radiation protection stacy kopso, m.ed., rt (r)(m)

Radiation Protection

Stacy Kopso, M.Ed., RT (R)(M)

• Film Badges• Thermoluminescent Dosimeters• Optically Stimulated Luminescence Dosimeters• Pocket Dosimeters• Dosimetry reports• Radiation Survey Instruments• Dose limits• Principles of personnel exposure reduction• Construction shielding• Protective garments

MONITORING OF PERSONNEL

Monitoring of Personnel

• Late effect of radiation• Exposure to intermittent low doses of

radiation over a long period of time– Cancer and genetic effectsEffective dose limits have been implemented to

lessen the possibility of the occurrence of early and late effects of radiation

Monitoring of Personnel• Monitoring is mandatory when personnel are likely to receive 25% of the annual

effective dose-equivalent limit• Dosimetry- measurement of ionizing radiation doses to personnel. Record

external doses. Not a protection device!– Film badges– Thermoluminescent dosimeters (TLD)– Optically stimulated luminescence dosimeter (OSL)– Pocket dosimeters

• Normally monitored monthly• Records monthly, quarterly, yearly and lifetime exposure• Worn outside lead apron at collar level (different locations for specific badges)• Pregnant woman

– 2 badges• Collar outside apron• Waist under apron

Monitoring of Personnel

• Film Badges– Special radiation-dosimetry film (similar to dental)

contained in a light proof package– Film is enclosed in a plastic holder– Metal filters shield certain parts of the film that permit

estimates of dosage and radiation energy– Shallow and deep doses can be calculated according to the

amount of darkening of the film after processing– Worn outside apron at collar level– Worn monthly

Monitoring of Personnel

• Worn at collar level outside of lead apron • Control badge – kept in a radiation free area– Serves as a baseline when compared with the rest

of the film badges• Can only be worn during work hours• Kept away from sources of radiation and

excessive heat and high humidity

Film BadgeAdvantages Disadvantages

Simple to use Not reusable

Inexpensive Low limit of sensitivity (10mrem)

Readily processed by laboratories Accuracy limited to (+ or – )10-20%

Provide a permanent record Susceptible to heat, humidity and light leaks

Monitoring of Personnel

• Thermoluminescent Dosimeters– Contain lithium fluoride or calcium fluoride crystals– When exposed to ionizing radiation these crystals store

radiant energy when heated– As they are heated the crystals release energy as light– This is measured by a machine that documents the

radiation exposure based on how much light is emitted– There is a direct relationship between the intensity of light

emitted and the radiation dose received by the crystals– Commonly worn as finger rings by nuclear medicine

personnel (handle radioisotopes)

Thermoluminescent DosimeterAdvantages Disadvantages

Can be made very small No permanent record (no archive)

Durable Expensive

Low exposure limit (5mrem)

Accuracy +/- 5%

Less sensitive to heat

Can be worn for three months

Are reusable

TLD

Monitoring of Personnel

• Optically Stimulated Luminescence Dosimeter (OSL)– Contains filters composed of aluminum, tin and copper– Houses a thin strip of aluminum oxide– The strip is stimulated by using a laser light and becomes

luminescent in relation to the amount of radiation it has received

– Capable of measuring different energy ranges determined by the amount of luminescence detected in the areas underneath the filters

– These various ranges of energy correspond to deep, eye, and shallow doses

Optically Stimulated Luminescence Dosimeter

Advantages Disadvantages

Measurement range from 1 mrem to 1,000 mrem (most sensitive reader)

More expensive than film or TLD

Accuracy +/- 15%

Precision within +/- 1 mrem

Energy range 5keV to 40MeV

Complete re-analysis if necessary

Bimonthly readout offered

Tamper proof badge

Not affected by heat or humidity

Whole body, collar, waist (fetal), wrist

Measures exposure to x-rays, gamma rays and beta particles

Monitoring of Personnel

• Pocket Dosimeter– Sensitive– Instantaneous reading– Must be recalibrated daily– Only for exposures up to 200mR– Ionization chamber inside– Review the dosage by viewing a scale through an

eyepiece located on the end of the dosimeter

Pocket DosimeterAdvantages Disadvantages

Provides an immediate exposure reading No permanent record

Measures up to 200mR Not damage proof

Pocket Dosimeter

Monitoring of Personnel

• Dosimetry report– Measured in mrem– “M” minimal exposure (1mrem)– Must transfer the cumulative total exposures and

the remaining dose to new employer

• Radiation safety officer (RSO)– Determines if an employee has received an

overexposure based on the report, the employee is counseled by the RSO

– Medical physicist, health physicist, radiologist or any other qualified person

RADIATION SURVEY INSTRUMENTS

Radiation survey instruments

• Used to detect and measure radiation• Geiger-Muller detector– Detects alpha and beta radiation– Inert gas-filled tube that briefly conducts

electricity when a particle or photon of radiation temporarily makes the gas conductive

– Tube puts out a pulse which is displayed by a needle, lamp or audible clicks

Geiger-Muller Detector

Radiation survey instruments

• Gas ionization chamber (cutie pie)– Measures x-ray, gamma, alpha and beta– Used for measuring dose rates– Shielding effectiveness– Source containers– Radiation areas monitoring– Checking results following decontamination

procedures

Cutie Pie

DOSE LIMITING RECOMMENDATIONS

Dose-Limiting Recommendations

• ALARA– As low as reasonably– Time, Distance, Shield

• NRC ,State, Joint Commission (JC)– Enforces radiation protection guidelines– State license(varies per state)– Radiation machine registration (yearly)

• Effective Dose limit/Dose equivalent limit- the lowest dose of radiation that will maintain health with no ill effects

