Protection Ch 12
Terms in this set (120)
What 2 types of radiation might radiographers be exposed to while fulfilling their profession responsibilities?
List several imaging procedures that increase the radiographer's risk of exposure
general fluoroscopy, interventional procedures that employ HLCF, mobile exams, C-arm fluoroscopy
What does NCRP stand for?
National Council on Radiation Protection and Measurements
What is the NCRP annual occupational effective dose limit?
5 rem (50 mSv)
What is not included in the dose limits?
personal medical and natural background exposure
What is the NCRP lifetime cumulative effective dose limit?
1 rem x age (10 mSv x age)
What is the NCRP non-occupational exposure limit for continuous or frequent exposures?
0.1 rem (1 mSv)
What is the NCRP non-occupational exposure limit for infrequent annual exposure?
0.5 rem (5 mSv)
What is the genetically significant dose (GSD)?
the average annual gonadal equivalent dose to the members of the population who are of childbearing age
What does ALARA stand for?
as low as reasonably achievable
What is another word that can be used in place of ALARA?
What is the best way for radiologists to achieve the ALARA concept?
conscientiously employ appropriate radiation control procedures
What is occupational risk?
the possibility of developing a radiogenic cancer or the induction of a genetic defect as a consequence of the radiation exposure received
How does radiography compare to other professions in occupational risk?
considered reasonably safe
What additional benefit does reducing patient exposure have for radiographers?
it also reduces the radiographer's exposure
During a diagnostic exam, what is the primary source of scattered radiation?
At what angle and distance to the primary x-ray beam is scattered x-ray intensity approx. 1/1000 of the intensity of the primary x-ray beam?
90 degrees, 1 m (3.3 ft)
What poses the greatest occupational hazard in diagnostic radiology?
Why do beam limitation devices reduce scattered radiation?
they restrict the size of the x-ray beam which decreases the number of x-ray photons available to undergo Compton scatter
Who does filtration primarily benefit?
What effect does filtration have on the primary beam?
nonuseful, low-energy photons are removed
What effect does filtration have on the patient?
reduced absorbed dose
What percentage of the radiation that strikes them do lead aprons attenuate?
80% to 90%
What is the lead requirement for clear mobile barriers?
1.5 mm pb eq or 30% lead by weight
As kVp increases a larger percentage of scattered radiation moves in which direction?
forward (more forward-scattered and less side-scattered)
More forward-scattered radiation and less side-scattered radiation due to increased kVp reduces who's exposure?
patient and radiographer
Less mA is required with high-speed image receptor systems, how and why does this affect patient exposure?
patient exposure is reduced due to fewer x-ray photons being available to produce Compton scatter
Why is the need for almost all retakes due to improper technique selection eliminated when using digital imaging?
image contrast and overall brightness can be manipulated after the image is made
List 5 things that reduce radiographer exposure?
digital imaging, high-speed image receptor systems, higher kVp techniques, beam limitation devices, correct processing of radiographic images
What must a pregnant diagnostic imaging staff member do for their pregnancy to be officially recognized?
voluntarily inform her supervisor
What does the health care facility provide to a pregnant diagnostic imaging staff member?
counseling and an additional radiation monitor for the embryo-fetus
Where should a pregnant diagnostic imaging staff member wear the second radiation monitor?
If a pregnant diagnostic imaging staff member wears a lead apron where should the second radiation monitor be worn
under the apron at waist level
What is the NCRP monthly equivalent dose limit for the embryo-fetus?
0.05 rem (0.5 mSv)
How much lead should maternity protective aprons have over their entire length and width?
0.5 mm lead equivalent
Maternity protective aprons have an extra panel that runs transversely across the width of the apron to provide added safety for the embryo-fetus, how much lead is in this panel?
1 mm lead equivalent
What other type of protective aprons can be used during pregnancy?
wraparound aprons of 0.5 mm lead equivalent
How should a pregnant radiographer's work schedule be altered and why?
it does not need to be altered because work schedules are designed to evenly distribute radiation exposure and ALARA guidelines keep exposure to a minimum
What is the NCRP total exposure limit for an entire pregnancy?
