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Radiation Protection Of Health Care Workers
Kyle Thornton RADL 70
Principles Of Radiation Protection
Technologists should never hold patients Technologists should never be exposed to
the primary beam except for their own medical diagnosis
No one person should ever routinely hold patients
The person designated to hold patients should remain at right angles to that person and wear lead protective garments
The Technologist’s Mantra Of Radiation Protection
Time Distance Shielding
Time
Reduce the amount of time spent near the source
Time and radiation exposure are directly proportional
If time doubles, radiation exposure doubles Formula: t1/t2 = I1/I2
Distance
The most effective means of reducing radiation exposure Inverse square law I1/I2 = D2²/D1² If distance is halved, intensity increases by 4 times If distance is doubled, intensity decreases by 1/4 As distance increases, radiation intensity decreases
As distance decreases, radiation intensity increases The numerical change is squared
Applications Of The Inverse Square Law
Solve the following problems: A radiographer receives 10mrem at 1 foot. What is the
exposure at 2 feet?
2.5mrem A radiographer receives 10mrem at 1 foot. How far back does
the radiographer have to step to reduce the exposure to 5mrem?
1.41 feet
Shielding
Structural barriers Mobile shields Lead apparel Lead is the material preferred for shielding High atomic number - 82 Majority of scattered photons are absorbed
Types Of Barriers
Fixed barriers Primary barrier
Wall or other area struck by primary beam Must be at least seven feet high
Secondary barrier Absorbs scatter radiation Beam cannot be directed toward this Control booth is generally thought of as secondary
barrier except in California Ceiling always is a secondary barrier
Lead Aprons
Made of powdered lead incorporated into rubber or vinyl
Must be .25mm lead equivalent at 100 kVp if used as secondary barrier
Must be .5mm lead equivalent if used as primary barrier
Other Lead Apparel
Gloves Shall be at least .25mm lead equivalent Also available as sterile gloves
Very thin, not as attenuating as regular lead gloves Thyroid Shields
Should definitely be used Thyroid is very sensitive to radiation exposure
Goggles Clear lenses Shall be at least .35mm lead equivalent
Mobile Shields
Can be moved Used in angiography, surgery
Structural ShieldingWhat Is It Used For?
Primary and secondary radiation Controlled/Restricted areas Uncontrolled/Unrestricted areas Leakage radiation
Controlled/Restricted Area
An area with an active source of radiation Limited access Maximum weekly dose is 100mrem
Uncontrolled/Unrestricted Area
Areas accessible to general public Radiation exposure cannot exceed
2mrem/week
Determining Barrier Thickness
Distance - D Use - U Workload - W Occupancy - T
DUWT - rhymes with newt
Distance
Distance from source to barrier Inverse square law applies
Use Factor
Weekly beam-on time toward a particular barrier Full use - 1
floors, walls, ceilings exposed routinely to primary beam Partial use - 1/4
Doors, walls, floors of dental equipment not routinely exposed to primary beam
Occasional use - 1/16 ceilings not routinely exposed
Workload Factor
mA minutes or seconds per week Total radiation output time during the week
Occupancy Factor - T
How the area on the other side of the protective barrier will be used
Full - 1 Areas of heavy use
Partial - 1/4 Areas of some use
Occasional - 1/16 Areas of very limited use
Calculation For Barrier Thickness
Kux = P(dpri)² or W(U)(T) WUT
P = weekly design exposure rate in Roentgens
dpri = distance from source to person being protected
W - workload in mA minutes/week U - use factor for that wall T - occupancy factor of area being evaluated
Protective Tube Housing
Metal diagnostic-type protective tube housing is required to prevent leakage and off-focus radiation
Leakage radiation cannot exceed 100 mR/hr at a distance of 1 meter from x-ray tube
Protection During Fluoroscopy
There must be a protective curtain or sliding panel of .25mm lead equivalent between patient and technologist
There must be a bucky slot shielding device of .25mm lead equivalent which slides into place when the bucky tray is placed at the foot of the table
Fluoroscopic exposure monitors and rotational scheduling are helpful, but are optional
The Pregnant Technologist
Pregnant technologists should be able to perform all duties
A technologist must inform her supervisor in writing of her pregnancy
The technologist can wear an additional monitor Should be worn beneath the lead apron at waist level
Question: What is the monthly dose limit for the pregnant technologist?
Question: What is the dose limit during the entire gestational period?
Protection During Mobile Radiography And Fluoroscopic Examinations
Protective apparel should be worn If possible, mobile protective barriers should be used Exposure switch of the portable unit must allow operator a 6 foot
distance from tube, patient, or useful beam Radiographer should stand at 90 to the scattering object
This is area of least scatter Cineradiography is the area of most radiation exposure Monitors should have last image hold
Personnel Monitoring
Generally accomplished through personnel dosimetry
Anyone receiving 10% or more of TEDE must be monitored
Personnel Dosimeters
Desirable characteristics Should be lightweight, durable, and reliable Should be inexpensive
Types of personnel dosimeters Film badge Pocket ionization chambers Thermoluminescent dosimeters (TLD)
Film Badge Most widely used and most economical Consists of three parts:
Plastic film holder Metal filters Film packet
Can read x, gamma, and beta radiation Accurate from 10mrem - 500rem Developed and read by densitometer A certain density value equals a certain level of radiation Read with a control badge Results generally sent as a printout
Advantages And Disadvantages Of The Film Badge
Lightweight, durable, portable Cost efficient Permanent legal record Can differentiate between
scatter and primary beam Can discriminate between x,
gamma, and beta radiation Can indicate direction from
where radiation came from Control badge can indicate if
exposed in transit
Only records exposure where it’s worn
Not effective if not worn Can be affected by heat
and humidity Sensitivity is decreased
above and below 50 keV Exposure cannot be
determined on day of exposure
Accuracy limited to + or - 20%
Pocket Dosimeter
The most sensitive personnel dosimeter Two types
Self-reading Non self-reading
Can only be read once Detects gamma or x-radiation
Advantages And Disadvantages Of The Pocket Dosimeter
Small, compact, easy to use
Reasonably accurate and sensitive
Provides immediate reading
Expensive Readings can be lost Must be read each day No permanent record Susceptible to false
readout if dropped or jarred
Thermoluminescent Dosimeters
Looks like a film badge Contains a lithium fluoride crystal Responds to radiation similarly to skin Measured by a TLD analyzer Crystal will luminescence if exposed to
radiation, then heated More accurate than a film badge
Advantages And Disadvantages Of The Thermoluminescent Dosimeter
Crystals contained in TLD interact with ionizing radiation as tissue does
Determines dose more accurately
The initial cost is greater than that of a film badge
Can only be read once Records exposure only
where worn
Radiation Survey Instruments
Area monitoring devices Detect and measure radiation Measures either quantity or rate Generally gas filled Major types of survey instruments
Ionization chamber - cutie pie Proportional counter Geiger-Müller detector Calibration instruments
Ionization Chamber (Cutie Pie)
Measures x or gamma radiation generally - can be equipped to measure beta
Measures intensity from 1mR/hr to several thousand R/hr
Most commonly used to measure patients receiving brachytherapy or diagnostic isotopes
Proportional Counter
Generally used in laboratories to measure beta or alpha radiation
Can discrimination between these particles Operator must hold the counter close to the
object being surveyed to obtain accurate reading
Geiger-Müller Detector
Generally used for nuclear medicine facilities Unit is sensitive enough to detect individual particles Can be used to locate a lost radioactive source Has an audible sound system Alerts to presence of radiation Meter readings are generally displayed in mR/hr