and high energy x-rays.distinguish between low and high energy x-rays.

B. Can measure exposures of 1 mR.B. Can measure exposures of 1 mR. C. Are insensitive to heat.C. Are insensitive to heat. D. Use the optical density of the film to measure dose.D. Use the optical density of the film to measure dose.

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3. Radiation Detection Equipment In Radiation 3. Radiation Detection Equipment In Radiation SafetySafety

Geiger-Mueller Survey InstrumentsGeiger-Mueller Survey Instruments Measurements are in counts per minute (cpm)Measurements are in counts per minute (cpm) Surveys radioactive contamination in nuclear medicineSurveys radioactive contamination in nuclear medicine Are extremely sensitive to charged particulate radiations with sufficient Are extremely sensitive to charged particulate radiations with sufficient

energy to penetrate the survey meter windowenergy to penetrate the survey meter window Are relatively insensitive to x- and gamma radiationsAre relatively insensitive to x- and gamma radiations

Portable Ionization ChambersPortable Ionization Chambers Used when accurate measurements of radiation exposure are required, Used when accurate measurements of radiation exposure are required,

measurement of x-ray machine outputsmeasurement of x-ray machine outputs Measure 1 mR/hr to 500 R/hrMeasure 1 mR/hr to 500 R/hr

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4. Radiation Protection and Exposure Control4. Radiation Protection and Exposure Control

There are four principal methods by which radiation exposures to persons There are four principal methods by which radiation exposures to persons can be minimized: time, distance, shielding and contamination controlcan be minimized: time, distance, shielding and contamination control TimeTime

reducing time spend near a radiation sourcereducing time spend near a radiation source DistanceDistance

inverse square lawinverse square law For diagnostic x-rays, a good rule of thumb is that at 1 m from a For diagnostic x-rays, a good rule of thumb is that at 1 m from a

patient at 90 degrees to the incident beam, patient at 90 degrees to the incident beam, the radiation intensity is the radiation intensity is 0.1% to 0.15% (0.001 to 0.0015) of the intensity of the beam 0.1% to 0.15% (0.001 to 0.0015) of the intensity of the beam incident upon the patientincident upon the patient for a 400 cm for a 400 cm22 area field area area field area

The NCRP recommends that personnel should stand The NCRP recommends that personnel should stand at least 2 m at least 2 m from the x-ray tubefrom the x-ray tube and the patient and behind a shielded barrier or and the patient and behind a shielded barrier or out of the room, whenever possibleout of the room, whenever possible

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Shielding is used to reduce exposure to patients, staff and the publicShielding is used to reduce exposure to patients, staff and the public Shielding against primary (focal spot), scattered (patient) and leakage (Shielding against primary (focal spot), scattered (patient) and leakage (x-ray x-ray

tube housing, limited to 100 mR/hr at 1 m from housingtube housing, limited to 100 mR/hr at 1 m from housing) radiation) radiation

4. Radiation Protection and Exposure Control4. Radiation Protection and Exposure ControlShieldingShielding

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Shielding – NCRP 49 vs. 147Shielding – NCRP 49 vs. 147

The Bushberg X-Ray shielding section is based on NCRP 49 which The Bushberg X-Ray shielding section is based on NCRP 49 which is obsolete and out of print. Bushberg notes that it is badly out of is obsolete and out of print. Bushberg notes that it is badly out of date.date.

NCRP 147 replaced NCRP 49 in 2005. It should be used for all NCRP 147 replaced NCRP 49 in 2005. It should be used for all shielding calculations.shielding calculations.

NCRP 147 uses a different methodology to calculate the shielding NCRP 147 uses a different methodology to calculate the shielding values and uses much more realistic values for occupancy, tube values and uses much more realistic values for occupancy, tube kVps, weekly mAs, and film/screen speeds.kVps, weekly mAs, and film/screen speeds.

It eliminates the gross overshielding resulting from the use of NCRP It eliminates the gross overshielding resulting from the use of NCRP 49 with the lowered non-occupational dose limits.49 with the lowered non-occupational dose limits.

NCRP 147 also provides shielding methodologies for CT and othr NCRP 147 also provides shielding methodologies for CT and othr modalities.modalities.