0.5 rem (5 mSv)
What are the 3 cardinal rules of radiation protection?
time, distance, shielding
How long is the timer on a fluoroscopic x-ray unit?
When should the radiographer be present in the fluoroscopic room?
only when needed
What is the most effective means of protection from ionizing radiation?
Which law expresses the relationship between distance and the intensity of radiation?
inverse square law
When the distance from the x-ray source is doubled, how is the size of the area irradiated changed?
it is now 4 times larger than the original area
What is the formula for the inverse square law?
I1/I2 = d2^2 / d1^2 (^2 = squared)
What are the most common materials used for radiation shielding?
What are accessory devices such as aprons, gloves, and thyroid shield made from?
What does the effectiveness of shielding materials depend on?
atomic number, density, thickness
Who decides on the exact protection requirements for a particular imaging facility?
a medical physicist
What is the purpose of a primary protective barrier?
to prevent direct, or unscattered, radiation from reaching personnel or members of the public on the other side of the barrier
Where are primary protective barriers located?
perpendicular to the undeflected line of travel of the x-ray beam
What is the typical thickness of a primary protective barrier where the kVP is 130?
1/16 inch lead
How high does the primary protective barrier extend if the x-ray tube is 5 to 7 feet from the wall?
7 feet upward from the floor
What is considered secondary radiation?
radiation that has been deflected from the primary beam (scattered radiation) and leakage radiation
What does a secondary protective barrier protect against?
What is considered a secondary barrier?
any wall or barrier that is never struck by the primary x-ray beam
How much should secondary barriers overlap the primary barrier?
What is the typical thickness of a secondary protective barrier?
1/32 inch lead
What is a control-booth barrier?
a permanent secondary barrier to protect the radiographer required for x-ray rooms housing stationary x-ray equipment
How many times should x-rays scatter before reaching the area behind a control-booth barrier?
minimum of 2
T/F: the tube should never be pointed at the control booth
What is the lead requirement for the window in a control-booth barrier?
1.5 mm lead equivalent or 30% lead by weight
What is the maximum exposure a radiographer should receive behind a control-booth barrier in a week?
100 mrem per week (1 mSv per week)
In actual practice in a well-designed facility, radiographer exposure behind a control-booth barrier should never exceed ___ per week
2 mrem per week (0.02 mSv per week)
How long should the cord to the exposure switch be?
short enough that the radiographer must be completely behind the control-booth barrier to operate it
What is the lead requirement for clear lead-plastic materials used for radiation shields?
30% lead by weight
In addition to control-booth windows, what types of shielding can clear lead-plastic be used for?
overhead x-ray barriers for special procedures and cardiac catheterization
How much protection does clear lead-plastic give when used for overhead x-ray barriers?
0.5 mm lead equivalent protection
What is the disadvantage of increasing the equivalent lead thickness in aprons?
can lead to back problems due to added weight
What metal is used in some protective shielding that has a more probable photoelectric interaction than lead in the lower diagnostic x-ray energy range
What is the required minimum lead equivalent protection of an apron if the kVp is 100?
0.25 mm lead equivalent
What is the required minimum lead equivalent protection of an apron used for fluoroscopy?
0.5 mm lead equivalent
What is the required minimum lead equivalent protection for gloves?
0.25 mm lead equivalent
What is the required minimum lead equivalent protection of neck and thyroid shields?
0.5 mm lead equivalent
What is the required minimum lead equivalent protection of protective eyeglasses?
0.35 mm lead equivalent
What is required to protect the patient and the radiographer from leakage radiation?
a lead-lined metal diagnostic-type protective tube housing
What is the required minimum lead equivalent protection for a fluoroscopy curtain?
0.25 mm lead equivalent
Where should the radiographer stand during a fluoroscopic exam if they are not required near the table?
behind the radiologist or behind the control-booth barrier
What type of protective apron is recommended to be worn during a fluoroscopic exam?
What is a Bucky slot shielding device?
a 0.25 mm lead equivalent shield that automatically covers the Bucky slot opening when the tray is positioned at the foot end of the table
Which procedures cause the highest radiation exposure for diagnostic imaging personnel?
fluoroscopy, mobile radiography, special procedures
How can the radiation exposure be reduced for high radiation procedures such as fluoroscopy, mobile radiography, and special procedures?
scheduling personnel to spend less time in these areas by using a rotational pattern
How many aprons should be assigned to each mobile unit?
