radiation protection chapter 23 biological effects of radiations high doses lethal with whole body...

Radiation ProtectionRadiation Protection

Chapter 23Chapter 23

Radiation Dosimetry Terms

Exposure Air kerma Entrance skin exposure (ESE) Entrance air kerma Radiation absorbed dose Dose equivalent (H) Effective dose equivalent (HE or EDE)

Radiation exposure is Radiation exposure is measuredmeasured in Roentgens (R) - in Roentgens (R) - convenient, or Coulomb/kg ,convenient, or Coulomb/kg , Not what we want to knowNot what we want to know

Radiation dose Radiation dose relates to patient riskrelates to patient risk but cannot be but cannot be measured - dose must be measured - dose must be calculated calculated

Dose is calculated based on: entrance exposure, Dose is calculated based on: entrance exposure, x-ray beam energy and tissue thickness x-ray beam energy and tissue thickness and type

What is radiation exposure and What is radiation exposure and dose?dose?

Radiation exposure and Radiation exposure and dosedose

The absorption of x-ray photons results in the deposition of energy in the tissue. The energy deposited per unit mass of tissue is the radiation absorbed dose. The traditional unit of measurement of absorbed dose is the rad (radiation absorbed dose). Defined as 100 erg/g.

SI units: 100 rads = 1 Gray = 1 Joule / kg.


Equivalent dose takes into acount the biological effectiveness of the radiation. It is expressed in rems (rad equivalent man) and is equal to the dose in rads times a radiation weighting factor wr. For x-rays, wr = 1. Therefore equivalent dose in rems is exactly equal to the dose in rads, i.e. 1 rad = 1 rem.

SI units: 100 rem = 1 Sievert (Sv)


Effective dose equivalent is the sum of equivalent doses in all tissues or organs irradiated, each multiplied by

the appropriate tissue weighting factor.

H = Σ wT x HT

Unit is the rem.

SI units: 100 rem = 1 Sievert (Sv)

Radiation exposure and Radiation exposure and dosedoseIf a radiation exposure involves less than the

entire body (such as in mammography, chest x-ray, etc), the effective dose is defined as the equivalent dose that, if delivered to the whole body, would produce the same risk to the patient as the given exposure.

For example if ½ of the body receives 100 mrem the effective dose would be 50 mrem.


some wT values:

gonads = 0.2 red bone marrow, lung, colon, stomach

= 0.12breast, bladder, liver,

esophagus,thyroid = 0.05skin = 0.01

Quantities and Radiation Quantities and Radiation UnitsUnits Exposure - RoentgenExposure - Roentgen

measurement of ionization in airmeasurement of ionization in air exposureexposure

Absorbed Dose – rad, Gray (1 Gray = 100 rad)Absorbed Dose – rad, Gray (1 Gray = 100 rad) 1 rad = 1 cGy1 rad = 1 cGy amount of energy deposited per gramamount of energy deposited per gram

Equivalent Dose – rem, Sievert (1 Sv = 100 Equivalent Dose – rem, Sievert (1 Sv = 100 rem)rem) 1 mrem = 10 microSv1 mrem = 10 microSv radiation protectionradiation protection

Effective Dose – rem, SievertEffective Dose – rem, Sievert

Sources of Exposure to US Sources of Exposure to US PopulationPopulation

Annual average total Annual average total effective dose:effective dose: 3.6 mSv or ~10 3.6 mSv or ~10

microSv/daymicroSv/day 360 mrem or ~ 1 mrem/day360 mrem or ~ 1 mrem/day

Most of dose fromMost of dose from RadonRadon Internal emittersInternal emitters Terrestrial radioactivityTerrestrial radioactivity Cosmic raysCosmic rays


Radon Radon 2 mSv or 200 mrem/yr2 mSv or 200 mrem/yr radioactive noble gasradioactive noble gas daughter of radium-226daughter of radium-226 alpha emitteralpha emitter 4 day half-life4 day half-life

