Unit 4 Rad Pro

Monitoring is used to

•ensure occupational radiation exposure levels are kept well below the EfD limit (annual effective dose)

Technologist should be aware of the

various radiation exposure monitoring devices and their functions

Personnel dosimetry monitors the

equivalent dose to any person occupationally exposed on a regular basis to ionizing radiation

•Required when there is a likelihood that an individual will receive more than ___ of the recommended annual dose of 50 mSv

10%

•To keep with ALARA (As Low As Reasonably Achievable) concept, most facilities issue devices when personnel might receive ____ of that dose

1%

Purpose of personnel dosimeters

•Provides indication of working habits and conditions of imaging personnel

•Provides occupational exposure

•Measures the quantity of ionizing radiation exposure

•NOT a method of protection

•During diagnostic radiology, the badge should be worn at _______ facing forward on the anterior side of the individual

collar level

•Consistency of wearing in proper location is responsibility of the

technologist/student

•When wearing a lead apron, the badge should be worn at collar level on the ______ of the apron

outside

•Second monitor with apron (high level studies)

•Inside apron at waist level

•Embryo-fetus monitor

•Inside apron at waist level

•Extremity dosimeter

•When hands are required to be in the primary beam

Control Badges

•Used in calculating monthly occupational doses

•Badge is kept in a distant, radiation-free area and the reading therefore should have a reading of minimal to zero (background radiation)

If the reading is greater than zero, it may have been exposed during transit to company and must be reported to the healthcare facility.

This number must then be subtracted from your total reading to give you your monthly occupational dose

•ALARA I (calendar quarter)

•125 mrem deep dose

•1250 mrem shallow dose

•375 mrem lens of the eye

•1250 mrem to the limbs

•Involves advisement from the RSO

ALARA II (calendar quarter)

•375 mrem deep dose

•3750 mrem shallow dose

•1125 mrem lens of the eye

•3750 mrem to the limbs

•Member of the RSO staff will investigate reasons for high levels

Monitor Characteristics

•Lightweight and easy to carry

•Durable materials to tolerate daily use

•Reliably detect exposures from small to large

•Not affected by outside influences

•Weather

•Humidity

•Mechanical shock

•Inexpensive to purchase

•Easy to maintain

Types of Personnel Monitoring

•Film Badge

•OSL

•TLD

•Pocket Ionization Chamber

•Digital Ionization Dosimeter

                     or

   Direct Ion Storage Dosimeter

Film Badge

•Not used as often

•Uses dental film

•Has aluminum and copper filters that allow conversion to tissue dose

Film Badge Advantages

•Cost efficient

•A few dollars a month

•Provides permanent, legal record

•Durable if dropped

•Can determine if exposure is from scatter or primary radiation

Film Badge Disadvantages

•Temps and humidity can cause inaccurate readings by fogging

•Not recommended to be used more than 1 month

•Not reusable

•Sent out to read

TLD

Thermoluminescent Dosimeter

TLD- Thermoluminescent Dosimeter

•Light free device with crystalline form (powder or small chips) of lithium fluoride that functions as the sensing material

•Energy stored by trapping electrons in crystal lattice

•Crystals are heated, released by the lattice into the conduction band and return to normal state

•Energy is then released in form of visible light which is measured by a TLD analyzer

•The light emitted is directly proportional to exposure

•Creates a graph of exposure called a glow curve

TLD Advantages

•Not effected by humidity or normal temperature changes

•Measures as low as 0.05 mGy

•Exposures below that are recorded as minimal

•Can be worn for 3 months

•Crystals can be reused after reading which can be cost efficient

Has ring option

TLD Disadvantages

•High initial cost and cost of equipment to do reading

•Readings can be lost is not carefully recorded because once energy is released from crystals it cannot be reread

•Records only exposure to area in which it is worn

OSL/ OSLD-
Optically Stimulated Luminescent Dosimeter

•Most common type of device used to monitor occupational exposure

•Best features of all dosimeters

•Contains aluminum oxide layer

OSL? OSLD contain 3 filters

aluminum (least absorption, shallow)

tin (eye)

copper (most absorption, deep)

•Electrons are trapped in the detector. Read out is done when dosimeter is struck by laser light.

•Releases energy in a form of a light.

•Luminescent is proportional to the amount of exposure received

•Exposures below 0.01 mGy are recorded as minimal

•Newer development is a reader called the microStar which reads a special OSL dot called a nanoDot

OSL/ OSLD Advantages

•Lightweight, durable and easy to carry & wear

•Self-contained preloaded packet

•Not affected by heat, moisture or pressure

•Has extended wear up to one year

•Offers complete reanalysis

•Reasonably inexpensive to purchase and maintain

•Has ring option – newest technology

OSL/ OSLD Disadvantages

•Only records exposure to area where it’s worn

•Sent out to be read

•Unless you have a nanoDot version of the OSL/ OSLD

Pocket Ionization Chamber

•Also known as a pocket dosimeter

•Most sensitive

•Uncommon to use in diagnostic radiology

•Resembles a fountain pen

•Contains 2 electrodes, one positive, one negative charged

There are 2 types of pocket ionization chambers

•self reading (contains an electrometer to provide reading)

•non-self reading type (requires an accessory electrometer)