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Shielding calculations depend on:Shielding calculations depend on: radiation exposure levelradiation exposure level (mR/week) (mR/week) depends on techniques and patient depends on techniques and patient

loadload workload workload (amount of x-rays produced per week), (amount of x-rays produced per week), W (mA.min/week)W (mA.min/week)

use factor, Uuse factor, U,, indicates the fraction of time during which the radiation indicates the fraction of time during which the radiation under consideration is directed at a particular barrierunder consideration is directed at a particular barrier

a wall that intercepts the primary beam is called a primary barrier a wall that intercepts the primary beam is called a primary barrier and is assigned a use factor according to typical room useand is assigned a use factor according to typical room use

U ranges between 0 and 1, secondary barriers have a use factor of U ranges between 0 and 1, secondary barriers have a use factor of 11


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Shielding calculations depend on:Shielding calculations depend on: occupancy factor, T,occupancy factor, T, indicates the fraction of time during a week that a indicates the fraction of time during a week that a

single individual might spend in an adjacent areasingle individual might spend in an adjacent area T = 1 for full occupancy (work areas, offices etc.)T = 1 for full occupancy (work areas, offices etc.) T = 1/5 for partial occupancy (corridors, rest rooms etc.)T = 1/5 for partial occupancy (corridors, rest rooms etc.) T = 1/16 for occasional occupancy (waiting rooms, toilets, etc.)T = 1/16 for occasional occupancy (waiting rooms, toilets, etc.) T = 1/40T = 1/40thth for landscaping, etc. for landscaping, etc.

Distance, dDistance, d,, measured from source of radiation to the area to be measured from source of radiation to the area to be protectedprotected


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Shielding calculations determine the thickness of an attenuating material Shielding calculations determine the thickness of an attenuating material required to reduce radiation exposure to acceptable levelsrequired to reduce radiation exposure to acceptable levels

1 mSv/year or 100 mrem/year (2 mR/week) for non-occupational personnel 1 mSv/year or 100 mrem/year (2 mR/week) for non-occupational personnel (members of public and non-radiation workers)(members of public and non-radiation workers)

0.1 or 10 mR/week for controlled areas (pregnant worker limit)0.1 or 10 mR/week for controlled areas (pregnant worker limit)


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Lead usually used for shielding and specified as weight per square foot Lead usually used for shielding and specified as weight per square foot (lb/ft(lb/ft22). ). Typically 2 lb/ftTypically 2 lb/ft22 (0.8 mm or 1/32 (0.8 mm or 1/32thth inch) or 4 lb/ft inch) or 4 lb/ft22 (1.6 mm or 1/16 (1.6 mm or 1/16thth inch) is sufficient for diagnostic radiologyinch) is sufficient for diagnostic radiology

Calculated using HVL and TVL of the materialCalculated using HVL and TVL of the material [(1/2) [(1/2)n n – reduction in beam – reduction in beam intensity, n is HVL]intensity, n is HVL]

Shielding material used from base of floor to a height of 7 feetShielding material used from base of floor to a height of 7 feet Acrylic, leaded glass, gypsum drywall, steel are other materials used Acrylic, leaded glass, gypsum drywall, steel are other materials used

besides lead for shieldingbesides lead for shielding


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CT scanner shielding (Use NCRP 147 with web based scatter CT scanner shielding (Use NCRP 147 with web based scatter values)values)

Personnel protection in Dx Radiology (lead aprons, thyroid shields Personnel protection in Dx Radiology (lead aprons, thyroid shields etc., pg. 771 of Bushberg)etc., pg. 771 of Bushberg)

Shielding in nuclear medicineShielding in nuclear medicine Shielding in PET (Beware!) Undershielding in some clinics have led Shielding in PET (Beware!) Undershielding in some clinics have led

to high technologist and non-occupational doses. PET shielding to high technologist and non-occupational doses. PET shielding guide from AAPM is not published as yet. guide from AAPM is not published as yet.