Daughters of radonDaughters of radon also radioactivealso radioactive attach to dustattach to dust irradiate bronchial irradiate bronchial

mucosamucosa 15 - 20% of lung cancers15 - 20% of lung cancers


Internal emittersInternal emitters 0.4 mSv or 40 mrem/yr0.4 mSv or 40 mrem/yr K-40 primary sourceK-40 primary source present in musclepresent in muscle male dose > female male dose > female

dosedose


Terrestrial emittersTerrestrial emitters 0.28 mSv or 28 0.28 mSv or 28

mrem/yrmrem/yr long-lived natural long-lived natural

emittersemitters uranium, radium, uranium, radium,

thorium, C-14thorium, C-14


Cosmic raysCosmic rays 0.27 mSv or 27 mrem/yr0.27 mSv or 27 mrem/yr high energy protons, x-rays, high energy protons, x-rays,

etcetc > .05% reach sea level> .05% reach sea level air attenuation equivalent to air attenuation equivalent to

~34 feet of water~34 feet of water AltitudeAltitude

dose doubles per 1500 mdose doubles per 1500 m @ 40,000 feet ~ 0.5 mrem/hr@ 40,000 feet ~ 0.5 mrem/hr 5 hour flight at 40,000’ 5 hour flight at 40,000’

results in dose 0.025 mSv or results in dose 0.025 mSv or 2.5 mrem or 25 microSv 2.5 mrem or 25 microSv


Enhanced natural sourcesEnhanced natural sources smoking smoking

13 mSv or 1.3 rem13 mSv or 1.3 rem medical x-raysmedical x-rays

0.39 mSv or 39 mrem0.39 mSv or 39 mrem nuclear medicinenuclear medicine

0.14 mSv or 14 mrem0.14 mSv or 14 mrem falloutfallout

0.01 mSv or 1 mrem0.01 mSv or 1 mrem nuclear powernuclear power

<<0.01 mSv or < 0.05<<0.01 mSv or < 0.05

Average Annual Occupational Average Annual Occupational Effective Dose EquivalentEffective Dose Equivalent

Personnel DosimetryPersonnel Dosimetry

Film badgeFilm badge metal filters (lead, copper, aluminum) used to identify metal filters (lead, copper, aluminum) used to identify

photon energy photon energy open window used to measure betasopen window used to measure betas range 100 microGy (10 mrad) to 15 Gy (1500 rad)range 100 microGy (10 mrad) to 15 Gy (1500 rad) provide deep and shallow (skin) doseprovide deep and shallow (skin) dose

Optically Stimulated Luminescent (OSL)Optically Stimulated Luminescent (OSL) trapped electrons, which are proportional to dose, read trapped electrons, which are proportional to dose, read

out using laserout using laser Thermoluminescent Dosimeter (TDL)Thermoluminescent Dosimeter (TDL)

trapped electrons, which are proportional to dose, read trapped electrons, which are proportional to dose, read out using heatout using heat

small size small size

Exposure ControlExposure Control

TimeTime DistanceDistance

inverse square lawinverse square law ShieldingShielding

lead apron of 0.5 mm lead equivalent lead apron of 0.5 mm lead equivalent attenuates ~ 90% of incident radiationattenuates ~ 90% of incident radiation

X-ray Room ShieldingX-ray Room Shielding

X-ray Room Shielding X-ray Room Shielding Terms to RememberTerms to Remember

Workload, W (mA-minutes/week)Workload, W (mA-minutes/week) amount of x-rays produced per weekamount of x-rays produced per week

Use Factor, U Use Factor, U fraction of time radiation is directed at a particular fraction of time radiation is directed at a particular

barrier (wall) barrier (wall) 0 to 1 0 to 1

Occupancy Factor, TOccupancy Factor, T fraction of time per week an individual spends in an fraction of time per week an individual spends in an

adjacent area, adjacent area, 0 to 10 to 1 T = 1 for office; T = 1/16 for hallwayT = 1 for office; T = 1/16 for hallway

DistanceDistance

X-ray Room Shielding X-ray Room Shielding Terms to RememberTerms to Remember

Control AreaControl Area access controlled, individuals are access controlled, individuals are

monitored, trained in radiation protectionmonitored, trained in radiation protection exposure to personnel limited to 50 mSv or exposure to personnel limited to 50 mSv or

5 rem/year5 rem/year Unrestricted AreaUnrestricted Area

accessible by the general publicaccessible by the general public exposure limited to 1 mSv or 100 exposure limited to 1 mSv or 100

mrem/yearmrem/year

Maximum Permissible Annual Maximum Permissible Annual Dose LimitsDose Limits

ALARAALARAAs Low As Reasonably As Low As Reasonably

AchievableAchievable dose limits to workers and public are dose limits to workers and public are

regarded as upper limits rather than regarded as upper limits rather than a acceptable dosesa acceptable doses

radiation safety programs in radiation safety programs in hospitals operate such that doses are hospitals operate such that doses are one tenth of annual dose limitsone tenth of annual dose limits

personnel doses reviewed quarterlypersonnel doses reviewed quarterly

Advisory BodiesAdvisory Bodies National Council on Radiation Protection National Council on Radiation Protection

