Exam 4 Ch 36- Design for Radiation Protection Flashcards
more than ______ are associated w: modern x-ray equipment-
100 individual radiation protection features
many protection features are specific to-
radiography or fluoro
2 radiographic protection features for radiography & fluoroscopy-
tube housing & control panel
tube housing must reduce leakage radiation to-
less than 1 mGA/hr @ distance of 1m
job of tube housing-
protect tube
leakage radiation-
radiation that exits tube at any place other than window/useful beam
control panel protection feature must identify-
-conditions of exposure (kVp & mA indicators)
-positively indicate when tube is energized (visible/audible)
SID Indicator protection feature must-
-be present
-be accurate within 2% of SID
collimation protection feature-
-light-localized variable-aperture rectangular collimation should be provided
-must be within 2% of SID
attenuation of useful x-ray beam must be equal to-
attenuation of protective housing
PBL protection features-
-auto. collimator
-must be accurate to 2% of SID
-no longer required, but is common in new sys.
beam alignment protection features-
IR must be aligned w: center of primary beam
total filtration (inherent + added) must be at least-
-2.5 mm Al above 70 kVp
-1.5 mm Al b/w 50-70 kVp
-.5 mm Al for tubes below 50 kVp
filtration for most diagnostic sys. used today-
have at least 2.5 mm Al
reproducibility should be-
-constant from one exposure to another/reproduce the same image using the same factors multiple times
-shouldn’t exceed 5% intensity change
linearity protection features-
-adjacent mA stations (when time is adjusted to maintain mAs) should produce same intensity
-shouldn’t exceed 10% change in intensity
-refers to the proportional accuracy of the output of the mA station in relation to another
linearity ex-
output of 100 mA station should be double output of 50 mA station
operator shield protection features-
-design of console should prevent exposure by tech. while in room
-exposure button should be fixed
mobile x-ray imaging system protection features-
-lead apron should be assigned to each portable machine
-exposure switch must be on a cord
-useful beam MUST be directed away from tech
length of the cord of the exposure switch on a mobile x-ray imaging sys.-
at least 2 m in length (6ft)
fluoro beam intensity at table top-
-20 mGya/min for each mA of operation @ 80 kVp
-no high level control- 100 mGya/min
-w: high level control- 200 mGya/min
as source to skin distance (SSD) increases, what decreases?
entrance skin exposure
source to skin distance (SSD) must not be-
-stationary fluoro- not less than 38cm (15”)
-mobile fluoro- not less than 30cm (12”)
fluoro Primary Protective barrier-
image intensifier
fluoro total filtration-
no less than 2.5 mm Al equivalent
fluoro collimation-
must be visible on the monitor
fluoro exposure control must be ___ type-
dead-man type (requires constant pressure for it to engage)
fluoro bucky slot cover-
must be 0.25mm Pb equiv. (made of led)
fluoro protective curtain must be-
at least 0.25 mm Pb equiv.
fluoro cumulative timer-
audible signal to denote 5 min. beam on timer
design of protective barriers considerations-
adjacent rooms & floors in rad. facilities
2 types of protective barriers-
primary & secondary
primary protective barriers are-
any wall to which useful beam CAN be directed to is designated a PPB
NCRP report #49-
detail structural design requirements
in fluoro ____ is a primary protective barrier-
image intensifiers
primary protective barriers required size-
-1/16 of an inch of led/led equiv.
-at least 7 ft. high
secondary protective barriers considerations-
-any wall, floor, or ceiling that could have scatter or secondary radiation incident on it
-should never aim primary beam at console
______, ______, & _____ are considered for secondary protective barriers-
scatter, secondary, & leakage radiation
__________ is ALWAYS ONLY behind secondary protective barriers-
operating consoles
secondary protective barriers required size-
-1/32 of an inch of led/led equiv.
-no height requirement
factors affecting barrier thickness (6)-
-distance
-adjacent room occupancy
-control
-workload
-use factor
-kVp
distance from source to barrier decreases-
required thickness increases
adjacent room occupancy increases-
required thickness increases
full adjacent room occupancy-
work areas
frequent adjacent room occupancy examples-
corridors, restrooms, patient rooms
occasional adjacent room occupancy ex-
waiting rooms, stairwells, outside areas, & janitor’s closet
controlled areas occupied by-
mostly by rad. personnel & pts.