4. Radiation Protection and Exposure Control4. Radiation Protection and Exposure Control

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Tube Voltage and Beam FiltrationTube Voltage and Beam Filtration Achieve an optimal balance between image quality and dose to the Achieve an optimal balance between image quality and dose to the

patientpatient Patient exposure can be reduced by using a higher kVp ad lower mAsPatient exposure can be reduced by using a higher kVp ad lower mAs

Increasing kVp increases transmission (less absorption) of x-rays Increasing kVp increases transmission (less absorption) of x-rays through the patientthrough the patient

Even though mR/mAs increases as kVp increases, an Even though mR/mAs increases as kVp increases, an accompanying reduction in mAs will decrease the incident exposure accompanying reduction in mAs will decrease the incident exposure to the patientto the patient

Contrast will decrease due to higher effective energy of the x-ray Contrast will decrease due to higher effective energy of the x-ray beambeam

4. Radiation Protection and Exposure Control4. Radiation Protection and Exposure ControlProtection of the Patient in Medical X-ray ImagingProtection of the Patient in Medical X-ray Imaging

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Tube Voltage and Beam FiltrationTube Voltage and Beam Filtration Filtration of the polychromatic x-ray energy spectrum can significantly Filtration of the polychromatic x-ray energy spectrum can significantly

reduce exposure by selectively attenuating the low-energy x-rays in the reduce exposure by selectively attenuating the low-energy x-rays in the beambeam

As the tube filtration increases, the beam becomes hardened (effective As the tube filtration increases, the beam becomes hardened (effective energy increases) and dose to patient decreases because fewer low-energy increases) and dose to patient decreases because fewer low-energy photons are in the incident beamenergy photons are in the incident beam

The amount of filtration that can be added is limited by the increased The amount of filtration that can be added is limited by the increased demands on tube loading to offset reduction in tube output, and the demands on tube loading to offset reduction in tube output, and the decreased contrast due to excessive beam hardeningdecreased contrast due to excessive beam hardening

Quality of x-ray beam is assessed by measuring the HVLQuality of x-ray beam is assessed by measuring the HVL


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Depth DoseDepth Dose

Recall Dose = Energy absorbed per gram.Recall Dose = Energy absorbed per gram. For soft radiations, the dose decreases dramatically with depth as the For soft radiations, the dose decreases dramatically with depth as the

patient’s body attenuates the beam.patient’s body attenuates the beam. The radiation dose at a given depth is the depth dose (rad).The radiation dose at a given depth is the depth dose (rad). The exposure at skin entrance (ESE) is the Roentgen exposure at the The exposure at skin entrance (ESE) is the Roentgen exposure at the

point where the radiation enters the body.point where the radiation enters the body.

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Depth DoseDepth Dose

Depth Dose for Medium Energy X-Ray

0102030405060708090100

0 5 10 15 20

Depth (cm)

Per

cent

Dep

th D

ose

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Field Area, Organ Shielding and GeometryField Area, Organ Shielding and Geometry Reducing field size limits the patient volume exposed to primary beam, Reducing field size limits the patient volume exposed to primary beam,

reduces the amount of scatter and thus radiation dose to adjacent reduces the amount of scatter and thus radiation dose to adjacent organs (scatter being reduced improves image contrast)organs (scatter being reduced improves image contrast)

Gonadal shielding can be used to protect the gonads from primary Gonadal shielding can be used to protect the gonads from primary radiation when the shadow of the shield does not interfere with the radiation when the shadow of the shield does not interfere with the anatomy under investigationanatomy under investigation

Increasing source-to-object distance (SOD) and source-to-image Increasing source-to-object distance (SOD) and source-to-image distance (SID) helps reduce dose (patient volume exposed decreased distance (SID) helps reduce dose (patient volume exposed decreased due to reduced beam divergence)due to reduced beam divergence)

For fixed SID (C-arm fluoro system), patient dose is reduced by For fixed SID (C-arm fluoro system), patient dose is reduced by increasing the SOD as much as possibleincreasing the SOD as much as possible

A minimum patient to focal spot distance of 20 cm is requiredA minimum patient to focal spot distance of 20 cm is required


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X-Ray Image ReceptorsX-Ray Image Receptors The speed of the image receptor determines the number of x-ray The speed of the image receptor determines the number of x-ray

photons and thus the patient dose necessary to achieve an appropriate photons and thus the patient dose necessary to achieve an appropriate signal levelsignal level

Higher speed system requires less exposure to produce the same Higher speed system requires less exposure to produce the same optical density and thus reduces dose to patientoptical density and thus reduces dose to patient

Either a faster screen (reduced spatial resolution) or faster film Either a faster screen (reduced spatial resolution) or faster film (increased quantum mottle) will reduce the incident exposure to the (increased quantum mottle) will reduce the incident exposure to the patientpatient


