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What is the annual limit for occupationally exposed personnel?
5 rem or 50 mSv
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Effective Dose (EfD) unit of measurement is the:
rem or Sv
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Cumulative Dose (CumEfD) unit of measurement is calculated by what formula?
CumEfD = years x 1rem
(1rem = 10mSv)
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Where are you most likely to reach your CumEfD, if at all?
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Annual Dose Limits for:
Total Dose
Eye
Thyroid gland
an individual organ
skin or extremity
minor (<18)
embryo/fetus
medical muggles (haha)
unrestricted areas
- Total Dose: 20mS/2rem (ICRP) or 50ms/5rem (NCRP)
- Eye: 150mS/15rem
- Thyroid Gland: 300mS/30rem
- an individual organ: 500mS/50rem
- skin or extremity: 500mS/50rem
- minor (<18): 10% of adult
- embryo/fetus: 5mS/.5rem (over 9 months)
- medical muggles: 1 per year
- unrestricted areas: 0.02mS/hr = .002rem/hr
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ALARA concept:
holds that exposure should be kept "As Low As Reasonably Achievable"
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What are the three main factors that can help us to maintain the ALARA concept?
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At a distance of 1 meter, the scattered x-ray intensity is generally______________________ of the intensity of the primary beam.
approximately 1/1000
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If you must be standing near the patient during the exposure, where should you stand (in relation to the patient)?
at the head or foot, but not at the side, if possible
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If Positive Beam Limitation is used, it must be accurate to __________ of the SID.
within 2%
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What does filtration do, and how does it affect the patient?
- it increases the overall average energy of the beam
- reduces patient dose
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How do higher energies cause the radiation to travel?
in a more forward motion toward the receptor
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Is more or less technique needed with high-speed receptor systems?
less (decreasing patient and personnel doses)
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Why are repeats in radiography significantly decreasing in digital imaging?
the greater abilities of the digital equipment to manipulate the images with processing
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What must a pregnant employee do for the hospital to officially recognize the pregnancy?
sign a voluntary declaration of pregnancy
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Pregnancy aprons consist of an overall _____lead equivalency and an extra _____ lead equivalency protective panel that runs transversely across the width of the apron.
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What is the inverse square law?
- when you double you distance from the site of radiation (scatter from patient), you decrease the intensity by a factor of 4.
- ex. triple the distance, decrease by a factor of 9
- ex. quadruple the distance, decrease by a factor of 16
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What is the lead equivalency of the lead curtain?
.25 mm
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What are the two main types of protective barriers?
- primary barrier (wall that is actually hit by primary radiation)
- secondary barrier (walls that are not hit directly by primary radiation)
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What is the lead equivalency necessary for the primary barrier? for the secondary barrier?
- primary: 1/16
- secondary: 1/32
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If you increase the mAs, does the dose to the tech increase or decrease?
increase (number of x-rays increases, therefore number of photons received by tech increase)
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If you increase the kVp, does the dose to the tech increase or decrease?
increase (energy of scatter photons produced by patient increases, therefore dose to personnel increases)
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What does the bucky slot cover do and what is its lead equivalency?
- it blocks radiation coming out of the bucky hole
- .25 mm
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How long is the x-ray cord extension on a portable machine?
6 feet
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Which side is safer for the tech to stand on if possible during the use of the C-arm fluoroscope?
the side of the image intensifier where there is low scattered radiation as opposed to the side of the x-ray tube where there is high backscatter radiation
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Essentially the weighted time during the week the unit is actually delivering radiation:
Workload
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Intensity of radiation related to distance
- Inverse Square Law
- ex. doubling distance decreases intensity received by a factor of 4
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an area where non radiation workers may be present:
Uncontrolled area
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an area where radiation workers are present:
Controlled area
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Used to modify the shielding requirement for a particular barrier by taking into account the fraction of the x-ray unit's workload for which there is occupancy beyond that barrier:
Occupancy Factor
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The proportional amount of time during which the x-ray beam is energized or directed toward a particular barrier:
Use Factor
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Tube housing leakage much be kept below:
100mR/hr at 1 meter from the tube housing
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