Radiation Protection Of Health Care Workers

1. Radiation Protection Of Health Care Workers • Kyle Thornton • RADL 70

2. 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

3. The Technologist’s Mantra Of Radiation Protection • Time • Distance • Shielding

4. 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

5. 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, radiationintensityincreases • The numerical change is squared

6. 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

7. Shielding • Structural barriers • Mobile shields • Lead apparel • Lead is the material preferred for shielding • High atomic number - 82 • Majority of scattered photons are absorbed

8. 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

9. 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

10. 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

11. Mobile Shields • Can be moved • Used in angiography, surgery

12. Structural ShieldingWhat Is It Used For? • Primary and secondary radiation • Controlled/Restricted areas • Uncontrolled/Unrestricted areas • Leakage radiation

13. Controlled/Restricted Area • An area with an active source of radiation • Limited access • Maximum weekly dose is 100mrem

14. Uncontrolled/Unrestricted Area • Areas accessible to general public • Radiation exposure cannot exceed 2mrem/week

15. Determining Barrier Thickness • Distance - D • Use - U • Workload - W • Occupancy - T • DUWT - rhymes with newt

16. Distance • Distance from source to barrier • Inverse square law applies

17. 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

18. Workload Factor • mA minutes or seconds per week • Total radiation output time during the week

19. 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

20. 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

21. 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

22. 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

23. 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?

24. 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

25. Personnel Monitoring • Generally accomplished through personnel dosimetry • Anyone receiving 10% or more of TEDE must be monitored

26. 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)

27. 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

28. 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% Advantages And Disadvantages Of The Film Badge

29. Pocket Dosimeter • The most sensitive personnel dosimeter • Two types • Self-reading • Non self-reading • Can only be read once • Detects gamma or x-radiation

30. 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 Advantages And Disadvantages Of The Pocket Dosimeter

31. 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

32. 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 Advantages And Disadvantages Of The Thermoluminescent Dosimeter

33. 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

34. 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

35. 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

36. 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