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X-Ray Image ReceptorsX-Ray Image Receptors Computed Radiography (CR) devices have a wide dynamic range so Computed Radiography (CR) devices have a wide dynamic range so

they compensate to some degree for under- and overexposure and can they compensate to some degree for under- and overexposure and can reduce retakesreduce retakes

CR roughly equivalent to 200 speed screen-film systemsCR roughly equivalent to 200 speed screen-film systems Techniques for extremities with CR devices should be used at higher Techniques for extremities with CR devices should be used at higher

exposure levels while exposures for pediatric patients should be used at exposure levels while exposures for pediatric patients should be used at increased speed (e.g. 400 speed) to reduce doseincreased speed (e.g. 400 speed) to reduce dose


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Computed Tomography Computed Tomography (CT)(CT)

Reduce mAs and Reduce mAs and perhaps kVp for perhaps kVp for thinner and pediatric thinner and pediatric patientspatients

Pediatric protocols Pediatric protocols required in AZ.required in AZ.

Modern MSCT Modern MSCT scanners – dose scanners – dose modulation, mA modulation, mA changes with patient changes with patient sizesize

c.f. Bushberg, et al. The Essential Physics of c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2Medical Imaging, 2ndnd ed., p. 779. ed., p. 779.

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Miscellaneous ConsiderationsMiscellaneous Considerations Careful identification of patientsCareful identification of patients Determination of pregnancy statusDetermination of pregnancy status Eliminate screening exams that only rarely detect pathologyEliminate screening exams that only rarely detect pathology ““yearly” dental exams may not be appropriate for all patientsyearly” dental exams may not be appropriate for all patients Use of high speed dental film reduces doseUse of high speed dental film reduces dose ““yearly” screening mammography exams not appropriate for women yearly” screening mammography exams not appropriate for women

younger than 35 to 40 years oldyounger than 35 to 40 years old Technique errors and high repeat rates can be avoided by posting Technique errors and high repeat rates can be avoided by posting

technique charts and using phototimingtechnique charts and using phototiming Good quality control program to eliminate equipment and processor Good quality control program to eliminate equipment and processor

problemsproblems


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Time, distance and shielding used to protect persons from radiation Time, distance and shielding used to protect persons from radiation exposureexposure

Shielding calculations depend on mR/week, workload, use factor, Shielding calculations depend on mR/week, workload, use factor, occupancy factor and distance from x-ray sourceoccupancy factor and distance from x-ray source

Typically 2 or 4 lb/ftTypically 2 or 4 lb/ft22 lead is sufficient for shielding in diagnostic lead is sufficient for shielding in diagnostic radiologyradiology

Calculated using HVL and TVL of the material [(1/2)Calculated using HVL and TVL of the material [(1/2)n n – reduction in – reduction in beam intensity, n is HVL]beam intensity, n is HVL]

Protect patient by adjusting kVp, mAs, filtration, field size, geometry Protect patient by adjusting kVp, mAs, filtration, field size, geometry and using organ shielding, using faster film-screen systems, and using organ shielding, using faster film-screen systems, eliminate screening chest and yearly dental examseliminate screening chest and yearly dental exams

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G92.G92. A shielding design for a diagnostic or therapy installation, A shielding design for a diagnostic or therapy installation, when there is no restriction on the beam direction, must:when there is no restriction on the beam direction, must:

A. Consider all walls as primary barriers.A. Consider all walls as primary barriers. B. Assign all walls a use factor (U) of 1.B. Assign all walls a use factor (U) of 1. C. Assign all areas adjacent to the installation an occupancy factor C. Assign all areas adjacent to the installation an occupancy factor

(T) of 1.(T) of 1. D. Shield all areas to a radiation level of 0.1 rem per week.D. Shield all areas to a radiation level of 0.1 rem per week. E. Shield such that adjacent areas will E. Shield such that adjacent areas will not not receive instantaneous receive instantaneous

dose rates greater than 2 mR/hr.dose rates greater than 2 mR/hr.