Pocket Ionization Chamber Advantages

•Provides immediate readout

•Compact, easy to carry

•Convenient

Pocket Ionization Chamber Disadvantages

•Fairly expensive

•$150 per unit

•Inaccurate if not read daily

•Can be discharged by a mechanical shock

No permanent legal record

Direct Ion Storage Dosimeter
 (DIS) or digital ionization dosimeter

•Fairly new device

•Provides immediate radiation exposure but can also do long term

Contains ionization chamber that produces and stores electrical charge

DIS readout is obtained by:

•USB

•Wireless connection

•Device wearer’s cellphone app

•Activates the vendor’s software for reading

Direct Ion Storage Dosimeter Advantages

•Lightweight

•Instant access of reports directly to user and stored at facility

•Doesn’t have to be mailed in

•Isn’t easily affected by being dropped or bumped

Direct Ion Storage Dosimeter Disadvantages

•Not effective if not worn properly

Records of Personnel Monitoring
(Radiation Dosimetry reports)

•Purpose is to keep an ongoing tally of employee occupational exposures

•Results must be recorded and maintained to meet state and federal regulations

•Records must be kept permanently by facilities

•Should retrieve records from previous employers and present them to new employer

•Timeframes

•Period of time wearing (monthly for RH)

•Quarterly

•Yearly

•Lifetime

•Deep dose equivalent- DDE

•1cm depth in soft tissue

•Absorbed dose

•Shallow dose equivalent- SDE 

•0.007cm depth in soft tissue

•Dose to external skin

•Eye or Lens dose equivalent- EDE or LDE

•0.3cm depth in the eye

•Exposure to the lens

Committed Dose Equivalent

•Total dose received over a period of time, usually during a 50-year period from an inhaled or ingested radioactive material

•Examples; radon, contaminated food, absorption through the skin, or injected radioisotopes

Specific to a single organ or tissue

500 mSv annual dose limit to

single organs

CDE

Committed Dose Equivalent

CEDE

Committed Effective Dose Equivalent (Ch 4)

Committed Effective Dose Equivalent (Ch 4)

•Applies to long term radiation of individual organs or tissue resulting from inhalation or ingestion of long-lived radioactive material (long decay life)

•Sum of all organs (CDE) x weighting factor for importance (tissue weighting factors)

•Delivered slowly over long period of time from an inhaled or ingested material

•TEDE

Total Effective Dose Equivalent (ch 4) 

Total Effective Dose Equivalent

•Defined by the NRC

•Sum of the deep dose equivalent for external radiation and the committed dose equivalent for internal radiation

•DDE + CDE = TEDE

•Annual dose limit is 50 mSv (whole body) to limit the risk cancer, genetic effects, cataracts, skin damage, sterility…..

Radiation Surveys Instruments

•Detects and measures radiation

•Detects the presence or absence of radiation

Survey Instruments Requirements

•Easy to carry and operated by one person

•Durable enough to withstand normal use

•Reliable

•Should interact with radiation similar to human tissue

•Should be able to detect all types of radiation

•Energy of the radiation should not affect the detector

•Should be cost effective

Gas Filled Radiation Survey Instruments

•Ionization chamber “Cutie Pie”

•Proportional counter

•Geiger Muller (G-M) detector

Ionization Chamber-Type Survey Meter
“Cutie Pie”

•Rate (measures the rate of exposure) and survey meter

•Used for x-ray room installations, measuring scatter from fluoro or CT and calibration

•Can be used to measure exposure rates coming from patients with therapeutic material

•Can be used to measure doses traveling through protective barriers

“Cutie Pie” Advantages

•Measures a wide range of exposures in a few seconds

•Can be used to calibrate x-ray equipment

“Cutie pie” disadvantages

•Without adequate warm up, could cause inaccurate readings

•Large size

•Delicate construction

•Not good with short exposure times

Proportional Counter

•No useful purpose in diagnostic radiology

•Used in laboratories to detect alpha and beta radiation

•Detects small amounts of other types of contamination

Geiger-Muller (GM) Detector

•Used mainly in Nuclear Medicine

•Easily detects areas of contamination and has an audio signal

•Signal increases as radiation is more intense (like how a metal detector responds to metal)

•Reads in counts per minute

Safety Features in Equipment

•On and off switches

•Power equipment down

•Interlocks

•Detents

•Visual- audio monitors

•Timer and audible signal

•Emergency controls

Breakers, stop buttons

Calibration Instruments

•Ionization chambers used in the rate mode can be used to calibrate equipment when used with an electrometer

•Ionization chambers used in the rate mode can be used to calibrate equipment when used with an electrometer

•X-ray output

•Reproducibility and linearity of output

•Timer accuracy

•Half value layer

•Beam quality

•Entrance exposures for fluoro

•With a calibrated parallel plate chamber it could check mammo equipment

•Examples:

•Collimation accuracy- 2%

•SID indication- 2%

•PBL- 2%

•Variation in exposure- 5%

Equipment Surveys

•Surveys must be done by RSO and in writing

•Keep permanently and indicate if a resurvey is necessary and if so when

•Safety surveys are done in conjunction with preventative maintenance

•Performance surveys are done annually

Equipment Surveys Examples

•Timer accuracy

•Exposure reproducibility

•kVp test

•Linearity of mAs

•Tube stability

•Beam limiting device

•Timer

•Primary barrier

•kVp and mAs indication

•High levels control

Exposure rate limits