1 for each person going
Why do some mobile units have a remote control exposure device?
to allow the radiographer to use distance as a means of radiation protection
How long should the cord to the remote be on a mobile unit?
long enough to let the radiographer stand at least 6 feet from the patient
Where should the radiographer stand during a mobile procedure?
90 degrees to the beam
What is the dose rate for personnel within a meter of the patient during a c-arm procedure?
comparable to that in routine fluoroscopy (several mGy per hour)
During a c-arm procedure, where is the x-ray scatter exposure rate highest?
near the entrance surface of the patient (tube side)
How much difference is there in the amount of scatter on the entrance surface of the patient and the exit surface of the patient?
2 to 3 times more or less (more on tube side, less on IR side)
In c-arm fluoroscopy, where should the x-ray tube be positioned to reduce radiation exposure?
under the table
C-arm fluoroscopes can magnify the image to better visualize smaller body parts, how does this affect radiation exposure?
mA must be increased so exposure is increased
Why do radiation safety techniques become more important in interventional procedures?
extended length of some procedures
What is last-image-hold mode?
the last exposure remains on the monitor so the patient does not have to be exposed again unless new information is needed
How can the radiologist or interventional physician reduce exposure?
shorten the duration of the procedure, take fewer cine images, use pulsed mode, use last-image-hold mode
What is the NCRP annual equivalent dose limit to localized areas of the skin and hands?
50 rem (500 mSv)
When should radiographers stand out to restrain or position a patient?
If a mechanical means of restraint are not available or not feasible, who should do it?
a non-occupationally exposed person such as the patient's relative or a nurse
When should a pregnant woman be allowed to assist holding a patient?
T/F: The doors to the x-ray room can be left open if necessary during a procedure
false (exposures should only be made when the doors are closed)
What are some considerations for radiation barrier design?
mean energy of x-rays, primary or secondary, distance from x-ray source, workload, use factor, occupancy factor, intrinsic shielding, area beyond is controlled or uncontrolled
T/F: Shielding designers should plan conservatively to satisfy current regulatory limits
false (they should plan to satisfy future limits)
What are the 3 categories of radiation sources?
primary, scatter, leakage
What is workload (W)?
the weekly radiation use of a diagnostic x-ray unit
What unit is used to express workload?
mAs per week or mA-min per week
What is use factor (U)?
the portion of beam-on time that the barrier receives radiation during the week (primary beam for a primary barrier, secondary radiation for a secondary barrier)
What is another name for the use factor?
beam direction factor
What is the occupancy factor (T)?
the fraction of the workweek during which the space beyond the barrier is occupied
What is a controlled area?
a region adjacent to a wall of an x-ray room that is used only by occupationally exposed personnel
What is an uncontrolled area?
a hall or corridor that is frequented by the general public
What is the weekly maximum permitted equivalent dose (MPED) for an uncontrolled area?
2 mrem (20 micro Sv)
What is the weekly maximum permitted equivalent dose (MPED) for a controlled area?
100 mrem (1000 micro sV)
How do you calculate barrier shielding requirements?
multiply workload times use factor times occupancy factor and compare answer to a shielding requirement table
What is the limit for leakage radiation?
100 mR/hour at 1 m
When is leakage radiation present?
any time the x-ray tube is on
Which caution sign must be posted if radiation levels cold result in an individual receiving a dose equivalent in excess of 0.005 rem (0.05 mSv) in 1 hour
Caution Radiation Area
Which caution sign must be posted if radiation levels cold result in an individual receiving a dose equivalent in excess of 0.1 rem (1 mSv) in 1 hour
Caution High Radiation Area
Which caution sign must be posted if radiation levels cold result in an individual receiving a dose equivalent in excess of 500 rad (5 Gy) in 1 hour
Grave Danger, Very High Radiation Area
What colors are used for the symbol on a radiation caution sign?
magenta, purple, black
What color is used for the background on a radiation caution sign?