(NCRP)(NCRP) publishes monographs containing publishes monographs containing

recommendations on radiation health issuesrecommendations on radiation health issues monographs serve as reference documents monographs serve as reference documents

from which regulations are developedfrom which regulations are developed International Commission on Radiation International Commission on Radiation

Protection (ICRP)Protection (ICRP) international body similar to NCRPinternational body similar to NCRP

Regulatory AgenciesRegulatory Agencies

US Nuclear Regulatory Agency (USNRC)US Nuclear Regulatory Agency (USNRC) regulates byproduct materials, and accelerator regulates byproduct materials, and accelerator

produced materials, etcproduced materials, etc specifies dose limitsspecifies dose limits agreement states (~37) assume regulatory agreement states (~37) assume regulatory

authority of the NRCauthority of the NRC Food and Drug Agency (FDA)Food and Drug Agency (FDA)

regulates pharmaceuticals, all x-ray equipment, regulates pharmaceuticals, all x-ray equipment, certifies mammography facilitiescertifies mammography facilities

Department of Transportation DOTDepartment of Transportation DOT regulates transportation of radioactive materialsregulates transportation of radioactive materials

Sum of Internal and External Sum of Internal and External DosesDoses

Internal dosesInternal doses continues after ingestion until decay or continues after ingestion until decay or

excretionexcretion committed dose equivalent is dose to tissue or committed dose equivalent is dose to tissue or

organ over 50 yearsorgan over 50 years committed effective dose equivalent (CEDE) is committed effective dose equivalent (CEDE) is

sum of dose equivalent to organ times a tissue sum of dose equivalent to organ times a tissue weighting factorweighting factor

External dosesExternal doses deep dose as indicated by personnel dosimeterdeep dose as indicated by personnel dosimeter

Total effective dose equivalent (TEDE)Total effective dose equivalent (TEDE) sum of internal and external dosessum of internal and external doses

1. Define the following quantities and give the units of each: a. Absorbed Doseb. Dose Equivalent c. Effective Dose Equivalent

2. What is the annual, average per capita total effective dose equivalent to the US

population and what are the sources of this exposure? 3. What is the total effective dose for a 5 hour transcontinental flight? 4. What is the average, annual occupational exposure for radiologists and x-ray

technologists? 5. If the distance from a point source of radiation is doubled, how much does the

exposure rate change? 6. What fraction of a diagnostic beam incident on a patient is scattered at 90 degrees

one meter from the patient? 7. What sources of radiation must be considered when designing the shielding for a

diagnostic x-ray room? 8. Define workload, use factor, occupancy factor, primary barrier and secondary

barrier. 9. The principle that radiation doses should be kept to the lowest level consistent

with cost and other factors is known as: a. de minimus dose b. ALARA c. dose threshold d. MPD (maximum permissible dose) e. EDE (Effective Dose Equivalent)

10. The advisory group that recommends standards for radiation protection in the United States is the: a. NRC (Nuclear Regulatory Commission) b. DOE (Department of Energy) c. ICRP (International Council on Radiation Protection) d. NCRP (National Council on Radiation Protection)e. EPA (Environmental Protection Agency)

11. The EDE limit in mSv/year for members of the public exposed frequently or continuously to radiation is: a. 100 b. 10c. 1d. 0.1e. 0.01

12. In limiting exposures to members of the public, the following sources are not included (more than one answer may be correct): a. terrestrial background b. medical x-rays c. nuclear medicine procedures c. radon in the home e. cosmic rays

13. Match the definitions a-c with the expressions 1-3. a. fraction of time beam is directed toward location 1. workloadb. fraction of time people are present in location 2. use factor c. mA-min/week 3. occupancy factor

14. The walls of a room require 2mm of lead. If the workload of the x-ray unit in theroom is doubled, how much lead in mm must be added to the walls? (HVL is 0.5 mm of Pb)a. none b. 0.5 mm of Pb c. 1 mm of Pbd. 2 mm of Pbe. 4 mm of Pb

radiation protection chapter 23 biological effects of radiations high doses lethal with whole body...

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