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G93.G93. The occupancy factor (T) is changed from 1/16 to 1/2 and the activity The occupancy factor (T) is changed from 1/16 to 1/2 and the activity factor (A) is doubled for a radiation source whose HVL is 0.3 mm Pb. In factor (A) is doubled for a radiation source whose HVL is 0.3 mm Pb. In order to maintain the same level of protection, _____ mm Pb must be order to maintain the same level of protection, _____ mm Pb must be added to the shielding.added to the shielding.

A. 0.3A. 0.3 B. 0.6B. 0.6 C. 0.9C. 0.9 D. 1.2D. 1.2 E. 1.5E. 1.5

The occupancy factor (T) is the fraction of time that the area is occupied. The occupancy factor (T) is the fraction of time that the area is occupied. Since T is increased by a factor of 8 and the activity (A) is doubled, the Since T is increased by a factor of 8 and the activity (A) is doubled, the exposure is increased by a factor of 16. Thus, 4 HVLs (2exposure is increased by a factor of 16. Thus, 4 HVLs (244 = 16) of lead are = 16) of lead are required to maintain the same radiation level. 0.3 mm xrequired to maintain the same radiation level. 0.3 mm x 4 = 1.2 mm4 = 1.2 mm Pb.Pb.


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5. Regulatory Agencies and Radiation Exposure 5. Regulatory Agencies and Radiation Exposure LimitsLimits

U.S. Nuclear Regulatory Commission (U.S. Nuclear Regulatory Commission (NRCNRC) regulates special nuclear ) regulates special nuclear material, source material, by-product material of nuclear fission, regulates material, source material, by-product material of nuclear fission, regulates the maximum permissible dose equivalent limitsthe maximum permissible dose equivalent limits Some states known as agreement states arrange with the NRC to self-Some states known as agreement states arrange with the NRC to self-

regulate medically related licensing and inspection requirements of regulate medically related licensing and inspection requirements of radioactive materialsradioactive materials

Food and Drug Administration (Food and Drug Administration (FDAFDA) regulates radiopharmaceutical ) regulates radiopharmaceutical development, manufacturing, performance and radiation safety development, manufacturing, performance and radiation safety requirements associated with the production of commercial x-ray equipmentrequirements associated with the production of commercial x-ray equipment

U.S. Department of Transportation (U.S. Department of Transportation (DOTDOT) regulates the transportation of ) regulates the transportation of radioactive materialsradioactive materials

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5. Advisory Bodies5. Advisory Bodies

National Council on Radiation Protection and Measurements (National Council on Radiation Protection and Measurements (NCRPNCRP)) Collect, analyze, develop and disseminate, in the public interest, Collect, analyze, develop and disseminate, in the public interest,

information and recommendations about radiation protection, radiation information and recommendations about radiation protection, radiation measurements, quantities and unitsmeasurements, quantities and units

International Commission on Radiological Protection (International Commission on Radiological Protection (ICRPICRP)) Similar to NCRP, however its international membership brings to bear a Similar to NCRP, however its international membership brings to bear a

variety of perspectives on radiation health issuesvariety of perspectives on radiation health issues

The NCRP and ICRP have published over 200 monographs containing The NCRP and ICRP have published over 200 monographs containing recommendations on a wide variety of radiation health issues that serve as recommendations on a wide variety of radiation health issues that serve as the reference documents from which many regulations are craftedthe reference documents from which many regulations are crafted

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5. Summing internal and external doses5. Summing internal and external doses

Dose from an internal exposure continues after the period of ingestion or Dose from an internal exposure continues after the period of ingestion or inhalation, until the radioactivity is eliminated by radioactive decay or inhalation, until the radioactivity is eliminated by radioactive decay or biologic removalbiologic removal

The committed dose equivalent (HThe committed dose equivalent (H50,T50,T) is the dose equivalent to a tissue or ) is the dose equivalent to a tissue or organ over the 50 years following the ingestion or inhalation of organ over the 50 years following the ingestion or inhalation of radioactivityradioactivity

The committed effective dose equivalent (The committed effective dose equivalent (CEDECEDE) is a weighted average of ) is a weighted average of the committed dose equivalents to the various tissues and organs of the the committed dose equivalents to the various tissues and organs of the bodybody

CEDE = CEDE = wwTT H H50,T50,T

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5. Summing internal and external doses5. Summing internal and external doses