Dose-Limiting Recommendations

• Diagnostic radiology personnel– Annual effective dose limit

• ____rem• 5• ____ mSv• 50• _____ mrem• 5,000Negligible individual dose (NID)1mrem/year Minimal amount which does not need to be reported on the

dosimetry report

Dose-Limiting Recommendations

• Public– Annual effective dose limit for infrequent exposure

• ____rem• .5• ____mSv• 5• _____mrem• 500• Frequent exposure• .1 rem (1 mSv)

Dose-Limiting Recommendations Occupational Exposures (NCRP # 116) Dose Limits

Whole-body 5 rem (50mSv)

Lens of eye 15 rem (150mSv)

Skin/Extremities 50 rem (500 mSv)

Whole body cumulative (lifetime)30 yr old- 30rems

Age x 1 rem (age x 10mSv)

Fetus full gestation .5 rem (5mSv)

Fetus per month .05 rem (.5 mSv)

• Deep Dose Equivalent (DDE)– External whole body exposure

• Shallow Dose Equivalent (SDE)– External exposure of the skin or extremity

• Eye Dose Equivalent (EDE)– external exposure of the lens of the eye

mAs and Intensity

• Doubling the mAs, doubles the skin exposure, as long as other factors are held constant (factor of 2)

• If an original intensity was 200 mR and the mAs value is increased from 10 to 20 mAs, what is the new intensity?400 mR (increase by a factor of 2) Directly proportional

If an original intensity was 200 mR and the maS value is decreased from 100 mAs to 50 mAs, what is the new intensity?100 mR (decrease in ½)

kVp and Intensity

• Changing kVp affects radiation intensity by the square of the ratio

• If 50 kVp produces an intensity of 200mR, what is the new intensity at 100 kVp?– 400 mR (increase by 4x)

STRUCTURAL SHIELDING CONSTRUCTION

Structural Shielding Construction

• Primary protective barriers– Located perpendicular to the line of travel of the

primary x-ray beam– 1/16 inch of lead (PB)– Extends up to 7ft from the floor ( height of the

upright bucky)

Structural Shielding Construction

• Secondary Protective Barriers– Located parallel to the line of travel of the primary

x-ray beam– Cover areas exposed only to scatter and leakage

radiation– 1/32 inch lead (Pb)– ½ overlap on primary barrier– Plaster or concrete often serves as a secondary

barrier without adding lead

Structural Shielding Construction

Control booths• Secondary protective barrier• Window 1.5mm lead (Pb)• 7 feet high

Structural Shielding Construction

• X-ray tube– Lead lined metal covering– 1.5mm (1/16 inch) Pb– Reduces leakage radiation to not exceed

100mR/hr at 3 feet (1 meter)

Structural Shielding Construction

• Factors that determine protective barrier thickness include distance, time of occupancy, workload and use.

• Time of occupancy– Amount of time a hospital area is occupied by people– Controlled area

• Area occupied by radiation personnel (factor of 1)• Reduce the exposure rate to ˂100 mR/week

– Uncontrolled area• Area occupied by non-radiation personnel (public)• Reduce exposure to ˂10mR/week

– Hallways= factor of ¼– Stairways and elevators= factor of 1/16

Structural Shielding Construction

• Workload– Weekly average tube current and tube operating

time– Measured in milliampere-minutes/week

• Use factor– Percentage of time that the x-ray beam is

energized and directed toward a particular wall• Primary & secondary wall barriers/use factor of 1• Not a primary/ use factor of ¼

PROTECTIVE GARMENTS

Protective Garments

• Lead apron– High atomic number– Evaluated by half-value layers (HVLs)The lead thickness that will reduce the intensity of radiation to 50%– Worn during fluoro work, portables, holding a patient– Lead thickness of

• .25• .5 • 1mm Pb

– X-ray attenuation at 75 kVp for 1mm Pb is 99%– Maternity apron

• .5mm Pb + 1mm Pb around abdomen area

Lead Apron

Minimum lead equivalentNCRP #102

.25 mm Pb .5 mm Pb

Gloves Apron

Bucky slot cover Thyroid

Curtain Overhead barrier

.35 mm PbGlasses

EXAM CONSIDERATIONS

Exam Considerations

• Mobile exam– Proper communication– Clear room– Shield other patients and pt– Radiographer should position himself at right

angles to the patient– Go around a corner if possible– Exposure switch • 6 feet

Exam Considerations

• Fluoroscopic Exam– Wrap around apron– Lead gloves– Bucky slot cover– Lead drape

Exam Considerations

• Fluoroscopic exposure switch– Foot pedal or hand switch– Deadman (requires constant pressure)

• Cumulative timing device– Produces an audible signal when 5 minutes of fluoro time has

been used. Must be reset.• Intermittent/Pulsed fluoroscopy

– Reduces patient exposure• X-ray intensity

– ≤10 R/min– HLCF ≤5 R/min

Exam Considerations

Source to tabletop distance˃12inches (30cm) for mobile fluoro˃15 inches (38cm) for fixed fluoroTotal Filtration2.5mm AlImage intensifier2mm Pb

Inverse Square Law

• The intensity of radiation at a given distance from a point source is inversely proportional to the square of the distance of the object from the source

• When the distance from the x-ray target is doubled, the intensity is ¼ as much as the original exposure

• FormulaI1 = d2

2

I2 d12

Inverse Square Law

Inverse Square Law

• If a radiographer stands 2feet from an xray tube and receives an exposure of 1 mR/hr, what will the exposure be if the radiographer stands 4 feet from the xray tube?– ¼6 feet to 3 feet???4 mR