controlled areas barriers must reduce exposure rate to-
less than 1 mSv/wk (100 mrem/wk)
uncontrolled areas-
occupied by anyone
uncontrolled area barriers must reduce exposure rate to-
less than
-1 mSv/wk
-20 uSv/wk
-2mrem/wk
workload increases-
barrier thickness increases
use factor-
amt of time beam is energized & directed toward barrier
what do many physicists say ab all barriers-
all barriers are secondary bec useful beam is always intercepted by pt. & IR
kilovolt peak increases-
barrier thickness increases
Radiation detection & measurement-
devices that detect, measure, or both
radiation detection & measurement devices operate in-
pulse or rate mode
pulse mode detects-
presence
rate mode expressed in-
-mGya/hr
-mR/hr
integrate mode-
detects & measures TOTAL amount of intensity of radiation
why are radiation detection & measurement devices called dosimetry?
they use dosimeters
types of dosimeters (4)-
-gas-filled detectors
-schintillation detectors
-TLDs
-OSL detectors
3 types of gas-filled detectors-
-ionization chambers
-proportional counters
-geiger-muller detectors
in gas- filled detectors, the gas in the chamber is maintained-
at constant voltage (voltage changes when hit w: x-radiation)
any electrons liberated by x-radiation are-
detection & measurement
measurement of electrons in gas-filled detectors are proportional to-
radiation intensity
the larger the gas chamber-
the more sensitive the device
pressurized chambers are-
more sensitive
accuracy of gas-filled detectors depends on-
the design of the instrument
voltage in gas chamber will-
increase in stages
voltage in gas chamber increasing in stages, the stages represent-
gas filled stages detected
R- region of recombination-
ions created don’t migrate toward central cathode
Ion chamber Region-
every electron released is attracted to central electrode & collected
Ion chamber regions operate at-
b/w 100-300 volts
ion chambers used for-
detection & calibration
proportion region-
voltage increases, electrons traveling to central electrode will create secondary electrons
proportional region creates-
large electron pulse
proportional detectors can distinguish b/w-
alpha & beta radiation
Geiger Muller Region-
for every single ionization event, nearly all molecules of gas in the chamber are ionized
for sequential detection in GM region-
counters must have an added quenching agent added to filling gas
resolving time-
time required for gas to return to original condition
Continual Discharge Region (CD)-
w: increased voltage, chamber reaches this point
CD region no longer useful for-
detection
continued operation in CD region will-
damage detector
scintillation detector-
certain materials exhibits/emits light under the influence of x-rays
scintillation detectors in CT & Nuclear Medicine-
gamma cameras
amt. of light produced in scintillation detectors is proportional to-
energy absorbed
activator atoms-
thallium
thallium added to-
cesium iodide & sodium iodide
scintillation detectors coated w:-
polished aluminum on all sides except the window
hermetic seal-
aluminum also seals crystals from air & moisture
crystals are hygroscopic-
-absorbs moisture if not sealed
-will swell, crack, & become less accurate
light is incident on a-
photocathode made of cesium, antimony, & bismuth
the number of electrons emitted in scintillation detectors are proportional to-
intensity of light
electrons in scintillation detectors are accelerated to-
dynodes that amplify intensity by secondary electron production
in scintillation, the detectors tube gain is-
dynode gained raised to the # of dynodes in the tube
last element in scintillation detectors-
collecting electrode or collector
scintillation detectors overall-
x-ray or gamma-light-electrons signal
scintillation detectors used in x-ray (3)-
-cesium iodide
-sodium iodide
-gallenium occulosulfide
cesium iodide-
most commonly used
sodium iodide-
commonly used
gallenium occulosulfide mainly in-
fluoro (in cathode intensifiers)
TLDs-
material that glows when heated after irradiation
in a TLD, subsequent light released is measured w:-
photomultiplier
lithium fluoride in TLDs are-
most common
in TLD, calcium fluoride activated w:-
manganese, which makes it more sensitive
TLD can measure doses-
less than 50 uGya (5mrad)
TLDs available-
different size & forms
TLDs are-
-reusable
-responds proportionally
-rugged
-accurate
optical stimulated luminescence detector developed-
in late 1990’s
OSL detector uses-
aluminum oxide
in an OSL, irradiation causes-
electrons to be raised to excited state
in an OSL, laser light causes-
electrons to return to normal when visible light is released
OSL detector minimal reportable dose/precision-
10 uGya (1 mrad)
optical stimulated luminescence detector allows for-
reanalysis
OSL detector-
-exposure condition information
-wide range dynamic
-long term stability
-DOES NOT PROVIDE ANY PROTECTION (acts as snitch)