To sum the internal and external doses to any individual tissue or organ, To sum the internal and external doses to any individual tissue or organ, the deep dose equivalent (indicated by the dosimeter) and the the deep dose equivalent (indicated by the dosimeter) and the committed dose equivalent to the organ are addedcommitted dose equivalent to the organ are added

The sum of the deep dose equivalent and the committed dose The sum of the deep dose equivalent and the committed dose equivalent is called the total effective dose equivalent (equivalent is called the total effective dose equivalent (TEDETEDE) )

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5. Dose Limits5. Dose Limits


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5. As Low As Reasonably Achievable (ALARA) 5. As Low As Reasonably Achievable (ALARA) PrinciplePrinciple

Dose limits to workers and the public are regarded as upper limits rather Dose limits to workers and the public are regarded as upper limits rather than as acceptable doses or thresholds of safetythan as acceptable doses or thresholds of safety

In addition to the dose limits, all licenses are required to employ good health In addition to the dose limits, all licenses are required to employ good health physics practices and implement radiation safety programs to ensure that physics practices and implement radiation safety programs to ensure that radiation exposures are kept radiation exposures are kept as low as reasonably achievable (ALARA)as low as reasonably achievable (ALARA), , taking societal and economic factors into considerationtaking societal and economic factors into consideration

The ALARA doctrine is the driving force for many of the policies, The ALARA doctrine is the driving force for many of the policies, procedures, and practices in radiation laboratories, and represents a procedures, and practices in radiation laboratories, and represents a commitment by both employee and employer to minimize radiation commitment by both employee and employer to minimize radiation exposure to staff, the public, and the environment to the greatest extent exposure to staff, the public, and the environment to the greatest extent possiblepossible

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Regulatory agencies, advisory bodies and their functionsRegulatory agencies, advisory bodies and their functions Dose limitsDose limits

Occupational and public dose limitsOccupational and public dose limits Organ limitsOrgan limits

ALARA principleALARA principle

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G82. G82. The annual recommended dose to the lens of the eye of a The annual recommended dose to the lens of the eye of a radiation worker is:radiation worker is:

A. 500 mSv (50 rem)A. 500 mSv (50 rem) B. 150 mSv (15 rem)B. 150 mSv (15 rem) C. 50 mSv (5 rem)C. 50 mSv (5 rem) D. 5 mSv (500 mrem)D. 5 mSv (500 mrem) E. 1 mSv (100 mrem)E. 1 mSv (100 mrem)

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G91. G91. The NRC and state regulatorsThe NRC and state regulators require require radiation monitoring of hospital radiation monitoring of hospital staff in which categories?staff in which categories?

1. Anyone who regularly comes into the radiology department (e.g., cleaning 1. Anyone who regularly comes into the radiology department (e.g., cleaning staff).staff).

2. Anyone who could receive a 2. Anyone who could receive a measurablemeasurable exposure, but on an irregular exposure, but on an irregular basis (e.g., nurses who work in areas where "portable" films are taken).basis (e.g., nurses who work in areas where "portable" films are taken).

3.3. Workers who are likely to receive an occupational dose of between 10 Workers who are likely to receive an occupational dose of between 10 and 100 mrem per year.and 100 mrem per year.

4. Workers who are likely to receive an occupational dose of greater than 4. Workers who are likely to receive an occupational dose of greater than 1,250 mrem per year.1,250 mrem per year.

5. Workers who have regular access to "high radiation areas.”5. Workers who have regular access to "high radiation areas.”

A. 1, 3A. 1, 3 B. 4, 5B. 4, 5 C. 1, 2C. 1, 2 D. 2, 3, 5D. 2, 3, 5 E. 1, 2, 5E. 1, 2, 5

NRC requirements for monitoring call for a likelihood of the individual receiving more than 25% of the MPD and/or having access to areas where the radiation exposure rate could be greater than 1 mSv (100 mrem) per hour at 30 cm from the radioactive sources or adjacent to walls shielding radiation producing equipment, i.e., a "high-radiation area."

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G83.G83. The recommended weekly effective dose equivalent permitted The recommended weekly effective dose equivalent permitted for radiologists under current regulations is:for radiologists under current regulations is:

A. 10 mSvA. 10 mSv B. 50 mSvB. 50 mSv C. 100 mSvC. 100 mSv D. 0.5 mSvD. 0.5 mSv E. 1.0 mSvE. 1.0 mSv

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