MI120 unit 4 Flashcards
requirements for radiation monitoring
when there is a likelihood that an individual will receive more than 10%, the recommended dose annual dose is 50 msv
how do facilities keep up with ALARA
facilities offer devices when personnel might receive 1% of that dose
what is the purpose of radiation monitoring
-provides working habits and conditions of imaging personnel
-occupational exposure
-measures the quantity of ionizing radiation exposure
-mot a method of protection
Placement
-must be worn with proper side forward
-during diagnostic radiology, the badge should be word at collar level
-consistency of wearing in proper location is up to the radiologist/student
-bade must be worn outside the apron
-second monitoring with apron is inside apron at waist level
embryo fetus must be at waist level
extremity dosimeter
when hands are required to be in primary beam
control badge
used to calculate occupational doses
-badge is kept in a distant room and the reading is minimal to zero from your total reading to give you your monthly occupational dose
ALARA I
-125 mrem deep dose
-1250 mrem shallow dose
-375 mrem lens of the eye
-1250 mrem to the limbs
-advisement from RSO
monitor characteristics
-lightweight and easy to carry
-durable to tolerate normal use
-reliably detetct exposures from small to large
-not effected by outside influences
-inexpensive
-easy to maintain
ALARA II
-375 mrem deep dose
-3750 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
-not used often
-uses dental film
-has aluminum and copper filters that allows conversion to tissue dose
advantages of film badge
-cost effective
-provides permanent legal record
-durable if dropped
-can determine if exposure is from scatter or primary radiation
disadvantages of film badge
-temps and humidity can causes inaccurate readings by fogging
-not recommended to be used more than 1 month
-not reusable
-sent out to read
advantages of TLD
-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
-crystal can be reused after reading
TLD (thermoluminescent dosimeter)
-light free device with crystalline form of lithium fluoride that function as the sensing material
-energy stored by trapping electrons in crystal lattice
-energy is released in form of visible light which is measured by a TLD analyzer
-the light emitted is directly proportional to the exposure
-a graph of exposure is created called a glow curve
disadvantages of TLD
high initial cost and cost of equipment to do reading
-can be lost if 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 stimultaed luminescent dosimeter)
-most common type used
-detector is aluminum oxide
-contains : aluminum (least absorbed), tin (eye), and copper (most absorbed)
-electrons are trapped in badge
-newer development is a reader called the microstar which reads special OSL dot called a nanodot
advantages of OSL
-lightweight, dural and easy to carry
-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
pocket ionization chamber
AKA a pocket dosimeter
-most sensitive
-uncommon to use in diagnostic radiology
-resembles a fountain pen
-contains 2 electrodes (positive and negative
advantages of pocket ionization chambers
-provides immediate readout
-compact, easy to carry
-convenient
types of pockets ionization chamber
self reading- contains an electrometer to provide reading
-non-self reading type- requires an accessory electrometer
disadvantages of the pocket ionizing chamber
-fairly expensive ($150)
-inaccurate if not read daily
-can be discharged by mechanical shock
-no permanent legal record
direct ion storage dosimeter
-fairly new device
-provides immediate radiation exposure but can also do longterm
-contains an ionization chamber that produces and stores electrical charge
-connects to a computer to provide a readout
advantages of direct ion storage dosimeter
-lightweight
-instant reports
-doesnt have to be mailed in
-stable
records of personnel monitoring
-purpose is to keep an ongoing tally of employee occupational exposure
-results must be recorded an maintained to meet state and federal regulations
-records must be kept permanently
-should retrieve records from employers and present them to new employer
disadvantages of direct ion storage dosimeter
-not effective if not worn properly
timeframes
-period of time wearing: quarterly, yearly, lifetime
disadvantage of OSL
only record exposure to area where worn
-has to be sent out to read
-unless you have the nanoDot version of the OSL
timeframes
-period of time wearing: quarterly, yearly, lifetime
doses
-deep dose equivalent- DDE
-1 cm depth in soft tissue, absorbed dose
-shallow dose equivalent- SDE
-0.007 cm depth in soft tissue, skin dose
eye or lens dose equivalent- EDE or LDE
-0.3 depth in the eye, exposure to the lens
committed dose equivalent (CDE)
total dose equivalent received over a period of time, usually during a 50 year period from inhaled or ingested radioactive material
-500 mSv annual dose limit to singe 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 organ (CDE) X weighting factor for importance (tissue weighting factors)
0delivered slowly over long period of time from an inhaled or ingested material
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, etc
radiation survey instruments
-detects and measures radiation
-detects the presence of absence of radiation
radiation survey requirements
easy to carry, 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, cost effective
gas filled survey instruments
-ionization chamber “cutie pie”
-rate (measures the rate of exposure) and survey meter
-used for xray room installation, measuring scatter from fluoro and CT
-can be used to measure exposure rates coming from the therapeutic material of patient
-can be used to measure doses traveling through a protective barrier
advantages of cutie pie
measures a wide range of exposures in a few seconds
-can be used to calibrate xray equipment
disadvantages of cutie pie
-adequate warm up
-large size
-delicate construction
-not good with short exposure times
proportional counter
not useful purpose in diagnostic radiology
-used in lab to detect alpha and beta radiation
-detects small amounts of other contamination
geiger mullar detector
used mainly in nuclear medicine
-easily detects areas of contamination and has an audio signal
-signal increases as radiation is more intense
-reads in counts per minute
safety features
on and off switches- power equipment down
-interlocks (detents)
-visual /audio- timer and audible signals
-emergency controls- breakers, stop buttons
-calibrations
calibrations
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 xray and fluoro
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 survey are done in conjunctions with preventative maintenance
-performance surveys done annually
