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