MI:120 Unit 4: Radiation Monitoring

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

ALARA Investigations: 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

Deep dose equivalent- DDE

-1cm depth in soft tissue -Absorbed dose

ALARA Investigations: 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

Film Badge Disadvantages

-Accuracy is limited to +/- 20% -Temps and humidity can cause inaccurate readings by fogging -Not recommended to be used more than 1 month -Not reusable -Reading can take a longer time because badge has be sent out to be read

Ionization Chamber-Type Survey Meter "Cutie Pie" Disadvantages

-Adequate warm up -Large size -Delicate construction -Not good with short exposure times

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 -Can be Self-Reading and Non-Self Reading

OSL- Optically Stimulated Luminescent Dosimeter

-Best features of film badge and TLD -Detector is aluminum oxide -Contains 3 filters: aluminum (least absorption, shallow), tin (eye) and copper (most absorption, deep) -Electrons are trapped in the badge. 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

Committed Dose Equivalent

-CDE -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

Committed Effective Dose Equivalent

-CEDE -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

Film Badge Advantages

-Cost efficient -A few dollars a month -Provides permanent, legal record -Detects different types of radiation and can discriminate between types -Measures as low as 0.1mGy -Doses below that are recorded as minimal -Durable if dropped -Can determine if exposure is from scatter or primary radiation

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

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

Digital Ionization Dosimeter

-Fairly new device -Provides immediate radiation exposure but can also do long term -Looks like a flash drive -Contains ionization chamber that produces and stores electrical charge -Connects to a computer to provide a readout -Activates the vendor's software for reading

Types of Personnel Monitoring

-Film Badge -OSL -TLD -Pocket Ionization Chamber -Digital Ionization Dosimeter

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

Gas Filled Radiation Survey Instrument

-Ionization chamber "cutie pie" -Proportional counter -Geiger Muller (G-M) detector

Calibration Instruments

-Ionization chambers used in the rate mode can be used to calibrate equipment when used with an electrometer -Used by medical physicist for standard measurements required by state, federal, and accreditation organizations for x-ray and fluoro units. Examples: -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%

TLD- Thermoluminescent Dosimeter

-Light free device with crystalline form of lithium fluoride that functions as the sensing material -Energy stored by trapping electrons in crystal lattice -Crystals are heated and the stored energy is released in form of visible light which is measured by a photomultiplier tube. The light emitted is directly proportional to exposure

Digital Ionization Dosimeter Advantages

-Lightweight -Instant reports -Doesn't have to be mailed in -Isn't easily affected by being dropped or bumped

Radiation Badge Monitor Characteristics

-Lightweight and easy to carry -Durable to tolerate normal use -Reliably detect exposures from small to large -Not effected by outside influences -Weather -Humidity -Mechanical shock -Inexpensive to purchase and maintain -Easy to maintain

OSL Advantages

-Lightweight, durable and easy to carry -Self-contained preloaded packet -Not affected by heat, moisture or pressure -Has extended wear up to one year, but recommended for a 2 month period -Offers complete reanalysis -Reasonably inexpensive to purchase and maintain

Ionization Chamber-Type Survey Meter "Cutie Pie" Advantages

-Measures a wide range of exposures in a few seconds -Can be used to calibrate x-ray equipment

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

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

Film Badge

-Not used as often -Records whole body radiation at low rate over a long period of time -Uses dental film -Filters low energy x-ray, gamma and beta -Has aluminum and copper filters that allow conversion to tissue dose

Safety Features in Equipment

-On and off switches -Interlocks -Visual- audio monitors -Emergency controls

OSL Disadvantages

-Only records exposure to area where worn -Has to be sent out to be read, so some time elapses before you receive your reading -Unless you have a nanoDot version of the OSL

Timeframes

-Period of time wearing (monthly for RH) -Quarterly -Yearly -Lifetime

Pocket Ionization Chamber Advantages

-Provides immediate readout -Compact, easy to carry -Convenient

Purpose of Radiation Badges

-Provides working habits and conditions of imaging personnel -Provides occupational exposure -Measures the quantity of ionizing radiation exposure -Not a method of protection

Records of Personnel Monitoring

-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

Ionization Chamber-Type Survey Meter "Cutie Pie"

-Rate (measures the rate of exposure) and survey meter -Used to measure radiation in an area such as a fluoro room, radioisotope storage areas, or patient's with radioactive sources -Can be used to measure doses traveling through barriers

Requirements of Radiation Badges

-Required when there is a likelihood that an individual will receive more than one- quarter (~12.5 mSv) the recommended annual dose of 50 mSv -To keep with ALARA concept most facilities issue devices when personnel might receive 1% of that dose

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

Total Effective Dose Equivalent

-TEDE -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.....

Requirements of Personnel Monitoring

-Timeframes -Doses Like: -Deep dose equivalent- DDE -Shallow dose equivalent- SDE -Eye or Lens dose equivalent- EDE or LDE

Equipment Surveys Examples

-Timer accuracy -Exposure reproducibility -kVp test -Linearity of mAs -Tube stability -Beam limiting deviceTimer -Primary barrier -kVp and mAs indication -High levels control -Exposure rate limits

Control Badges

-Used in calculating monthly occupational doses -Badge is kept in a distant room and the reading (which consists of background radiation) is subtracted from your total reading to give you your monthly occupational dose

Geiger-Muller (G-M) Detector

-Used mainly in Nuclear Medicine -Easily detects areas of contamination and has an audio signal -Signal increases as radiation is more intense (similar to how a metal detector responds to metal) -Reads in counts per minute

Placement of Radiation Badges

-Worn with proper side forward -During diagnostic radiology, the badge should be worn at collar level on the anterior side of the individual -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 outside of the apron -Second monitor with apron (high level studies) -Embryo-fetus monitor -Extremity dosimeter

Emergency controls

Breakers, stop buttons

Total Effective Dose Equivalent Formula

DDE + CDE = TEDE

Interlocks

Detents

Embryo-fetus monitor

Inside apron at waist level

Second monitor with apron (high level studies)

Inside apron at waist level

Digital Ionization Dosimeter Disadvantages

Not effective if not worn properly

On and off switches

Power equipment down

Visual- audio monitors

Timer and audible signal

Extremity dosimeter

When hands are required to be in the primary beam

Self-Reading Pocket Ionization Chamber

contains an electrometer to provide reading

Non-Self Reading Pocket Ionization Chamber

requires an accessory electrometer