1. Protection1 Radiation Protection

2. Protection2 BENEFITS VS. ADVERSE EFFECTS

3. Protection3 EFFECTS n STOCHASTIC: n Random effects –non threshold, linear dose response relationship – e.g..: latent cancer, genetic effects n NON-STOCHASTIC threshold dose response relationship e.g..: cataracts sterility

4. Protection4 MAXIMUM PERMISSIBLE DOSE n maximum radiation dose that would not be expected to produce significant radiation effect (as far as we know) n Doses below the MPD should not result in either somatic or genetic response n MPDs specified for occupational exposure only n Known as dose limiting recommendations

5. Protection5 MAXIMUM PERMISSIBLE DOSE n Based on a linear, non-threshold dose response relationship –See “A” n All unnecessary exposure should be avoided

6. Protection6 WHOLE BODY OCCUPATIONAL EXPOSURE n 5 REM/year (5 rem = 5000 mrem) n (average: less than 100 mRem)

7. Protection7 WHOLE BODY OCCUPATIONAL EXPOSURE n Pregnant radiation workers: 0.5 rem/gestation period n Never a sufficient reason to terminate employment

8. Protection8 WHOLE BODY NON- OCCUPATIONAL EXPOSURE n 0.1 REM/year n used in the design of protective barriers (uncontrolled areas)

9. Protection9 PARTIAL BODY OCCUPATIONAL EXPOSURE n Lens of the eye: 15 REM/year n Skin and any extremity: 50 REM/year –application: fluoro and nuclear medicine –measured by special ring badges or bracelets

10. Protection10 CUMULATIVE MPD (old formula) n over the life of the radiation worker n determined by: 5x(n-18) –n = age in years –5 is because that is the whole body REM/year –18 points out that no one under 18 should be working with ionizing radiation If they do, their MPD is considered that of the general population

11. Protection11 CUMULATIVE MPD (NEW FORMULA) n 1 x age (of occupationally exposed individual)

12. Protection12 PERSONNEL MONITORING n Records of amount of exposure received n necessary when an individual might receive 10% MPD (radiology personnel only)

13. Protection13 FILM BADGES n Film sandwiched between metal filters in a plastic holder n density on processed film proportional to exposure received by badge n M = minimum exposure (not recordable) n must be worn right side up on the collar, outside lead apron (if worn) n Use 2 if pregnant: collar and waist n never leave in car or near any heat n wear and replace monthly

14. Protection14 TLD: Thermoluminescent Dosimeter n absorbs and stores energy in crystal lattice n when heated, excited electrons fall back in shell with emission of characteristic visible light n Lithium fluoride crystal n more sensitive and accurate than film badges n change out every three months

15. Protection15 PERSONNEL MONITORING REPORT n State and Federal government require a personnel monitoring program n record and maintain exposure records n monitoring programs may not exceed a calendar quarter n Cost: $6-8 month depending on volume

16. Protection16 Cardinal Principles of Radiation Exposure Cardinal Principles TimeDistanceShielding

17. Protection17 3 Cardinal Principles of Radiation Protection n TIME: as short as possible n DISTANCE: as far as possible (inverse square law) n SHIELDING: dense, high atomic number –often lead bonded to sheet rock –4” of masonry is equivalent to 1/16” of lead

18. Protection18 DESIGN OF PROTECTIVE BARRIERS n hire a radiation physicist n many vendors help n room design must be approved by the state prior to installation

19. Protection19 TERMS TO BE FAMILIAR WITH n Primary radiation: useful beam n Primary protective barrier: useful beam is aimed at n Rarely necessary to use greater than 3 lb/square foot n concrete, concrete block, brick or dirt may be used instead of lead

20. Protection20 TERMS TO BE FAMILIAR WITH Secondary radiation: 2 types: 1. scatter: when useful beam hits object 2. leakage: radiation emitted from tube housing assembly Secondary radiation barrier: –barriers designed to shield areas from secondary radiation –always less thick than primary barriers –lead rarely required

21. Protection21 SECONDARY RADIATION BARRIERS (CONT...) n Lead is rarely required: usually less than 1.2mm Pb (3/64”) n most are adequately protected with 4 thickness of 5/8” sheet rock n control booth is a secondary barrier n sheet rock and 1/2” plate glass window often all that is required

22. Protection22 FACTORS AFFECTING THE BARRIER THICKNESS n Distance from the source : inverse square law applies n Workload: – increase # exams/ week increase in barrier thickness –unit: mA-min../week

23. Protection23 FACTORS AFFECTING BARRIER THICKNESS (CONT.) n Use Factor: % of time in which the beam is aimed at a particular wall n kVp of operation: usually 100 kVp is assumed to be your maximum

24. Protection24 OCCUPANCY FACTOR n Controlled Area: occupied primarily by radiation workers n maximum exposure rate: <100 mR/week

25. Protection25 OCCUPANCY FACTOR n Uncontrolled Area: may be occupied by anyone n maximum exposure rate: <10 mR/week

26. Protection26 Radiation Protection Apparatus n Protective Tube Housing: must reduce leakage radiation to <100 mR/hr at 1 meter n Control Panel: must indicate exposure factors. –must indicate when beam is on –usually with a beep, bell, or chime, possibly a meter

27. Protection27 Radiation Protection Apparatus (Cont.) n SID indicator: must be accurate within 2% of indicated SID n Collimator: x-ray beam and collimator light must coincide to within 2% –must limit leakage radiation as well as the tube housing does : (<100 mR/hr at 1 meter)

28. Protection28 Radiation Protection Apparatus n Filtration: Total: 2.5mm Al equivalent 2.0mm added by manufacturer 0.5mm inherent (Pyrex of tube itself) n Beam Alignment: beam must line up with film n PBL: positive beam limitation automatic collimation: must be accurate within 2%

29. Protection29 Radiation Protection Apparatus Reproducibility: output intensity must be constant (within 5%) from one exposure to the next Linearity: output intensity should be constant for any mA/second combination for any given mAs (within 10%) Personnel Shield: must be impossible to expose a film unless you are behind a protective barrier